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Photograph of attic air conditioning air handler, condensate drips on floorAir Conditioning Cooling Coil or Evaporator Coil
Diagnosis & Repair FAQs

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Air conditioner & heat pump cooling coil /evaporator coil diagnosis & repair questions & answers:

These questions & answers help troubleshoot evaporator coil or cooling coil problems such as blockage, frost or ice formation, reduced air flow, leaks, cleaning, repair, or replacement procedures or other coil problems.

This article series discusses the diagnosis and repair of cooling coil or evaporator coil problems that occur in the air conditioning or heat pump air handler unit such as frost or icing, dirt, blockage, refrigerant leaks, or improper sizing. Our photo at page top shows the cooling coil in the attic air handler component of a central air conditioning system.



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Cooling Coil (Evaporator Coil) Diagnostic Questions & Answers

Schematic of an air conditioning cooling or evaporating coil (C) Carson Dunlop AssociatesThe cooling coil or evaporator coil is where building indoor air cooling actually takes place.

[Click to enlarge any image]

A cooling coil which is blocked by debris or ice and frost, or which is damaged can obstruct air flow and reduce air conditioning system output. The air conditioning system evaporator coil and problems include ice and frost build-up, dirt or debris blocking air flow through the coil, and damaged or leaky cooling coils.

These questions & answers about ice or dirt blockage of the cooling coil or other evaportor coil troubleshooting were posted originally at DIRTY COOLING COIL / EVAPORATOR COIL or at FROST BUILD-UP on AIR CONDITIONER COILS - you'll want to see the diagnosis and repair suggestions in those articles.

Question: if I close off the upstairs will that solve my air conditioner compressor and evaporator coil problems?

I've read through a ton of comments here, and I appreciate all of the answers you gave. It seems that there's only three causes for the evaporator coils icing issue. We moved into our house here in south Texas from Alaska about 9 months ago. It was a foreclosure, but things were in good shape, except for the compressor. The sellers agent replaced it free of charge and worked great up until 3 months ago. That's when the problems started.

First they could a leak in a joint right on the outside of the in-house unit, he refilled it with 5 out of the 12lbs that are supposed to go into the unit.

2 weeks later, another call to the tech cause of an icing issue. This time, with dye and an electronic sniffer, he said it was the coil itself, and it was COVERED in rust. $1000 later, labor only, thank you carrier warranty, i have a new evaporator coil.

This last week has been HOT here in south Texas. I've shut a lot of the rooms to save on cooling bills as I have since we moved in. Could me closing off the entire upstairs cause the system to keep dying like this? Thanks for the help to all of us! - Jeff Collins 8/7/11

Reply:

Jeff:

- leaks of refrigerant resulting in low refrigerant levels can indeed cause coil icing;
- improperly operating thermostatic expansion valve that does not meter refrigerant at proper rate can cause icing
- low air flow can cause icing - and of course several things can cause low air flow such as dirty filter or a blower fan problem

For sure, closing off part of a home is well within the normal things that a homeowner might do and in no way should it be capable of damaging the HVAC system. I suppose if someone could close enough supply registers as to greatly reduce airflow across the coil it could, however, contribute to an icing problem there.

Question: sweating on the A/C suction line

My suction line is sweating just before it enters the furnace and drips into the pan causing water buildup, therefore, shutting off my pump, and then shutting off the furnace unit. There is about 5" of pipe not insulated just before it enters the indoor unit. Will wrapping this prevent the dripping? - Sean 8/12/11

Reply:

Sean, most likely, insulating the suction line will stop condensation on its surface. You can use foam insulation tubes designed for that purpose.

A/C manufacturers recommend that the insulation be secured with plastic ties or a protective tape, and they emphasize that you should not crimp the insulation by the ties or tape since doing so will compromise its insulating value.

Question: central air coils keep forming ice, cleaning and filter changes didn't help; our system never reaches the set temperature on the thermostat

Our central air conditioning coils inside the house keep forming ice. We have had a repairman come out clean all the coils, inside and out. We have also changed filters. Could the possibility that my husband turns down the thermostat to 50 degrees when we turn it back on to cool the house, that it never gets to that temp, runs all the time, and refreezes? - Angi 8/28/11

Reply:

Angi even at a thermostat setting that keeps the air conditioner running constantly the cooling coil should not ice up - after all lots of people might use that setting - it's within the bounds of what people might do and the system design has to handle that setting.

More likely your system is low on refrigerant, or perhaps a refrigerant metering device is not working properly or you have low air flow across the coil due to a dirty blower fan, dirty filter, leaky ductwork, blocked airflow - the sorts of problems we discuss in the article above.

Since you've cleaned the coils and changed air filters, I'd look at
- refrigerant charge (if it's low there is a leak to find and fix as well as need to re-charge)
- blocked or leaky ductwork and reduced air flow across the coil, maybe also from a dirty blower fan

Question: diagnosing more reasons for ice build up on an air conditioner

I read this article and helped me to understand about what is happening on our air conditioning unit. This is the situation, a month ago i and my mom have purchased Hitachi Ras-25rc, at first i didn't know that the model we bought is i think included in a list of models that is for phase out. Recently i have noticed that water has starting to drip off our indoor unit. When i opened the suction grill to expose the evaporation coil and air filler i found out that there was an ice build up all over the evaporation coil. Do you think the reason of the build up is one among those written/stated above? but although there are reasons yet i cannot specify the problem that causing the building of ice on our evaporation coil.

I have been searching the internet about the model Ras-25rc yet i still cannot find any information about it. Can someone who is knowledgeable about Hitachi products help me in understanding Ras-25rc? all i have here is manual and i don't know if it is inverter or if it can cause us high bill or anything that is necessary for me to know. Thank you.. - Prince Jose Miguel 4/19/12

Reply:

PJM: I'm not sure we can reliably diagnose your system from just the information you've provided. Above we list several causes of ice formation on a cooling coil, of which the two most basic are a low refrigerant charge (or defective refrigerant metering device) or blocked airflow due to dirt or a dirty filter.

You have identified the symptom- ice, but not the cause.

You can yourself make sure that the system is clean and has good airflow. A tech is needed to check or correct a refrigerant problem.

Before giving up on the unit it is certainly worth an inspection by a trained HVAC service technician. Keep us posted -what you learn will help other readers.

Question: if the outdoor coil has ice on it is this low refrigerant?

Outside coil has ice on it and Thermostat is set at 73 but shows 75 in house is this low refrigirant - Anon 5/1/12

Reply: is this a heat pump stuck in heat mode?

Anon, outside coil? That's the compressor/condenser unit. Indeed there is a problem but it may not be low refrigerant, it could be that or other problems. I would shut off the system to stop the risk of further damage and call a service tech.

If your system is a heat pump, then possibly the heat pump stuck in heating mode could also show this problem if the refrigerant level were low or if any of the other causes of coil icing were present. That's because in heating mode at a heat pump, the roles of the outdoor coil and indoor coil are reversed: in heat mode the indoor coil is used to put heat into indoor air and the outdoor coil is used to obtain heat from outdoor air by chilling itself.

Question: HVAC unit not working; tech added refrigerant

(July 11, 2012) Sweaty Jane in GA said:

After one year, our HVAC multi-zone unit (Bryant) is not running at all. Last year our tech had to put in more freon and then in December 2011, he had to add more, because the heat was not working. It worked fine for 3 months, then out again in April. Now, he says we have a freon leak, and need new evaporator coils, after a supposed spring tune-up and more freon. Will the new coils fix the leaking freon or could it be elsewhere?

Reply: regular addition of refrigerant is poor practice - find and fix the leak

Sweaty Jane:

Indeed the freon leak needs to be repaired - otherwise your system is both contaminating the environment and creating a regular delivery route for the A/C guy. I can't say if the leak is in the coils or elsewhere - so before replacing the coils, ask to be shown where the leaks are occurring.

Question: do air filters restrict airflow at the cooling coi8?

(Aug 7, 2012) Judy said:

Do the air filters for the evaporator coils restrict the air flow around the coils on my manufactured home Nordyne unit as the handy man who came to repair the outside unit told me?

Reply:

Judy:

Do air filters block air from flowing over the evaporator coils?

Well maybe: if the air filters are dirty they restrict air flow. If the air filters are reasonably clean then the amount of air flow restriction is within the design limits of the equipment. Certainly DO NOT operate the system with no air filters installed. Doing so will allow dust and crud to accumulate inside the equipment, leading to more serious blocked air flow and an expensive cleaning bill.

Question: frost on the TEV

(Oct 18, 2012) Robert rtremmel@hawaii.rr.com said:

I have frost build up on the TEV and condenser inlet tubing of my geospring heat pump water heater. I had an error message of "clean filter" even though filter was clean followed by "heat pump failure" I noticed temp at inlet was 15f which is right at bottom of normal range. I think this temp goes below 15f triggering error message.

Would this be a sign of leak in the sealed system? How about faulty TEV? I am DIY'r with no HVAC experience but time on my hands. How can I test TEV or if a leak in system? The frost does not extend into the condenser coils itself, just on the inlet tubing and TEV.

Reply:

A dirty filter can slow air flow at and thus frost up the coil;

But frosting at the TEV may indicate low refrigerant or a dirt-clogged or failing TEV.

Question: AC unit freezing up - added freon, now it's freezing up again

(Oct 22, 2012) Tracy said:

One month ago we had an ac serviceman come out because our unit was freezing up. He cleaned out the system and put in more freon. Well, it is doing the same thing again. What needs done now? We can't afford to keep having service calls.

Reply:

Frosting can be caused by low refrigerant; but adding refrigerant is only a temporary fix since without finding the leak the refrigerant just leaks out again.

Question:

(Mar 4, 2013) sharon said:

H how much to repair a heat pump coil.

Question: Anon claims bad capacitor causes freeze-up if there is not enough freon

Mar 8, 2013) Anonymous said:

capacitors normally cause there freezing if there is enough freon.

Reply: Really?

Anon - the capacitor is an electrical device that starts an electric motor or keeps it running - that device has nothing to do with the freon charge.

Question: what are the signs of a freeze-up at the heat pump?

(Jan 31, 2014) Anonymous said:

what are the symptoms of a heat pump Freezing up.

Reply:

If by freeze-up you mean literally, that would not be likely to occur unless the unit heater or base heater failed or lost power. The unit would not work, and quite possibly the compressor motor would be destroyed if someone tried to run the unit. You might hear horrible clanging, or perhaps just a hum with no compressor operation.

About the prior remark, I'll be darned if I can understand the relationship someone suggested between the capacitor and freezing because of not enough freon. This looks odd to me. A capacitor is an electrical component that assists in starting an electric motor. It knows nothing about freon levels.

Question: condensate leaks out of the air handler or blows into the duct work

(Apr 14, 2014) MIKE said:

My issue has to do with condensation dripping off the coils onto the blower housing, then out any crack it can find. The issue has nothing to do with the coils freezing, or the condensation drains being plugged, a lot of the condensation is not draining off the coils fast enough to make it to the drains, it drips onto the blower housing

Reply:

This is a common problem in HVAC systems with high air movement rates and high indoor humidity. Usually the HVAC tech adjusts the system's operating rate to dehumidify the building adequately and, provided there is not an unusual indoor moisture source (wet crawl space, leaks) the problem is not chronic.

If your unit has an adjustable fan speed, run the system at a slower speed for longer intervals to solve this problem. If an HVAC system is over-sized (too much cooling capacity) the condensate blow-off problem is often worse because the system cools down the building too fast - before it has also removed enough moisture.

Question: why do we always connect the refrigerant inlet at the bottom of the coil?

(Apr 21, 2014) anil kumar said:

please give me the clarification abt cooling coil connections.Why we connect inlet all ways at bottom of the coil.

Reply: we don't

Anil it's not clear to me that the the inlet is always at the bottom of a cooling or evaporator coil. For example some refrigerator designs insert refrigerant at an evaporator coil top - allowing it to flow downwards through the coil as it changes from liquid to gas (absorbing heat and thus cooling the coil).

You'll see cooling coils in a variety of positions depending on the system design.

If you want to pass on to me where you read that "the coil inlet always connects at the coil bottom" I'll research the question further but on the face of it I think the premise of your question is incorrect.

Question: is it OK to re-use the drip pan overflow safety switch?

(June 16, 2014) Phillip said:

Can the auto shut down water detectors be safely reused after they have been soaked in water and have shut down the AC system one time, or do they have to be replaced once they've done their job?

Reply: Maybe

Phillip

That's a good question. The switch is expected to shut down the system before it has itself been flooded. If that's what happens the switch does not need to be replaced. Testing it would be easy - just set the switch in a pan of water or pour some water into the drip tray.

But if a switch was actually flooded and if its design and wiring connections were not intended for that submersion it would be unreliable in the future - risking internal corrosion for example - and I'd replace it. It's an inexpensive part.

If you give us a switch part number and brand we can research the specific details.

Some condensate switches such as the Condensate Cop are sealed units that operate magnetically - and should not be damaged by flooding.

See these articles on HVAC condensate trays, pans, and switches

inspectapedia.com/aircond/Air_Conditioner_Switches.php#CondPanSw

inspectapedia.com/aircond/Condensate_Drip_Tray_Defects.php#CondensateFloatSwitch

Question: worried about wet cooling coil after cleaning off mold

(June 30, 2014) Diane said:

Just had AC cleaned it was full of mold. The cooling coil is wet all the time. the mold will grow back. My health is suffering. Why does th coil stay wet?

Reply:

It's normal for the cooling coil to be wet because moisture from air passing over the coil condenses on the cool surfaces.

Question: leaky condensate pan "should be inspected"

(July 6, 2014) Rick said:

I am purchasing a home that has a 4 ton York AC system. My home inspector indicated that the condensate pan should be inspected since there is evidence of a leak (rust stain) on the side of the air handler. The seller had an AC tech certify the system but he did not inspect the pan.

I called a HVAC company and was told it typically takes an hour or two to open the unit and that they normally replace the coils if they are spending that much time. That sounds like BS. Is it difficult to do this inspection? How much does it cost to replace a condensate pan?

Can the pan be replaced without replacing the coils or does that depend on the unit?

Reply: goofy inspection report - the inspector was afraid to call for "repair" but that's what's needed

Rick

In my OPINION telling you to have an obvious defect "inspected" is a CYA move - if the condensate pan is leaking it needs repair or replacement, and a check of what got wet and what damage may have ensued is needed too.

"Certification" such as you describe is of no value.

The ability to replace the condensate pan without having to cut and repair refrigerant piping and other components depends on where and how the unit was installed. In some cases, yes the replacement is trivial, in others not at all. Sorry I can't see your system so can't say which.

But certainly replacing a condensate pan alone with no other system wear or damage is no reason to replace a cooling coil unless the coil is itself corroded or damaged.

Question: lost cooling at Carrier 38TRA024311 and inside I have a Air Handler Model FF1B - cleaning the coil helped

7/12/14 Peter said:

I have a 14 year old unit for my apartment. Outside I have a Carrier 38TRA024311 and inside I have a Air Handler Model FF1B. I noticed the apartment was not cooling. When I looked into the Air Handler the evaporator coil was completed frosted. I also noticed the blower motor not working. I shut off power over night.

I thought at first that the coil was frosting over because there was no air moving. But I was able to get the blower going by manually spinning the squirrel cage; I will replace the capacitor?

In any event - the blower running did NOT fix the frost build up. I tested it this morning and in just a few minutes the copper tubing was totally white and soon followed by the complete frosting of the evap coils. I shut it down - I know otherwise I can damage the outdoor compressor.

The coils don't look that dirty - obviously I will clean - but what do you think? I read low refrigerant can cause this. The evap unit looks surprisingly good but I know there are expansion valves etc that I can't see. Hot here in Florida! Thanks.

DanJoe - part of the reason I am even tackling this is because the a/c on my old Subaru (also 14 - don't like to throwaway things) stopped working and the dealer wanted $920 to replace what he said was a bad compressor. But I could see the compressor was spinning. Anyway. I bought some gauges and a Robinaire vacuum pump and a new expansion valve.

Replaced the expansion valve, vacuumed system and reloaded with R134 and now my Subaru a/c is now working fine. In my reading, they said that the expansion valve frequently caused ice build up. The valve was a pain to change behind dash.

My guess is that it may have been the valve because after I vacuumed the lines and turned the pump off - it held a vacuum - no leaks - so maybe it was the refrigerant level? Anyway I mention that because I wonder if it is possible for a layman like myself to even change the expansion valve on my air handler system?

The more I look at my coils - I realize I do need to clean them. Any products that you suggest? I plan on ordering (Carrier Products P291-0503 RUN CAPAC 5 MFD 370V OVAL) capacitor from partsmart.us - only $4. Thanks in advance for your patience.

Peter said:

DanJoe - I went out any bought some foaming cleaner for my evaporator coils. They are dirtier than I first thought. First pass - I still get frosting on coils and piping but not as much. Running a/c now to try and cool down the apartment. I ordered a 'Ge 5x370 Run Capacitor 5uf 370 Vac' capacitor from Amazon and will replace this week.

(Right now I am manually starting blower cage.) I am beginning to wonder if my freon is low and that is the cause of the icing. I will call a tech in this week to check but I have two questions.

Question 1. I have a set of manifold gauges that I used to fix my 14 y.o. Subaru's a/c this spring. Can I use them on my balcony unit to see psi charge? - what are normal readings?

Question 2 - will the new capacitor improve my blower or simply eliminate my need to spin the squirrel cage. Thanks. Can't believe how great this site is!!!

Reply:

Peter, in addition to replacing a fan motor start capacitor it sounds as if there is a low refrigerant problem or a refrigerant metering device problem frosting the coil.

Cleaning the coil was a good diagnostic move.

Peter

Do not hook up the gauges as you describe. Without also using a gas canister you may contaminate the system or lose more refrigerant. And pressure readings alone don't fully diagnose the trouble.

About a DIY expansion valve replacement, if cutting and soldering refrigerant lines is required there is risk of contaminating the system.

Reader follow-up:

Thanks for the reply. Dan Joe - first of all this is such an awesome site! The frosting was because my coils were dirty. Two cans of 'a/c safe foaming cleaner' from Home depot did the trick for $12. I will now stay on top of maintenance. Any thoughts on the capacitor? Does it just help to start the blower motor? I will get it this week. Right now I have Fan Speed set to 'ON'.

Reply:

Peter,

Your description of a fan that will run if given a starting spin is a good diagnostic of a failed motor start capacitor. (Sometimes the motor itself is failing and ultimately needs replacement). I'd replace the capacitor or add one - see

CAPACITORS for HARD STARTING MOTORS

for details.

Question: ice forming on a Carrier central air system coil -whole new AC system needed?

(Sept 3, 2014) G Johnson said:

My AC guy serviced me for my 6 mos check up and showed me some ice (not frost) that formed on my 1999 central air Carrier system.

He thawed the ice and then said I had a leak and I need a new system. I have a German Shepherd dog who sheds like crazy and there was hair in the coils after one month with a new filter. However, the AC has or at least, appears, to have been running nicely. I asked him to test to make sure I had a leak.

He said I had a small leak that would get worse. I asked him to add free-on for now while I shopped around to compare purchase options.

He said he gave me 2 pounds of free-on. My Question: Does this sound like I need a new AC? I just want to make sure.

Reply:

GJ

IF the AC system is old and its cooling coil is corroded, the tech may figure that the total parts an labor to fix corroded leaky parts is close to that of a new system.

On the other hand, if the system is generally in good condition but has a single specific leak that can be repaired, that cost may be considerably less.

Low refrigerant (which means there is a leak) is a common cause of frost or ice formation on the cooling coil, though there can be other causes.

It's correct that a dog-hair-clogged evaporator coil might ice up due to reduced air flow.

Ask your AC tech why he figures you ought to replace the unit rather than find and fix the leak. After all, if the leak were in a section of refigerant tubing that ought not be so costly a repair.

Question: icing on the suction side

(Sept 20, 2014) Anonymous said:
icing the suction side of compressor for screwtype compressor what is the problem

Reply:

Look for a refrigerant leak or a malfunctioning thermostatic expansion valve or refrigerant metering device

Question:

(Apr 28, 2015) Shakil said:
I want to assemble an air conditioner.I have have the condenser and evaporator coils.Can anyone please help me in this project?I am confused about compressor.If need i can give you size and picture of my coils..please help me.

Question: AC blows cold air but won't reach set temperature - could it be the thermostat?

our a/c is blowing cold air but temperature will not reach to what i set on thermostat. thermostat reads 79, and even when i set it at 74 or 75, it never gets cooler than 78.

this was also on a day it was 105+ outside. a/c was just serviced 2 weeks ago and reported in perfect working order, but thermostat was recently replaced. i don't THINK something is wrong with the a/c system, but is it possible the thermostat could be malfunctioning and causing these problems? any thoughts? - Alex 7/11/12

Reply:

Alex,

The thermostat is basically an "on-off" switch. If it's calling for cooling and the room temp never reaches the set temp on the thermostat, the problem is not likely anything to do with the thermostat. Only if the thermostat fails to respond to room temp would I think otherwise.

Depending on the size and condition of your cooling system, its installation details, duct work, capacity, and similar factors, in a home with high heat gain in very hot weather, the system may be unable to reach the set temperature. Your hvac service tech would probably check to see if the system is producing cool air at a normal temperature and that the air flow is not blocked or reduced by a defect such as a dirty air filter or cooling coil or duct defect.

Question: old refrigerator, chopped ice off the freezer, punched a hole in the tube

Probably not the place for me - I'm sure to get a couple laughs here but what the hell.

I have a really nice old refrigerator (1945 G.E.) that was in the basement of our cafe for years.

One of the staffers thought she'd be helpful chipping the ice off the freezer coils and put a hole in the tube.

Enough said. I love this old fridge. Before getting rid of it completely, I was thinking of converting it to a keg fridge and using an old dehumidifier refrigeration system. It is possible to relocate the evaporator. into the cooling space and the condenser/compressor outside without opening the lines as the fridge's top is removable.

My question is this: If I use a fan to circulate air over the evaporator coil inside the fridge and a fan on the condenser located outside the fridge, what happens to the pressures?

Would this system cool the fridge and be reliable? Note that as a keg fridge, the space once cooled would not be frequently opened - hopefully preventing frost buildup etc. - Jason 7/14/12

Reply:

Jason first the refrigerant leak has to be repaired and the system properly charged. You might be able to salvage the system by soldering or expoxying the hole and having it recharged.

It is difficult to solder aluminum but possible using the proper temperature and aluminum solder; epoxy is easier to try; because the freezer compartment is on the low pressure side of the system such a repair may work.

You are right that a dehumidifier is basically a chiller, but you'll probably find that the dehumidifier's operating temperature range is not designed to drop temperatures down into the range you'd use for refrigeration purposes.

Question: Gurgling heard in the cooling coils; I see a fill valve on my compressor - can I use it to top up the system?

Actually I also just looked closer at the compressor and it has a fill valve on it. I removed the bolt valve-cap and under it is a torx screw. Can this just be used to top up the system? I suspect it's just low based on the fact the freezer coil gets marginally cool but not enough.

You can hear gurgling in the aluminum coils. The condenser gets only slightly warmer than room temperature. The compressor gets very hot after a 24 hour period, while the inside of the fridge reaches about 3 degrees Celsius with ambient of 23 Celsius.

The other day it was 35 degrees C and the temp inside the fridge got to plus 10. Not cold enough for beer. Could the capillary tube be clogged from the idiots who had the fridge before me tipping it on its side? Can it be vacuumed out and fully recharged again? The compressor is so quiet you have to almost touch it to feel it vibrating.

So now, use the dehumidifier parts as explained below or have this fridge serviced by someone with a vacuum pump? - Anon 7/15/12

Reply: take a look at the sight glass on the refrigerant liquid line - do you see bubbles?

Anon: indeed you've reminded me of a diagnostic clue that I have forgotten to include in our HVAC notes: looking at a sight glass on the refrigerant line, or listening as you did, bubbles can indeed be an indicator of low refrigerant charge.

We describe watching the sight glass while charging a refrigeration system at REFRIGERANT CHARGING PROCEDURE.

I'm a bit uncomfortable with the idea of just "topping off" low refrigerant in that the equipment should never be leaking; it's best to find and fix the leak, though I realize that under time and cost pressure some techs just deliver refrigerant and move on.

Charging a home air conditioner is not a step I recommend to homeowners or a handyman; special equipment, training, even knowing how to purge and then hook up the gauge and charging equipment, matching the right refrigerant, knowing the right charge amount are all stuff learned in HVAC school.

Question: can exposure of the outdoor compressor/condenser unit to sunlight cause indoor air handler coil frosting?

Our AC units sit on the west side of the house in the sun every day, all day in the Vegas heat. We've had the units replaced twice. We are now again having problems with the one unit's fans not spinning around. Could it be because something in the attic is icing up? - Rhonda 5/11/12

Reply:

Rhonda hot conditions increase the load on the outdoor compressor/condenser unit, as the fan and condensing coil have to work harder to condense hot high pressure refrigerant gas back to a liquid.

But I'm not sure how I can translate that into an indoor coil frosting problem. Some homeowners try cooling down a super hot outdoor compressor/condenser with spray from a garden hose (don't soak electrical components, simulate rain fall straight down) to see if that improves system performance.

If it does, and if other measures check out on the system, providing shade without blocking airflow can help.

Question: Water Chilled air conditioner for a marine vessel

I have repaired a water chilled air cond for a marine vessel, our men renew the entire piping for HP and LP circulation, after install all, the refrigerant only able to inserted up to 30psi, when running the system, it wont let any refrigerant to be inserted, and the piping and cooling coil start frozen and ice build up.

I don't know what is the cause of defects, anyone can give some advises? thank you. - Dave 5/18/12

Reply:

Dave it's possible that a capillary tube or thermal expansion valve (TEV) is clogged or frozen. Keep in mind that the procedures for charging on the high side of the system expect liquid refrigerant while charging on the low side of the system can only be safely done with refrigerant in a gas form. Details are at REFRIGERANT CHARGING PROCEDURE.

Question: Water leaks traced to ice traced to coil icing: A/C not cool enough and water dripping out of the furnace

(Aug 7, 2012) Sharon said:

my AC blows cold air, but the temperature in the evening time don't reach to what i set on thermostat which is 75. the temperature for several days has been over 103. And sometimes there is water dripping from the furnest. I have change the air filter. I'm not forsure what is going on.

(Oct 6, 2012) Lonewoodsranch said:

My daughter noticed that the ceiling above her bathroom had a water leak. I checked, and there is no plumbing up there, but I did find that the tubing (refrigerant line?) in my attic dips down slightly and where it has a large hole in the insulation covering it right where it dips, water keeps pouring out of it soaking and staining the ceiling under it.

I thought it was a roof leak until I crawled around up there this morning before it warmed up outside. It's now 80+ degrees outside, the AC kicked on and when I went up to the attic to check, I saw the water dripping/streaming out pretty good. I ran and got a big turkey roaster pan and put under it. Is this something I can fix myself?

Is this indicative of a system problem? Do I need a tech to come out to my house? Help please.

Reply:

Sharon, water dripping out of your furnace risks expensive damage - sounds as if condensate is not draining out of the system - check for a blocked condensate drain. Indeed your system may also have a frost-blocked coil. A symptom would be reduced volume of air coming out of the supply registers. Sounds as if you need a service call.

Question: can old heat pump leaky coil be fixed?

I have an old heat pump that got a leak on its coil, I was wondering if this leak can be fixed somehow. My email address is gulfport54lady@yahoo.com Thanks.

Reply:

Anon, it is sometimes possible to patch a leaky cooling coil but if it's old, corroded, fragile, it'll need replacement.

Question: no air flow at some of the HVAC ducts, good air flow at others?

I understand that low refrigerant and low air flow can cause freezing I get that. But I have Carrier split heat system where the air handler is in the attic standing upright.

On top of the air handler are three air supply "taps". Two on front and one in the back. The two taps on the front go to the back of the house.

The one tap in the back goes to the front with spiders taps of off that to registers. The back tap off the air handler has no air flow what so ever. None at the register it feed.

I went to the first spider leg of this tap and took the duct work off and turned on the unit. No air flow and no blockage. Why would my unit have two taps with air flow and one with none and ice up every time I turn it on? Also I had the unit charged last night, which didn't take much. By 6 am this morning the coil was frozen. Any thoughts would be appreciated. - Anon 5/16/12

Reply:

If the same air handler is feeding all of the duct systems and two have good air flow while the third does not, you want to look for a closed duct damper, missing or leaky duct connections, a crimped, constricted air duct, or an air duct where internal insulation has collapsed.

There is a blockage or a closed duct damper or something to find.

Question: air leaks out of the drip line and cables at my air conditioner, freezing coils half way up

I was in my crawlspace under the house and noticed a lot of air coming from where the drip line and other cables were coming from.

My coils have been freezing but only about halfway up. Could this be a leak from the blower to the duct? Could this be causing my coils to freeze? - Alan 6/23/12

Reply:

Alan, I'm unclear what that air leak is - perhaps a leak out of the blower compartment? Out of a supply duct? If so it ought to be sealed, but I don't think that'd be a cause of frost formation; Refrigerant lines should be insulated. Coil frosting is discussed in the article above.

Question: outside fan shuts off quickly

(Aug 24, 2012) Mary said:

outside fan shuts off after 20 seconds...any suggestions?

Reply:

Mary this doesn't sound like a cooling coil problem, rather a control problem or a failed compressor.

Question: confused conflicting advice from HVAC contractors on cooling system SNAFUs

(Sept 8, 2012) Laura said:

The original installer of the compressor and coil has been onsite multiple times to add and take away refrigerant. Also, I have brought in 2 outside technicians from 2 seperate companies.

The original installer intalled a coil with 3 ton unit during the winter into an existing system and made one modification to existing duct work (added a 6 in. vent). My square footage of what is being cooled is 1200 to 1500 not counting the attic which has no returns or vents.

The coil begins to freeze instantly.

All 3 have varied solutions to the problem.

1 (original installer) said to add AC in the upstairs (remodeled attic and the system should balance)

2nd tech says its either the coil is too small compared to the furnace or to AC the upstairs.

3rd thinks it is the TEV cause his electronic meter (after adding 1.5 lbs) said low something side.

Then he went onto say if it isn't the TEV I should have him come out in the spring for a normal cleaning and he will re check the amount of puron in the compressor and if it is low we have a leak if it is fine and we replace the TEV and it still freezes then we either need to replace the coil (make it larger relative to the furnace) or replace the ductwork in the house.

I am confused in how to move forward. I am tired of the feeling of throwing nuts and bolts at an issue. Please help :D

Reply:

I agree that it's confusing to get conflicting advice. Someone who keeps changing the refrigerant charge quantity makes me nervous that they don't really know what's wrong and may have trouble properly measuring refrigerant to get the rigyt system charge.

Someone who says the system is not properly designed could be giving good advice IF the problems you describe have been there from the first day of original installation. If not, that is if the problems you see with the HVAC system are more recent, then something else has changed.

A bad TEV can cause improper refrigerant metering and poor or erratic cooling performance and icing.

IF we're going to "shotgun" this problem by trying various repairs or changes, start with the least expensive ones.

Question: turn off the iced-up heat pump

(Aug 11, 2014) lynn said:
Should we turn off the heat pump while waiting for repairman.

Reply:

Turning it off Forman hour or so may melt the frost. Then you may get a bit of cooling before it frosts up again. Or just Leave it off - that's safest as depending on what's wrong you may be avoiding further damage.

Question:

(Sept 10, 2014) Anonymous said:
outside unit will not shut off

Reply:

(Oct 9, 2014) Anonymous said:

What do you mean by outside unit will not shut off: is it the condenser unit that is not operating or that won't stop? The fan, the compressor?

Question: replaced defrost board and thermostat

(Dec 18, 2014) Robert said:
I have replaced the defrost board and thermostat switch that goes on the coils and coils still freezing up in winter time. Jumpered out reversing valve it is working. Any information would be greatly appreciated. Thank you

Reply:

Robert a TEV valve not metering properly or low refrigerant can also cause frosting. See also REVERSING VALVE on HEAT PUMPS

Question: LG Freezer problem

(Jan 5, 2015) Anonymous said:

I have a LG two door (freezer on top) refrigerator. Ice build up on the evaporator (compressor keep running) not cooling

I removed ice from the evaporator and replaced the bi-metal(defrost thermostat) and the defrost timer. (heater gives the reading for conductivity ). But it cooled for couple of days and SAME PROBLEM!!
Can anyone help me to sort my refrigerator out.. thank you very much indeed.

Reply:

Anon

Your service tech may check for low refrigerant - if that's the problem don't just add refrigerant: find and fix the leak.

Question:

(May 8, 2015) Anonymous said:

looking fo r coil size with these numbers bvr24-36-cky18 65

(May 21, 2015) Anonymous said:
what causes evap coil to freeze up

Reply:

Anon: look for reduced air flow across the coil - perhaps from a dirty air filter, or low refrigerant charge.

Question: I've been told closing off some rooms in the house can cause coil icing

My wife insists on closing two of the five rooms upstairs off, and sealing the vents. I've been told this can cause the coils to freeze. Is that correct, and if so, will opening the doors and removing the vent covers thaw it out or will I need to do more? - BDM

Reply:

BDM:

I don't think that closing off two of five rooms would be enough A/C air blockage to cause coil freeze-up, though indeed if most of the air flow were blocked that coil icing problem would be likely.

Only if closing off rooms resulted in a reduction of return air to the HVAC air handler might that cause coil icing.

Try closing off the rooms as you wish - just shut the registers using the adjustable lever. You shouldn't need to "seal" the vents. A little leakage out of them won't make much difference in system operation.

Then if you notice a reduced air flow at your other room supply registers you'll want to check inside the air handler (turn off power first for safety) to see if the coil is icing.

If it is icing up and never did before, and assuming that nothing else (like a dirty air filter) is blocking air flow, leave the system off for an hour or so to let the ice melt and go back to opening the vents in question.

Question: frozen coils, no air flow, found low refrigerant, added refrigerant, coils frozen again

(I have a very old Rheem) Frozen Coils with no air flow Saturday and Tech found little over a 1 lb low on R-22. Sunday better air flow not cooling, tech found he overcharged and removed R-22. System ran normal for 3 days. Thursday coils froze and tech (new tech, same company) found low and added.. ran normal.

Friday morning awoke to find no air flow and coils frozen again. Turing off AC and the fan on has melted the ice and air flow is restored.

Both techs were hesitant to look for leak with dye- and suggested putting that money into a new unit.

I know the unit is old- but am I crazy to try to find the leak? Compressor is a little noisy- but it has been that way the 6 years we've lived here.. and doesn't seem like it would cause loss of refrigerant. To get this fixed over the Holiday weekend- and quickly- I went with a company I have never used- so I'd love a second opinion. - Scott 7/8/11

Reply:

Scott:

Quite so: too much OR too little refrigerant can cause icing in the system. If it were me I'd ask the techs to find and fix the refrigerant leak. A leak in refrigerant lines in a system that is otherwise working fine is no reason to replace the equipment itself. And surely finding and fixing a leak in tubing is cheaper than replacing the whole system.

An exception to that view is if inspection discovers that the evaporator coil is so badly corroded or so much of other systems are so badly corroded that leaks are likely to be everywhere and recurrent - in that case it's time for a more extensive replacement.

Question: owner does her own diagnostics on poor air conditioner performance

Been waiting all day for the HVAC repairman and it is 100* out, so thought I'd do some research of my own & be knowledgeable when he gets here. First noticed this morning, house was warmer so I checked the air vents on both 1st & 2nd floors of my house & there was GREATLY reduced airflow, almost nothing coming out.

But I heard the A/C unit running on the outside of the house ...sounded a little louder than normal. I went and checked it & the metal piping leaving the A/C had a lot of ice build-up very near where the piping leaves the AC unit (this piping is covered w/a foam insulter(I am guessing)) & it is the piping that runs from the AC to the entry on the side wall of my house.

The only thing we have done differently in the past few days is adjust the lever on the furnace unit inside the basement so more airflow goes upstairs to our bedrooms & less airflow downstairs

& we shut the main floor vents to help force more air to the warmer area upstairs. I did have the thermostat on 65* for several hours but that was on almost 2 days ago, but when we got the upstairs cooled down, I turned it back to 70-72*. Any help would be great. Oh, also, the outside unit/fan was running fine, but had to turn it off to thaw it out, and haven't turned it back on because I don't want it to freeze again before AC guy comes to take a look. THANK YOU! - Kristen 7/26/11

Reply:

You're doing some good diagnostics on coil frost or icing on your air conditioner, Kristen.

The basics to check before calling the HVAC repair technician is to assure that both air handler indoors and compressor/condenser outside are running, that the air filter is clean and in place, and that no one has adjusted a supply or return air duct damper nor damaged ductwork so as to block air that should be flowing across the evaporator coil.

Provided the air routing adjustments you made didn't simply cut off air flow inside the air handler I wouldn't expect that to have caused coil icing. Let us know what your tech says - it may help other readers.

Reader follow-up:

Thanks for your comments

The AC repairman came and ran a test on our AC and it needed Freon, so far so good & it's been running for 6 hours trying to get back to a decent temperature in the house. It was up to 82* & now back down to 75*. Hoping to get it back to 70*.

I went outside (now after dark) & checked the pipe with a flashlight. No ice, but pipe is VERY cold since it has been running so long. Is it okay for the the AC to run this long continuously since we are trying to get the house to cool down?? Or do I need to adjust the thermostat to 75* and give the AC a break from running.

I'm not sure if these things are built for this/or meant to run this long continuously. We have about 2200 sq ft (I think) above ground 2-story, & another 800 square feet of finished basement, but mainly trying to get the upstairs sleeping quarters cooled down. I would hate for the AC man to have to make another trip out since he is actually about an hour from our house. Any thoughts ..I'm afraid the pipe could freeze again since it was so cold to the touch (even though the Freon level is back to normal). Thanks again.

Adding comments to my earlier problem w/freezing pipe on outdoor home AC unit.

The pipe did freeze again, & we figured out why on our own. Since it is okay now, we believe it was a combination of the low freon in the beginning, and our furnace fan was pulling so much air to cool the house that the filter was actually almost stuck in the slot (like it was pulling a lot of suction), not to mention when needed to change our filter.

So our diagnose for the freezing pipe as of now is this: a combination of low Freon, dirty furnace filter that was making it work overtime & running to long w/out lowering the indoor temperature enough, & we also had closed all the main floor vents, so we opened a few back up to make sure air was coming in and out properly. Hope this helps someone. - Kristen 7/27/12

Reply:

Good going Kristen on diagnosing those cooling system problem sources. You need a service tech to fix a refrigerant leak and charge a system, but a dirty filter or collapsing air filter are tasks most homeowners can tackle.

When your home has been quite hot for days, it could take the air conditioning system quite a while, (hours not days) to get the temperature back down, as the thermal mass of the home affects the cooling load. For example drywall walls and ceilings that are warm have to be cooled off too. - DF

Question: if I close off the upstairs will that solve my air conditioner compressor and evaporator coil problems?

I've read through a ton of comments here, and I appreciate all of the answers you gave.

It seems that there's only three causes for the evaporator coils icing issue.

We moved into our house here in south Texas from Alaska about 9 months ago. It was a foreclosure, but things were in good shape, except for the compressor. The sellers agent replaced it free of charge and worked great up until 3 months ago. That's when the problems started.

First they could a leak in a joint right on the outside of the in-house unit, he refilled it with 5 out of the 12lbs that are supposed to go into the unit. 2 weeks later, another call to the tech cause of an icing issue. This time, with dye and an electronic sniffer, he said it was the coil itself, and it was COVERED in rust. $1000 later, labor only, thank you carrier warranty, i have a new evaporator coil.

This last week has been HOT here in south Texas. I've shut a lot of the rooms to save on cooling bills as I have since we moved in. Could me closing off the entire upstairs cause the system to keep dying like this? Thanks for the help to all of us! - Jeff Collins 8/7/11

Lee said:

AC heat pump unit is freezing up inside, I guess the coils, and the outside unit had ice on one pipe. the unit is about 10 years old and i think it has only been serviced once during that time. I am recently divorced and broke. Will the heater work this winter, I can do without ac till spring, or do I need to repair or replace it to have heat? - Lee 9/7/11

Reply:

Jeff:

- leaks of refrigerant resulting in low refrigerant levels can indeed cause coil icing;

- improperly operating thermostatic expansion valve that does not meter refrigerant at proper rate can cause icing

- low air flow can cause icing - and of course several things can cause low air flow such as dirty filter or a blower fan problem

For sure, closing off part of a home is well within the normal things that a homeowner might do and in no way should it be capable of damaging the HVAC system.

I suppose if someone could close enough supply registers as to greatly reduce airflow across the coil it could, however, contribute to an icing problem there.

Reply:

Lee you need a service tech to diagnose and correct the problem or just as you'll have no cooling now, you may have no heat in winter - which will, unfortunately, be costly itself.

You don't have to use the A/C in hot weather if you can tolerate the temperatures, though depending on where you live there could be mold risks if the indoor humidity is too high.

In winter, without your heat pump you'll be running on backup heat that is likely to cost more over the whole winter than the cost of repairing and using the heat pump.

Question: should I turn off a system with ice on the coil

(Oct 9, 2012) susan said:

ice build up on coil inside, should I be having this on or not using it

Reply:

Susan, I'd stop using the system, though in a cooling emergency, you may get temporary relief by turning the system off long enough for the coil ice to melt away. Still it needs repair.

Question: can running at cool nights cause the evaporator coil to ice up?

(May 31, 2014) Anonymous said:

The air handler in our attic is very large and recently has been freezing up. The AC Unit outside still runs but there is no air blowing out from our vents.

I have an AC Repairman who has years and years of experience and very reasonable. He is old school. He has been in our attic a lot lately and can't seem to figure it out when he is usually very good.

He says cool nights while running our AC could cause it to freeze up. It has frozen up several times over the last month but lately it has not been cool at night.

It is frozen as I type this and it is 85 degrees. My repairman said he looked at the air handler and cannot find anything wrong.

Should I just call another repairman and see if they can help and risk them being very expensive?

Any ideas on what to do? Thanks!

Reply:

I have tremendous respect for old timers in any HVAC or mechanicals field, but in this case I'm not sure your guy is correct. Cooler outdoor temperature does make the outdoor compressor/condenser have an easier time condensing high pressure refrigerant gas back to a liquid, but that would have nothing to do with coil icing. As long as temperatures in the house are calling for cooling and the AC system is thus running, cooler outdoor temps don't cause coil icing but rather, a refrigerant metering problem, leak, or lowered air flow are more likley to be the explanation.

Question: will dirty outdoor coils cause indoor coil icing

(June 4, 2014) Adam said:

Just curious if dirty coils outside on the unit would cause freezing internally? Thanks

Reply:

Adam, that sounds rather unlikely to me but not impossible.

Dirty outdoor condensing coils means the system has to work harder to produce liquid refigerant that then cycles through the metering valve at the cooling coil where its conversion back to a gas cools the evaporator or cooling coil.

If the available refrigerant were too low for any reason we might see coil icing.

But the common causes of cooling coil icing, discussed in more detail in this article series, are low refrigerant ( find and fix the leak before recharging), or reduced airflow (such as due to a dirty filter).

Question: once the cause is fixed, will frozen coils have damaged our AC System?

(June 11, 2014) Frozen Coils on brand new A/C Unit said:

Hi. I'm looking for an opinion. We just had two brand new brand new energy efficient A/C units put in at the end of February…

one on the first floor and one on the second. The first floor unit has been great, but the second floor unit has had trouble cooling since we got it. We’ve had the company out several times over the last 6 weeks. But our second floor hasn’t been cooling below 80 or 85 on hot days. The drip pan has been full of water and the safety switch shuts off when the water gets too deep.

They thought it was a pump issue

Finally a tech came out today, opened it up and found that the coils were frozen solid.

Not just a little ice, but 2-3 inches all around it. The tech thinks the installers left the unit’s manual inside up against the coil which would have totally blocked the air flow. I didn’t think to ask him why he believes that as you can’t see a thing through the ice (makes me believe they’ve had this issue before). In any case, the unit is open and thawing and he is due to come back later today to check on it.

However, I can’t help but wonder if this issue just reduced the life of our brand new unit. We have a warranty on it, but I have to look up the timing and the coverage.

I’m wondering if we have a unit that should last 10 years that now may crap out in 5. Not to mention what it’s done to our electricity bills these last couple months! Assuming the coils thaw, they’ve identified the issue properly, and all works well…should I be worried about the life of our unit now?

Reply:

Frozen,

Shut off the system. When the ice has melted, tf there is no coil obstruction and air blows across it at a normal rate, I suspect an improper refrigerant charge or a bad refrigerant metering device. Fixing these should not leave the system with a reduced life.

Question: ok to install a window air conditioner on its side to fit a narrow window opening?

(Aug 2, 2014) C. Scott said:
My window is only 12" wide. I thought about turning a window unit on its side to make it fit. Will that bother the unit? Affect condensate drainage?
Thanks.

Reply:

Scott, do not turn the AC on its side out of normal position. Rather, there are special narrow-window units, that's what you want.

...


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