A/C & heat pump cooling coil /evaporator coil problem diagnosis & repair Q&A:

These additional questions & answers help troubleshoot evaporator coil or cooling coil problems such as blockage, frost or ice formation, reduced air flow or other cooling coil issues.

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.

Cooling Coil (Evaporator Coil) Diagnostic Questions & Answers

The cooling coil or evaporator coil is where building indoor air cooling actually takes place.

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 also want to see the diagnosis and repair suggestions in those articles.

Question: Don't confuse a dirt-blocked coil from ice or frost formation on cooling coils

I cleaned the outside unit by removing the panel and the fan which was attached to some wires. I didn't disconnect or damage anything. I collected 1/4 a garbage bag with the dirt and debris found to the bottom. In attempting to clean the inside unit and fan, I noticed lots of ice on a grid like thingy and some tubes or lines.

The inside however looks to be pretty clean but I will wipe it down anyways. I purchased this house in 2006 and so far had to change the compositor battery looking thingy professionally.

2 years ago but still have freezing when it is about 100 degrees outside or more. What else could I do? How do I know if I need freon or refrigerant and where does it goes? Please help ...thank you! - Pamela 6/10/11

Reply:

Pamela it sounds as if you are describing frost and ice formation on the cooling coil (evaporator coil) inside the indoor air handler unit.

Icing coils are caused by low air flow (dirty cooling coil, dirty air filter or duct defects) or by a low refrigerant charge. Adding freon is something that needs a service call from a trained HVAC technician - it's not something a homeowner can or should try to do.

While ice or frost on on the coil could be caused by a dirty coil, the technician needs to defrost the system and inspect the coil as part of diagnosing and fixing the trouble.

If on defrost (just leave the system turned off for an hour or so) shows that the evaporator coil is actually clean, then the problem is elsewhere in the system and you'll want to see the diagnostic advice

at FROST BUILD-UP on AIR CONDITIONER COILS.

 

Thawing the frosted cooling coil helped air flow

On April 13th noticed unit had low air flow and wasn't cooling. Checked the unit it was iced up turned it off let thaw changed filters that helped air flow problem ,but wasn't cooling like it should.

April 18th had the AC people out he cleaned unit checked for leaks cleaned clog from drain pipe add a small amount of freon is cooling good but noticed some frost on the coils this morning when unit kicked on did he miss something or is this normal. On 2017-04-19 by Anonymous-

Repy

Adding refrigerant, if the refrigerant charge was low, could temporarily stop frost forming on and blocking the ccooling coil.

But unless the refrigerant leak is found and fixed the problem will return. - Daniel

 

What causes ice on my air conditioner?

What is problem 4 tan AC just star all compressor ice after 20 mine before same problem I cancel the hitpum now is same problem On 2016-09-19 by Anonymous

by (mod) -

Low refrigerant or a bad TEV are common causes - search InspectApedia.com for COOLING COIL ICING to see details.

 

Would low refrigerant cause weak air flow at vents?

We had a water main break in January of this year.

The water department replaced our furnace, but not our air conditioning unit (evaporator coil housing) using plumbing subcontractors. When we went to turn the unit on two weeks ago, we had very little air flow from the vents.

The same company came out, and stated that "we needed a charge" and quoted a price of $350. He did not check for leaks, just checked the temp of the compressor. I told him we couldn't afford that at this time (something already wasn't making sense to me).

He stated that we could run the AC at 70 for an hour at a time, then turn it off for 2-3 hours and repeat. I wasn't comfortable doing that, so I just kept the 'fan' on, and ran that only. Fast forward to yesterday. It got cooler out. So, I tried turning the fan off. It wouldn't.

I tried turning it off at the fuse box and it still didn't shut off. I had to use the switch on the unit itself to get the blower to turn off...also, despite the fact that the blower is running, no air is coming through the vents. I called the plumber again.

e informs me that our control board is fried. He said someone must have "accidentally" turned on the AC and caused the e-coil to freeze up and leak all over the board. I receive his statement of what needs to be done, and it says "replace refrigerant; attempt to find leak if possible".

So, I called other HVAC contractors, and the three I spoke to said it sounded like someone damaged the coil when they replaced the furnace.

When I told my husband this, he informed me that the installers did not remove the top part when they removed the damaged furnace.

Basically, it was hanging, and they slid the new unit under it.

Also, a friend told me that anytime work is done on an AC unit, it should be checked to make sure it's fully charged (it wasn't). Is that correct? I appreciate you taking the time to read this! On 2018-05-18 by Jen

by (mod) - refrigerant charge doesn't affect airflow unless low refrigerant leads to frost or ice blocked cooling coil

Jen

Adding refrigerant (a "charge") if that's what was done, would most-likely have absolutely nothing to do with a lack of air flow -

UNLESS the refrigerant level is low enough that abnormal frost formation on the cooling coil is blocking the coil and thus blocking airflow.

If an air conditioner lacks refrigerant the air handler or blower unit will still run and will still deliver air, but the air would not be cooled.

If an air conditioner does not deliver air flow, the problem is with the air handler blower fan, a blocked cooling coil, or with crimped, blocked ductwork (or even something as simple as a clogged air filter).

It is possible that a badly corroded cooling coil, IF the coil was flooded, could be blocked by corrosion. That would indeed obstruct air flow. If that's the case it will be visually obvious.

Your friend saying that the refrigerant level is always checked when any work is done on an AC unit is NOT correct.

Why does my A/C keep freezing up?

After having my thermostat set to 60 all summer, yesterday I noticed the temp was up to 67 and the ac was frozen. I let it thaw and changed the filters. I turned it back on and at this point the temp was 73. It took 7 hours to cool the house to 64. Woke up and it was at 67. Frozen again.

The evap coil in the handler was frozen along with at least the pipe coming from heat pump. I let it thaw. Checked the coils which were clean on the outside and appeared clean on inside also.

Cleaned the blower fan with a rag and also noticed the condensate pan was full and not draining so I cleaned the drain and added tablets. Since I've lived in this apartment there has been very little airflow through all registers. What could be the culprit? On 2016-08-15 by Frozen AC?

by (mod) -

Frozen

Please read our diagnosis and repair aviice

at FROST BUILD-UP on AIR CONDITIONER COILS - and

also REFRIGERANT LINE FROST 

that explains what's usually going on. Cleaning the coils is a nice step but if refrigerant is low, finding and fixing the leak and installing a proper charge is what's needed.

 

Question: Replacement A-Coil (cooling coil) was too small?

If our a-coil was replaced by one not large enough would that cause our cooling not to be good enough when the it is very hot outside? Ours was replaced because it was leaking and now when it is very hot outside it wont cool the house more than into the 80's. Year before that we had a new outside condenser unit put in. (July 18, 2011) David

Reply:

David: if the new A-coil in your indoor air handler is significantly smaller than the one that was taken out, it may be that it's not providing enough cooling surface for the volume and rate of air being blown across it.

Take a look inside the air handler to see if there seems to be a larger (than before) space through which air moving through the air handler is actually bypassing the cooling coil and ask your HVAC tech about that observation. Let us know.

Reader follow-up:

The a-coil is a little smaller but supposed to be ok for our 3 ton system. The tech said no leaks but added 2lbs of freon (10 months since last added). Said our compressor valves were bad because of noise he heard. Payne compressor only 3 years old. Replaced compressor but hasn't been hot enough to see if it made a difference.

Reply:

David, an HVAC tech that added two pounds of refrigerant after one year of system use and told you that there are no refrigerant leaks leaves me mystified. Unless your system was short-charged in the first place, having to add refrigerant always means that we've lost refrigerant from a leak.

Take a look at the article linked on this page at Continue reading where you will find an ARTICLE INDEX to RELATED ARTICLES that includes a live link for REFRIGERANT CHARGING PROCEDURE

You'll see that in a residential air conditioner or heat pump the exactly correct amount of refrigerant is important for effective and efficient system operation.

 

Question: What causes intermittent delivery of cool air followed by no cool air

Our central air runs when we turn it on, but sometimes it blows cool air and sometimes it doesn't. Sometimes the air pressure is strong and sometimes it not. Sometimes the air will blow for 30 min and sometimes 3 hours. On a good day it doesn't seem to cool the house past 78 degrees.

The last 2 days in the upper 90's the ac would run, but there was little to no air pressure coming out and if there was a little air pressure coming out, it was not cool air.

Our indoor house temperature read 85 degrees. Today it is blowing hard and the air is pretty cool, but seems to still take a while to cool the house down and doesn't get below 78 degrees (It is about 90 degrees out today outside). I think the air coming out should be cooler as I have been in other houses with central air that are cooler. We have had this problem the past 3 summers.

We had a guys take a look and he said it could be a small leak somewhere and he just recharged the system.

I don't want to call out the guy again if I don't have to. Could the problem be a leak still or something else because it works semi properly inconsistently. Any help would be greatly appreciated. Thanks. (July 23, 2011) Marc

Reply:

First I'd see if the evaporator coil is being blocked by frost.

IF so and if the your service tech finds that the refrigerant charge is correct, I'd look for a control problem or an automatic duct damper problem since you note that when the system runs it's cooling capacity is satisfactory

 

Question: air conditioner coils still freeze up after cleaning with water

My air conditioner coils and fins are still freezing or icing up after cleaning them with water ...could there be something else wrong that it still freeze or ice up? I have to turn on and off the A/C 's thermostat every 15 minutes or so just to melt the ice and for it to cool up again. anything else i can do to fix this problem? - Jack 10/20/11

Reply:

Jack,

if the A/C or heat pump cooling coil is clean and air is flowing across it but it's icing, then I suspect that there has been either a loss of refrigerant (low refrigerant can cause icing at low charge until there is simply too little refrigerant left in the system, then no icing and no cooling)

OR there is a problem with the refrigerant metering device such as a sticking thermostatic expansion valve.

Either of those diagnoses and repairs will need a service call from a trained HVAC tech. Keep us posted - what you learn will help other readers.

 

Question: HVAC fan on continuously to help defrost an iced-up cooling coil?

Will leaving the HVAC fan on continuously help defrost an iced-up cooling coil?

Reply:

Tony:
Yep, leaving the fan on all the time is using the fan to help "defrost" the icing coil. But you still don't want coil icing - it's wasting energy and interfering with the cooling system.

Your A/C guy is right that a faulty TEV (thermostatic expansion valve) COULD be the problem but also there could be other causes (dirty filter, blocked air flow, or low refrigerant level).

 

Question: can a clogged condensate drain cause the evaporator to freeze-up?

Can a clogged drain pan under the evaporator cause the evaporator to freeze up? (Feb 23, 2015) Bob Mann

Reply:

Bob I don't see a connection between a condensate drain pan clog and a frozen evaporator, except for a rather indirect one: if the cooling coil is very dirty that dirt can block air flow and lead to a coil frosting or icing problem. If it is really dirty maybe some of that crud has fallen into and clogged a condensate drain.

(Feb 27, 2015) Bob Mann said:
thank you, I did clean it out, the water was about an inch above the base of the evaporator? It hasn't frozen up since I cleaned it. The filter was clean, maybe just coincidence. There was good water flow, I'll see what happens. Thanks again

Reply:

If you get recurrent icing problems on the evaporator I'd take a look at FROST BUILD-UP on AIR CONDITIONER COILS

 

Question: cooling coils on HVACR equipment in a cement company environment

What should be the recommended fin material and fpi for condenser coils in cement company enviroment?

Reply:

Matthew,
to specify a cooling coil fin material you'd want to list the corrosive ingredients you expect to be in the air.

Caustic dust is one possibility but there may be others. With that information I'd call the HVAC manufacturer to ask their advice. I suspect you're looking at a lower heat transfer rate and using stainless steel, or going with a conventional coil and water-washing the outside unit.

 

Question: frost on the evaporator coil, slugged compressor motor

I had frost on evaporator coil and suction line. cleaned dirty coil and melted ice by turning furnace on. Turned A/C back on but only got 75F at nearest register. Did I ruin the compressor? Is there a protection device for compressor? - Greg Nelms 4/17/12

Reply:

Greg, you could be running out of refrigerant. Running the compressor briefly = may be ok, but don't keep running it since compressor motors rely on the presence of refrigerant for cooling and lubrication.

Reader follow-up:

Dan,The day the coil iced up was an unusually warm day in NJ. Wife turned A/C on in the afternoon, I did not get home till 9 PM and found the iced condition.

The evaporator coil was excessively dirty {even though I change the 90 day filter every 45 days}. Temperatures here are back to normal and have not tried the A/C since that day. Afraid I slugged the compressor. - Greg Nelms 5/1/12

Reply:

Greg,

Unfortunately if the compressor was slugged, you can't un-do it. You can have the system cleaned and inspected. If the compressor is damaged it'll be noisy, or won't work at all.

 

Question: added refrigerant, but four days later ice was back - back to the original issue

Two weeks a go, we placed a service call for additional freon as we thought that was why air wasn't reaching thermostat setting. Service guy suspected a possible freon leak, but added 3 gallons of freon. Four days later, we were back to original issue.

I checked lines running into outside unit (where fan is located) to see that there was significant ice build up. We've turned off A/C for now.

I looked for filter, but couldn't find where one would be. Based on above sounds like dirty filter, faulty TEV or refrigerant leak are all potential causes. Anything else I should think of before calling a different service guy? - Brian 7/8/12

Reply:

Brian, at AIR FILTERS for HVAC SYSTEMS (article links listed at the ARTICLE INDEX the bottom of this article ) you will find a description of various places to look for the air filter on an air conditioning system - or search InspectApedia for "find the air conditioner filter"

"back to the original issue" sure suggests the problem was not cured, or your refrigerant leak is a big one; I don't like adding refrigerant to a system without finding and fixing the leak - HVAC equipment does not normally consume refrigerant.

Sometimes a tech will just add refrigerant because it's cheap and quick rather than tracking down a hard to find leak. But 3 gallons is a huge addition - a big leak - that ought to be found and repaired.

 

Question: can a bad fan capacitor at the outside condenser unit cause cooling coil frosting at the indoor air handler?

A tech replaced the dual run capacator on the outside unit of my heat pump system. The fan would not spin and he needed help over the phone to get the unit running again. Could an improper installation of the dual run capacator cause frost and icing? Previous to his visit I never had a problem with frost or icing. - Mike 5/24/12

Reply:

Mike, maybe in some way I don't fully understand. The fan on the outdoor comprressor/condenser cools the outdoor half of the system and thus permits condensing high pressure high temperature refrigerant back to a liquid form.

One would think that if the refrigerant didn't condense back to a gas it would not be properly metered into the indoor cooling coil and I'd guess that the result would be reduced cooling, not more cooling.

Usually an iced coil results from

- slower air flow across the indoor coil because of a dirty air filter or fan unit or an indoor blower fan that is not working properly

- a problem with the refrigerant metering device (TEV)

- low but not zero refrigerant in the system

In the link at the ARTICLE INDEX the bottom of this article under COOLING COIL see the article FROST BUILD-UP on AIR CONDITIONER COILS where we list other causes of coil frosting such as a dirty air filter or lost air movement capacity due to dirt build-up on the air handler's blower fan blades.

Let us know what your tech finds - it will assist other readers

 

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: evaporator coil and suction line keep freezing up

I have a 2005 Duroguard A/C hooked up to an old GE gas furnace. The evaporator and suction line freeze up constantly. Tech checked high side pressure only, it was good. Furnace blower motor, capacitor and filter were replaced and the unit still freezes. The thermostat works normally. I am beginning to suspect a bad TEV or cap tube. Does that sound like the problem? - Chuck 7/8/11

Reply:

Chuck: indeed if the refrigerant charge is correct and airflow across the coil is good but icing is still occurring, I'd suspect a bad TEV.

(Thermostatic expansion valve). Some TEVs are adjustable. And a TEV can be clogged or blocked by dirt, debris, or ice.

 

Question: ice formation at the point of entry to the cooling coil

I have a 20 yr-old amana ac unit, that is freezing at the point of entry, the hose into the furnace, a small coil of ice. It had been serviced last year with an addition of freon and a good hose down to improve air flow.

This year another good hose down after it slowed down and couldn't keep up. Now it won't keep up again, set at 74 and seems stuck at 77, checked and that's when I saw the ice. Have a dehumidifier in the furnace room going.. any thoughts? - Martha 7/19/11

Reply:

Martha, ask your service tech to check for a refrigerant leak or loss and also for proper functioning of the thermostatic expansion valve.

 

Question: persistent ice formation on the cooling coil, letting it melt off doesn't fix anything

My small apartment AC does not sufficiently cool my place. The thermostat is set on 75 and the temp is around 83 (I live in a very hot, dry climate).

There is ice/frost on my coil and so I called a repairman who told me it's because I have set the temp too low and "it will never be 75 degrees in here" and told me to turn off the unit until the ice melts, and to change my filter, then he left.

I changed the filter and the day after it's iced over again and still not cooling down. Should I call him back and have him check for something more specific this time? - Daisy 7/25/11

Reply:

Daisy, if the coil is frost-covered that means that either the air flow across the coil is blocked or reduced (say a dirty air filter) or the refrigerant charge is low (leak) or the refrigerant metering device is not working properly.

The advice from the repairman was a gift to you in that it's good starting advice and was probably free.

But now that we don't think the airflow is blocked and you've changed the filter, you need a service call to diagnose and fix the icing problem. If the unit's fan is working properly and moving plenty of air then I suspect a refrigerant problem.

 

Question: frozen pipe outside my air conditioner unit - bad switch not lost freon?

Pipe frozen at outside unit and the inside unit would stop running but the outside unit would continue to run. I made an appointment for service. T

he tech came out and checked my freon level, he said it was fine and suggested that my problem may be the compressor. I told him that I was out of town all week and did not notice any problem before I left. He then told me that severe weather came through the area a few days prior and I should call my insurance agent to file a claim.

The insurance agent sent someone out to check it. This turned out to be another heating and air company.

This guy said that the freon levels were good but s switch needed to be replaced. He replaced it but three weeks later I have the same problem and have no idea what to look at myself to see what the problem could be. My air filter is new. Both units come on and off together.

No registers are closed. I checked for dirty coils outside then went into the attic, up there the coils had frost on them hours after I shut everything down. - Jason 7/30/11

I have the same problem as Jason, only it is intermittent (once every two weeks or so). Ha,ve had two contactors(?) replaced since last year. What can I tell repairman to test next? - Jackie 8/2/11

Reply:

Jason if your inside unit (air handler, cooling coil, blower fan) stops running, I'm not clear how a bad outdoor compressor would make the inside air handler unit stop.

A bad switch can be the culprit and sometimes even a replacement part can be bad, or the conditions that burned up the first switch could burn up the second one, indicating that more careful testing and diagnosis to find a root cause are needed.

Jackie, I would be careful not to be too directive to the repairman; but I would press for an explanation of why the same part keeps being replaced; it's natural to suspect that a different problem is damaging the part that's being swapped out.

...

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Continue reading at DIRTY COOLING COIL / EVAPORATOR COIL - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• COOLING COIL or EVAPORATOR COIL
  • COOLING / EVAPORATOR COIL REPAIR
  • DAMAGED COOLING COIL
  • DIRTY COOLING COIL / EVAPORATOR COIL
  • DIRTY HVAC COIL CLEANING PROCEDURES
  • FROST BUILD-UP on AIR CONDITIONER COILS
  • RETURN AIR, INCREASE
• FROST BUILD-UP on AIR CONDITIONER COILS
  • FROST / ICE IMPACT on A/C
  • HEAT PUMP OUTDOOR UNIT DEFROST CYCLE
  • REPAIRS for FROST / ICE on COIL
  • REFRIGERANT LINE FROST
• REFRIGERANT LEAK REPAIR
• WATER & ICE IN DUCT WORK
• WET CORRODED DUCT WORK

Suggested citation for this web page

COOLING COIL / EVAPORATOR COIL FAQs #2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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