Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked.Air Conditioner & Heat Pump Diagnostic FAQs
Q&A help Fix Air Conditioners & Heat Pumps Set#2

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Air Conditioning & Heat Pump Q&A

Problems with air conditioners & heat pumps posted originally on the air conditioning & heat pump diagnostic home page.

Second set of A/C & heat pump questions & answers on air conditioning & heat pump systems.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Air Conditioning & Heat Pump Troubleshooting FAQs-1

Flex duct in a horrible routing of excess lengths (C) Daniel FriedmanThese questions & answers about diagnosing trouble with air conditioners and head pumps were originally posted at AIR CONDITIONING & HEAT PUMP SYSTEMS

A good place to look for diagnostic procedures is DIAGNOSTIC GUIDES A/C / HEAT PUMP.

Also see this series of A/C & Heat Pump Diagnostic FAQs sorted by major topic area are given at AIR CONDITIONING & HEAT PUMP SYSTEM FAQs LIST

On 2012-07-19 by (mod) - AC is off but cool air keeps coming out

I'm guessing either your fan is in manual ON mode or there is a problem with the blower fan relay or control circuit.

On 2012-07-19 though turned off my ac off cool air was still running

I turn my ac off but the cool air was still running .what can cause this problem

On 2012-07-18 by (mod) -

Terry the problem you describe is one I'd expect to turn over to a trained service tech - as I'm not sure myself what's happening. Often what's reported with high head pressure is a thermostatic expansion valve that is stuck shut or dirt clogged or frozen up.

On 2012-07-18 by (mod) -

Michael, Sometimes the homeowner and the service tech are not on the same page even if the tech is sharp and well meaning - s/he may not have been an English major. But from your description alone, it sounds like low refrigerant and a leak fast enough to take frequent charges - not a condition you can live with without finding and fixing the leak. I'd call the service company manager and review the history and politely ask for some experienced help.

On 2012-07-18 by Terry

I had to replce both condenser fan motors because the bearings where to tight to spin freely. What is happening now is that the unit is running for maybe 4 or 5 hours than both the first stage and the second stage compressers are tripping on high head pressure. What would you suggest to try.

On 2012-07-17 by Michael

1st visit by technician said freon leak and recharged it but didnt find leak. Worked 1/2 day. Charged for service call and Freon. 2nd visit replaced capicitor, and recharged freon, still couldnt find leak. Charged for service call and part. A/C worked fine for 1 week. Now there is ice on the outside like before, so I presume freon is still leaking. Should I call him back or get another technician? Also Where could the leak be, and is it costly if it is not in the tube?

On 2012-07-10 by (mod) -

Prakash, oversimplifying, but if the system runs and produces cooled air at a good flow rate but the house is hot, it is most likely your tech is quite correct and the system lacks capacity. Also when a house interior is heated to over 100 it takes time to cool down all that thermal mass, all the while fighting heat gain from outside.

On 2012-07-10 by prakash

Coolig system is not working

On 2012-07-10 by (mod) - condensation that forms on the cooling coils should be entirely trapped by the condensate drip pan

Lena, condensation that forms on the cooling coils should be entirely trapped by the condensate drip pan found there. And yes, a very cold drip tray in a hot moist environment might generate condensation on its sides and bottom where the condensate then drips out of the system. But HVAC equipment designers consider problems like that - I'd ask your HVAC service tech to take a more careful look at the system, as the problem for which you asked for help continues to occur.

Cleaning the coils and adding refrigerant ? I'm not sure how that would have fixed a condensate leak problem unless the tech thought that the cooling coil was forming so much ice that when it melted water leaked out of the system. And HVAC equipment does not normally consume refrigerant, so if you had to add refrigerant to your system, it'd be best to find and fix the leak rather than to just keep adding refrigerant.

On 2012-07-10 by Lena

I just had my A/C serviced yesterday (coils cleaned, gas & refrigerant added.) The reason for the call was because of a condensation problem. The pipe is clean and the pan is running the way it should. My problem is the condensation is coming from UNDER the A coils.

There are drip "catchers" on both sides and they are very cold, the temperature in the small room the unit is in is hot. Is it possible that the room is too warm and causing those to condensate? When the blower kicks on it blows the water all over inside and has been leaking down in the basement. I can't think of anything else that would cause it.

On 2012-07-09 by Matt

It was the capacitor. Swapped it out and blam, air conditioning.

On 2012-07-09 by tim

Man its hot. AC will come on for a short while. The fan inside the home work, filter clean, power on, the fan outside shuts down, neighbor mentioned hearing abnormal noises from the unit. The doors were open and shut for a party with 100 degree weather the other day, never had a problem in the past

. The slab that the AC sits on has moved a bit, not much but i did hose out a snake hiding underneath. I hate snakes, got him later in the day, could i have done some damage spraying underneath. Just tried it again, it sounds like it wants to start, ironic that it has a hissing sound coming from the outside unit. This sucks.
I would appreciate any suggestions.

On 2012-07-09 by Matt

York system, and it's pretty old, Came home from a week away and the house was 106 degrees. The blower inside was working, however; the fan outside was not. Reading here and following some suggestions, I was able to get the outside fan going and the thermostat is now reading 90.

Could it just be that we're having a massive heatwave and the house is going to take time to cool down is why I have non cool air coming out or should something to be more worried about? Neighbor said his shut off this week as well and his technician said it just overworked itself since the units are too small for the houses.

The vents are hot to the touch, but it seems to be wanting to cool. Could this be part of the problem?

On 2012-07-05 by (mod) -

Tina: regarding "air coming out of the vents is cool but not cold like usual" - if the home is very hot it is possible that it could take a while for air coming out of the supply vents to cool down - the system has to cool the whole duct system as well; It'd make sense to check for a dirty air filter or an ice-blocked cooling coil too -

but if the "cool air" supply never cools off, and if the air flow rate is not also reduced and those blockages I just named are not present, it's time for a service call. You might want to review the more detailed "lost A/C cooilng" diagnostic cases in the article above.

On 2012-07-05 by Anonymous

Alex, your question implies you suspect a dirt clog in the system on the high side - which is plausible it seems to me as well; but it sounds as if you need an experienced HVAC technician; "flushing the system" is not quite how it goes; I expect first the tech will check for a failing cap tube or frozen or dirt blocked TEV; it may indeed be necessary to replace a metering device or other control as well as to empty and recharge the system. If you suspect dirt or debris as a problem, or for that matter just as good practice, new filter/driers would be installed on the refrigerant lines after emptying the system and pulling a vacuum on it.

On 2012-07-05 by Anonymous

Alma you need to call your HVAC tech back and ask for a more complete diagnosis and repair; you are describing multiple problems - I'm not sure there is just one cause; for example wrong refrigerant charge or an ongoing leak can lead ultimately to inadequate or complete loss of cooling, but that doesn't explain why your system won't turn on in "AUTO" mode on the thermostat.

On 2012-07-05 by Anonymous

Anonymous: if the crawl area where HVAC ductwork is routed is freezing cold and the occupied space of the home is too warm when your A/C is running, I suspect a supply duct leak into the crawl area; Inspect the ductwork carefully for damage.

On 2012-07-05 by Tina

Got home today and the temp on the thermostat said 78 we have it set at 74 and it has now gone up to 79
the air coming out of the vents is cool but not cold like usual what could be the cause of this?

On 2012-07-05 by Alex Auld

I suspect a blockage in a 24000BTU split unit air conditioner. Compressor starts - low side pulls into a vacuum & high side pressure rises rapidly resulting in compressor overheating. How do 'n flush the system?

On 2012-07-04 by alma

also it will only run in the on position cant turn it to auto

On 2012-07-04 by alma Hinson

We had a new evaporator installed a few days ago, due to freon leaks and now when turned on the coils will get cold as long as the fan under it is not on , if we turn the fan on the coils get warm and it obviosly wont blow but warm air please help im at a lost here dont no where to turn.

On 2012-07-03 by Anonymous

I had a new central air unit installed last summer. If it's hot outside, my new system can't keep the house at the temperature set on the thermostat..74 degrees. To keep the temperature from exceeding 76 degrees I have to use all of my ceiling fans, a table fan, and the central air unit

. However, my crawlspace, where the duct work is located is freezing. In addition, during routine maintenance this Spring, the technician found the unit a full pound low on refrigerant.

I have had three service calls but each time I am told that the system is fine. I've lived in this house for 12 years and have never had this problem before. Any ideas?

On 2012-07-02 by (mod) - Check too for a dirty filter

Check too for a dirty filter, closed duct damper, crushed or crimped or disconnected duct work.

On 2012-07-02 by Jon

My outside and inside unit are working but I do not get right temp in entry level and no air flow on upper level. I observed I do not have too much pressure air circulation from basement either. System is new tech came he said it looks like duct installation problem.

On 2012-07-01 by vic

Air conditioning messed up for 3 days below is a detailed record of everything that’s happened:


Air on, working fine.
Fell asleep, when I woke up it felt muggy.
Checked thermostat- air was turned on.
Went outside checked unit, it was not blowing only making a buzzing noise.

Came in house, turned air off.
Took pitcher of cold water outside and poured over unit, checked to make sure that the fan could move freely.

Came back in turned on, still no air.
Went back outside, unit buzzing only.
Checked in basement, the breaker was thrown.
Flipped the breaker, air in basement cold.

Turned air on, checked outside unit seemed to be working normally blowing air.

Inside still hot and muggy, not really blowing through vents.

Checked basement, air cold, opened basement vent, blowing cold air.
Re-closed basement vent, upstairs still muggy and getting hotter.

FRIDAY – outdoor temp upper 80’s

Technician performs thorough cleaning of outside unit’s coils.
Air pressure in house air vents seem much improved.
Hours go by with unit running constantly, not much change in temp in the house.

SATURDAY MORNING – outdoor temp low 80’s

Air ran all night with no improvement on indoor temp.
Checked outside unit, line is completely iced over.
Turn unit off, ice thaws.
Technicians restore Freon levels to normal and adjusts belt on blower.
Air is cool and flowing in house.
Although thermostat is set @ 70 degrees, indoor temp never got below 80, close to the outdoor temp. Ran for 12hours straight.
Lines stayed free of ice.
Turned the unit off and went to bed.

SUNDAY MORNING outdoor temps high 70’s

Turned air on, heard very loud grinding banging noises coming from the outside unit that got progressively louder. Noise moved indoors and felt a rumbling under my feet where the furnace is.
Turned air off immediately, called technician.
Turned it on again, and was quiet and seemed to be running normally.
Removed filter in basement which did improve airflow somewhat.

Air has been running for 8 hours and still only not getting below 80 degrees.
current outdoor temp is around 80 degrees.

On 2012-06-30 by Jim

My inside unit responds to temperature setting and blower comes on blowing hot air. Outdoor unit was not running yesterday when I noticed house not cooling. I replaced the capacitor this morning and unit was working fine. It started warming up in the house again. Inside blower unit is still working but outside unit is not working again. Fan moves freely in either direction. Bad new capacitor?

On 2012-06-30 by (mod) -

Marnie, I don't know. I'd start tracking at the electrical panel - checking on power.

On 2012-06-30 by (mod) -

Lisa, diagnostics for the compressor fan are under FAN, COMPRESSOR/CONDENSER UNIT (search for this article title using the on-page search box)

On 2012-06-30 by (mod) - bad motor, bearing, voltage, start/run cap.

Steve, could be bad motor, bearing, voltage, start/run cap.

On 2012-06-30 by marnie

We have two air conditioning units that both stopped working yesterday. Why would they quit at the same time???? Both new or repaired within the last two years. Still waiting for a repair guy to call us back!!!

On 2012-06-30 by lisa said

I went outside this morning the motor was run but the fan was not. I need help bad, it will be 107 today

On 2012-06-30 by steve

i replace a condenser fan motor on a package unit it get so hot and keeping tripping thermal protective switch i did check the cap and wiring. what seem the problem ? could it be bad motor?

On 2012-06-30 by Laura

Turned on air for the first time today on my heat pump/air conditioner unit after some duct and thermostat work over the winter. Getting really good air flow but it's HOT air- not just weak cooling. House is getting hotter fast. Heat pump worked fine all winter with new thermostat. Could this be a mis-connected thermostat or more likely lost cooling capacity?

On 2012-06-29 7 by (mod) - if its 99degrees outside my unit should still be blowing cold air

Johnny when it is very hot outdoors your A/C system will surely run longer or even continuously; depending on its age and efficiency there could be a drop in cooling capacity but that would not be my first guess.

On 2012-06-29 by johnny r

if its 99degrees outside my unit should still be blowing cold air

On 2012-06-29 by (mod) - refrigerant is not a consumable substance


first, don't just "fill up refrigerant" - it's not a consumable. Ask that the leak be found and fixed.

Next, the answer depends on the setting of your thermostat.

On 2012-06-29 by Lillian

Hi, I have issues still. I had someone coming in to fill up refrigerant, and I turned on the air conditioning this morning at 9:00AM, when outside is around 24°C, inside was around 25°C. Now when it was 32°C outside, 2:00PM, inside is still 24°C. My house is single house. Is this normal? Or there is still problems with my AC? Thanks.

On 2012-06-28 by (mod) - warm suction line on 5 ton Trane unit

Steve I don't think we would have both a capillary tube used for metering refrigerant and a temp sensor - temp sensors operate a thermostatic expansion valve - a bad refrigerant metering device, either a cap tube that's clogged, or a TEV that is mis-adjusted, frozen, not properly sensing temperature, or internally clogged by debris all can stop metering refrigerant. The reversing valve is a separate part.

On 2012-06-28 by Anonymous

what are some other cause to do that ? could it be liquid line temp sensor bad that does that?

On 2012-06-28 by (mod) -

Steve you're making a reasonable diagnostic guess, I agree: if no refrigerant is returning to the compressor two bad things occur: excessive head pressures on the outlet side, and lack of lubrication on the low side -I would TURN OFF such a system pending a diagnosis by a tech, as those conditions can damage the compresosr.

Of course it could be something else but ...

On 2012-06-28 by steve

i have a 5 ton trane heat pump split system suction line is warm and it keep cutting my compressor off. Could it clog up in capililary tube or bad reversing valve ?

On 2012-06-28 by (mod) -

Gary, thanks for the interesting question. Answer is I don't know; it seems to me there is no single correct answer - temperatures in the two refrigerant lines (high and low pressure lines) vary considerably by refrigerant gas type, equipment type, and operating conditions. Traditionally the suction line is cold and the liquid line is hot. But in fact on some split systems even in pure cooling mode, that is not heat pumps, both lines can be cold.

On 2012-06-27 by Lillian

Thank you for your diagnosis. I had someone came in and turned out it is that refrigerant pressure too low, only 20+. He did check if there is leaking as well. He filled more and I will see the result this afternoon, since it will be 30 degree here.
Thanks a lot, it was very helpful.

On 2012-06-26 by Gary Scott

What should I expect the temperature differental between two copper pipes at the condenser

On 2012-06-26 by (mod) -

James, an A/C compressor that does not start until there is a wide temperature difference between the set temperature on the thermostat and the actual indoor temperature suggests either a problem with the thermostast (is it dirty or dusty) or with a control board in the equipment.

JP: if your home's A/C air flow is adequate in volume and temperature at some supply registers and is at zero at others, check for a supply register that is closed or a duct that has been closed off by a manual duct damper lever, or ductwork that has become blocked, crimped, disconnected, or has had an internal insulation collapse.

On 2012-06-26 by James

My air conditioner blows fine, but the compressor/condenser doesn't kick on until the temp outside hit at least 90, it just clicks. After it gets hot enough outside it will kick on and cool fine, but by that time the inside of the house is hot. It will run fine until it shuts off during the night, then it is the same thing the next day.

On 2012-06-25 by JP

My air conditioner only blows on 1 section of my mobile home. The rest of the house no air is coming through. Our air ducts look fine, and they were inspected in January. One hose under the house was full of water and it was drained, but still no air flow to the rest of the house. Any suggestions?

On 2012-06-21 by (mod) -

Lillian, if you have good airflow quantity but the temperature is never cool, AND if the outside compressor/condenser is running, the system may have a refrigerant leak.

On 2012-06-21 by (mod) -

Jim if the outside compressor/condenser never starts and provided it has electrical power, the tech will usually try swapping in a start / run capacitor - quite often that's the trouble and it's an easy cheap test to try. Other problems such as a bad relay or contactor can prevent starting, and of course more costly trouble such as a seized compressor.

On 2012-06-21 by Lillian

My room temperature only dropped 2°C after running a whole night. I started my AC last night around 5PM, and it was 34°C outside, 28.6°C inside.

Everything looks fine so far, except that it is still 26.5°C inside this morning around 7 AM. Overnight, outside temperature was around 24°C. I checked and there is strong air blow out of duct. What could be the problem?

On 2012-06-21 by Jim

Hello, My outdoor a/c unit will blow air through my duct work but the outside blower will not run. Plus my compressor is not working either. What you think.

On 2012-06-19 by (mod) -

Thanks Erin, glad to be of some help. Mom is indeed one of a kind.

On 2012-06-19 by Erin

THANK YOU for the common sense steps above - my breaker was off for no good reason! I didn't want to be like your mother, LOL!

On 2012-06-17 by (mod) - Condenser RPM

Condenser RPM question:

Thanks that's an interesting question and not a hypothesis I've come across. At least part of it makes no sense to me whatsoever, in particular, and reading your comment to refer to the outdoor condenser FAN unit not the compressor motor itself:

"But one tech guy told me that the outside condenser coils needed to get warm enough for efficient cooling to occur."

Think about what is happening in the outdoor compressor/condenser unit: the compressor condenses low pressure refrigerant gas into a high pressure high temperature refrigerant gas. That high pressure high temp gas enters the condensing coil. The outdoor fan blowing air across the coil transfers the heat of the high temp high pressure gas to outdoor air, AND in the process condenses the gas back to a liquid refrigerant that is then sent over to the indoor cooling coil.

Making the outdoor condensing coil hotter would not improve its performance, it would harm it, in general.

There could be something else, odd, going on, and it doesn't sound as if you've had a clear onsite diagnosis. Some fans can run at more than one speed or even variable - but usually at the indoor air handler not the outdoor unit. A bad motor, voltage, or control can cause the outdoor condensing fan to run at the wrong speed however.

It may be worth looking further for a problem with refrigerant metering equipment at the indoor air handler/cooling coil, or the system could have an improper quantity of refrigerant charge; I am SPECULATING that artificially slowing the delivery of liquid refrigerant back into the indoor equipment (slow outdoor condenser processing) might mask an indoor refriterant metering problem. Keep us posted, what you learn will certainly help others.

On 2012-06-17 by Condensor RPM's to high?

I have had this problem with my AC unit for some years now. techs have been out several times for free inspections, and nobody seems to see anything wrong other then try to sell me a new unit.

That costs $1000's. So here is the weird thing. When the condenser fan started to go out slowly but surely, for some reason the AC was working better then ever! Cooled on the hottest days. I know the condenser fan was running slower until the tech came to replace it.

But now that he replaced it, here we are again with warm air. Or shall I say cool air, but not really cold. Someone told me maybe the RPM rating of the condenser fan is too high, and over cooling the coils. I never heard of that. Or theoretically how is this possible?

But one tech guy told me that the outside condenser coils needed to get warm enough for efficient cooling to occur. Over cooling them won't allow the exchange to happen properly. Is this why we have been living with the cooling efficiency AC unit?

On 2012-06-16 by marty

compressor/heat pump won't run!

On 2012-06-14 by joyce miles

pipe freezing up

On 2012-06-09 by (mod) - Squirrels chewed up the thermostat wire

Tom, indeed as we learned from our local telephone company, there are some wire insulations that are very attractive to squirrels and other rodents. About the delay - maybe a bad connection or other damage that you haven't yet found? Intermittent electrical faults can be difficult to spot.

On 2012-06-09 by TomF

What the heck?

Squirrels chewed up the thermostat wire going to the condensing unit at a rental house we have. I repaired the damage and replaced the blown 3 amp fuse on the control panel at the furnace. The air still would not kick on.

I poked around a little more looking for other obvious causes but could find none. I gave up and called the company that installed the system 3 years ago. I scheduled an appointment for Monday (today is Saturday) and went on about my business. My tenant just called and said the air suddenly kicked on and everything seems to be fine. I was just curious as to what could have caused that delay. It was a couple of hours from the time I did the repair until it kicked on.

On 2012-06-09 by (mod) - if ice is forming where insulation

Bre: if ice is forming where insulation was lost on the refrigerant line replacing that material may be all that's needed. But abnormal icing on refrigerant lines is often a sign that the refrigerant charge is incorrect, and it can be a sign of a refrigerant leak.

On 2012-06-07 by Bre

We have a lot of ice on the copper pipe going into our 30 year old ac unit. (the pipe that is insulated). The filter is clean, and I'm not sure what to look for next.



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