Air Conditioning Troubleshooting & Diagnosis FAQs (list of frequently asked questions about air conditioners)

These questions & answers about fixing problems with air conditioners & heat pumps were posted originally on the air conditioning & heat pump home page.

Typical air conditioner concerns include compressor or blower assembly noises, failure of air conditioners to start or to keep running, inadequate cool air flow or air quantity, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely.

Also discussed are various electrical wiring, fusing, overcurrent, and thermostat or control defects on air conditioners.

Air Conditioning Systems & Equipment FAQs-2

These 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 GUIDE A/C or 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

 

I enclosed the compressor/condenser unit for my walk-in refrigerator - is that a problem?

I have a walk in refrigerator with a condenser compressor unit on the top, the ceiling was cut out to accommodate the condenser compressor placing it in the attic. The attic has now been renovated into living space and the heat from the condenser compressor on a warm day is unbearable.

So I enclosed the condenser compressor and ran a 10'x6" insulated duct from a shroud over the intake end of the condenser coil to the exterior to supply fresh air, I also ran a 16'x6" duct from the top of the enclosure to the exterior for exhausting the heat.

There is a fan behind the condenser coil that pulls air thru the condenser and blows on the compressor only for the length of time the refrigerator calls for cooling.

The shroud is not a tight fit over the front of the condenser about a 1" gap around the edges. I thank that I need a 6"duct booster fan on the intake duct to ensure adequate air flow and direction over the condenser coil to be controlled by a temperature sensor with contacts to control the booster fans on off time and to turn it on if residual heat builds up in the enclosure, also in the winter "Northern Wisconsin" to prevent it from getting to cold.

I don't want to reduce the efficiency by allowing the equipment enclosure to get to cold in winter or to hot in summer and create a damaging environment. I have not found information on the temperature range necessary to accomplish this.
I could use some advice on this situation,
Thank You On 2017-06-22 by Richard U

by (mod) Yes

I would check with the equipment manufacturer, but it seems likely to meet up the duct system with you describe is going to be undersized and we'll both reduce the effectiveness of the cooling system and shorten it's life

 

Carrier heat pump won't turn off

i have a carrier heat/ac unit on top of my house and the heater works fine, but it shuts off before the temperature is reached and I can hear the heat pump still working , but, no air is coming out or heat ..,

i usally pull the fuse on the unit and this fixes it temporarily, could it be the ignighter that or a photo scenser thats not cleaned off.
need a professnal opinion thank you steve in redding ca On 2017-04-28 by steve -

by (mod)

We're in heat mode, right? Are you running in backup heat? If so the compressor/condenser would probably stop.

When no air is delivered then the air handler or its controls are not working properly in that I'd not expect it to shut off before the thermostat set temperature is reached UNLESS the air handler's heat exchanger in backup mode is overheating.

 

A/C blower fan won't cut off

The fan on my AC unit won't cut off. The blower fan cuts on and off as you would expect with the thermostat, and it is cooling the house fine.

When I looked at the unit yesterday, the refrigerant line and the compressor were covered in ice. I shut everything off and let it melt off, but when I turned it back on today, the unit can still won't turn off. I can't find my information online on this particular problem, so I don't even know where to look On 2017-04-26 by Mike

by (mod)

@Mike, It sounds like the contactor has the contacts stuck closed. This is a common problem.

Check out the diagnostic and repair advice at FAN WONT STOP - LIMIT SWITCH - inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

it could be a bad fan control or even just shorted thermostat wires

 

 

e Trane single packaged 3 ton heat pump fan randomly cycles on and off

Any ideas why fan behaves this way. Have a Trane single packaged 3 ton heat pump that when the heat/cool switch set to off, the fan randomly cycles on and off.

If the switch is set to either heat or cool, the fan turns on and off with the cycles properly. Fan switch is set to Auto. On 2017-04-26 by Krjun

by (mod)

Kr

I would look for

- a loose wire at the thermostat or between thermostat and the air handler

- a failing fan control or switch

- a fan whose wiring, control relay, or start/run capacitor is failing

BUt the fact that the fan behaves badly only in OFF suggests the first of these: a loose or shorting wire, or perhaps a bad thermostat

 

OK to fence around my outdoor HVAC air unit?

I am replacing the fence around my outdoor HVAC air unit. It gets circulation from the top. I want to build the fence with a 12" clearance on just one side, more clearance on the other sides. Is this an acceptable installation for zip 34231, Sarasota County, Florida? On 2017-04-09 by BJ

by (mod) - need air space

BJ

I certainly doubt that the ONLY air circulation path at your compressor/condenser unit is "from the top" - air has to move IN, across the condensing coil and OUT.

Blocking either inlet or outlet will increase cooling costs and reduce the life of the compressor/condenser unit.

 

Diagnose corroded ends of tubing at A/C evaporator coil

I recently performed an inspection of a forced air furnace with heat pump. I noted corrosion around the ends of the evaporator coils, most notably near where the condensate is collected. Is there a common diagnosis for this condition? The unit is about 20 years old On 2017-03-10 by Jonathan Quigley -

On 2017-03-10 by (mod)

Interesting question, Jonathan, perhaps other readers will comment. Was the corrosion on fins or on the tubing? Was the tubing copper or aluminum?

Indeed a badly corroded coil may precipitate a complete AHU system replacement since replacing the coil alone on a 20 y.o system that is using an obsolete refrigerant may not make economic sense. It'd make sense to issue that near-end-of-life warning.

But light corrosion on the ends of refrigerant tubing on the sides of the cooling or evaporator coil is normal.

Jonathan: corrosion around the ends of the evaporator coils

It was on the copper tubing. There is a photo at this link

1 by (mod)

I took a look at (and downloaded to examine) your photo - I see what looks like light corrosion on copper refrigerant tubing and rust on the galvanized metal frame that holds the cooling coil.

It would be no surprise that there would be more corrosion lower on the coil - as in the photo - as more condensate will tend to accumulate lower on any sloped coil;

These diagnostic questions occur to me, and others might be raised by other HVAC service techs

1. most important, and not easily seen, is there corrosion, damage, or blocking to the cooling fins in the cooling coil body: depending on the severity, including more severe than what I see in your photo, that may mean end of life of the cooling coil and on a 20 year old system, possible system replacement as I noted earlier. With a light and inspection mirror it may be possible to get a look at the coil condition through the small triangular openings at the ends of the A-coil frame.

2. if during system operation we can see ice or frost forming on the coil sufficient to block air flow then I suspect low refrigerant, and thus a refrigerant leak that needs attention; again depending on leak severity and where it is occurring, that could also precipitate a more costly air handler and possibly compressor/condenser unit replacement.

3. Stains on the cleaning instructions label on the condensate collection tray suggest that there may have been tray overflow in the past; A service tech would check that the condensate drain is not blocked and that condensate leaks have not damaged the heat exchanger of the furnace presumed to be below the cooling coil in the photo - as serious rust or damage to a heat exchanger may make the furnace unsafe.

The replacement question arises because while it makes sense to do inexpensive repairs to keep using equipment as long as feasible, at some point we don't want to start throwing much good money after bad.

(with your permission I'll find a place to post the image and this discussion, so you might use our CONTACT link to contact me by email).

 

Question: HVAC repair costs?

(Feb 1, 2015) Avery said:
You've got everything covered except the price? How much does it cost?

Reply:

Avery,

I'm not sure what "it" is in your question. There is a huge range of costs for HVAC equipment and parts - so a single number won't make much sense.

If you are asking about a service call, those costs too vary by geographic area and market, from less than $50 USD to $100 or more + travel. There is also quite a range of markups that service companies apply to products that are used for repair or replacement.

What we might do is check the purchase price of specific parts used in a repair, but then too we need to consider how the HVAC service company prices their service business.

Question: air handler trips circuit breaker

(July 23, 2011) Air Handler tripped breaker said:

The motor checks ok no ohn reading on each leg of 110v side of motor, capacitor has ohms of resistance no swelling. Either the mother board or the relay.

Reply:

With power off, check first for shorted electrical wiring, next for a seizing motor or a motor with a bad start capacitor.

Question: AC blower short cycling on-off betweeen heating and cooling

(July 29, 2011) Charles Gullette said:

I recently had a new 3 ton 13 seer unit installed. It included a new compressor, condenser, and cooling coils and digital non programable thermostat. The existing 3 ton blower and heater unit were reused.

After installation the blower unit starts, runs about 15 sec and then restarts. there is no effect on the compressor unit. My tech. says the blower is starting on the heater relay and then shifting to the cooling relay on the blower control board. He claims this is not a problem but that the board may need changed in the future. I did not have this problem prior to the new unit installation. Could it be the thermostat wiring or is my control board going bad??

Reply:

Charles, I wonder if the new thermostat was wired exactly the same as the old one? And I agree that the circuit board could otherwise be the problem. I also agree that it's curious to have to change a circuit board after other components were swapped out unless either there is a compatibility issue (sounds wrong) or an accidental short circuit, or some mechanical disturbance that just pushed a failing component over its edge.

Question: AC making revving up sounds

(Aug 27, 2011) AC making "revving up" sounds ev said:

When my AC (Trane) is running is sounds like someone is revving an engine every few minutes. The indoor part of the system is in the attic and when the "revving" noise happens the sound below, in the house, is like a "Blue Northern" strong wind.
Any thoughts? Thank you! NF

Reply:

AC making revving up sounds

Please see

NOISES, HVAC SYSTEM DIAGNOSIS

I'm not sure about revving up - perhaps a cycling of a motor trying to start? or a loose fan blade hitting something? AC making revving up sounds

Question: 0 PSI on compressor high side

Hi new goodman h/p getting 0 psi on high side? help (Jan 2, 2012) george

Reply:

sounds as if the compressor motor is not working at all and/or a refrigerant metering device such as a thermostatic expansion valve (TEV) is stuck shut.

Question: switching to cooling mode blew 24V transformer

(Mar 24, 2013) james said:

i put t-stat in cool 24 volt transformer blew what caused this

Reply:

James

Perhaps a short circuit in the thermostat wiring

Question: water leaking out of air conditioner

janie said:

my air condition is leaking water out of it

Reply:

Janie,

Look for a condensate drain clog or pan leak.

For diagnostic help see BLOWER LEAKS, RUST & MOLD

Question: Compressor overheats, frosting, expansion valve troubles

(July 11, 2014) Dave in Toronto said:

Singer incremental under window electric unit.
Compressor over heated and has seized. Tried Super Capacitor with no effect.

Replaced compressor. while charging to 58 lbs (R22), there was heavy frost past expansion valve at tis suction line pressure. No sweating of suction line. Compressor overheating. Changed filter/dryer installed a few years earlier. Retested. No change. Resting pressure was 250 psi. Changed expansion valve for new one. Much less frosting, but still evident at 58 lbs pressure after recharging. Now has new compressor, filter/dryer and expansion valve. No other components to change other than C coil. What's going on?

Reply:

Dave, contamination may be fouling the TEV causing it to open or close erratically.

 

Question: Whirlpool Room Air Conditioner model WS092LW circulates hot air

(Oct 7, 2014) Joe Rouse said:

I have a Whirlpool Room Air Conditioner model WS092LW. Even if Whirpool no longer sells this model, where can I get info on the unit? Mine is moaning and ciculating HOT air! Suspect it's in need of coolant, but open to insight on this.

Reply:

Joe, your AC unit may have indeed lost refrigerant. Don't just add more without also finding and fixing the leak.

Question: getting heat in cooling mode

when I turn on my ac instead of cooling the heat comes on. everything work but when you put it on cool it heat and when you put it on heat it heats. is it my thermostat inside or something in the heat pump outside? 12/4/2014 Anonymous

Reply:

Anon if you are sure your thermostat switches are correctly set then I suspect a wiring error or a control board failure.

Question: cooling tower won't re-start; AC unit stops cooling after a couple of hours.

(Aug 20, 2014) Anonymous said:
We have 32 condos in my building with a cooling tower outside , whenever the cooling tower shuts off due to electrical storms or service that requires tower to be shut down my Florida heat pumps shuts off and will not start again unless we do it manually . Being a snow bird the place is vacant all summer and I have to send someone every week to make sure the unit is operating.The unit is 3 yrs old and works well

(Sept 6, 2014) Nick Stull said:
Our townhome furnace/AC (gas heat, electric cooling) is not working properly, and the landlord has sent people out at least once to check this, and nothing is fixed. We turn it on, it kicks on and the outside fan and inside blower seem to be working properly. A couple of hours later, the unit will have cooled our place a total of a couple degrees (from 78 to 76 in one run), before it stops cooling. After that, the temperature in our place gets stuck, and the airflow in the downstairs vents slows to basically non-existent, and we have absolutely no airflow in the upstairs vents. Any advice on what I could tell them to check for? And while it is a complete waste of money, is there any harm in me keeping the A/C on so they actually experience the problem, or will this aid at all in diagnosing the issue?

(Sept 9, 2014) Anonymous said:
A/C is not cooling...Compressor is running...pressures are all reading good...inside coil is clean but not getting cold...low side Freon line is not getting cold or sweating...high side line is warm...any idea what the cause is..??

Reply:

Look for a refrigerant leak, low refrigerant, ice-clogged cooling coil

(Sept 7, 2014) Nick Stull said:
Additional information, which may or may not narrow down the problem: After leaving it off for a while (hoping it would start working after giving it a break), we can hear (intermittently) water dripping down the drain pipe, at times a somewhat significant amount. But even if it was ice clogging the cooling coil, that would only indicate another set of issues it could be, among which would be either low or leaking refrigerant, right?

Reply:

Nick

Your note further suggests ice-blocked cooling coil troubles.

Question: new AC costs more to run

(Sept 9, 2014) Anonymous said:
I have had a brand new 4 ton heat pump 15 seer unit installed. I had a 4 ton 12 seer 20 year old unit removed. My new unit is costing more per month than the old unit. had a new thermal expansion value installed ,did not solve problem . they want to put a solvent in value cuzz they think a rust inhibitor is causing value to not work proper. Am going on 4 months can't afford electric bill.Should I go with another unit or try the solvent

Reply:

Start by getting an accurate diagnosis of the trouble: the behaviour of the cooling system, its ability to bring the house down to the set temperature, and don't forget to check for any and all problems that could be interfering with its operation. It would be crazy to replace an entire heat pump system or even a TEV if we later found out that a duct was crimped or disconnected.

 

Compressor runs in winter mode but not in summer mode

Heat mode works fine.
In cooling mode, air is blowing but not cooling.
Can reset breaker even though it isn't tripped and will start cooling again.
Noticed more frequently as outside air temperatures got cooler.
Seems to happen daily or every couple days, but all I do is reset the breaker and it works again - (Nov 26, 2014) Michelle

AC cooling works fine. Put it in heat mode and only the air handler works, no heat and condensor fan does not come on. - (Dec 27, 2014) scott

Reply:

Sounds like a control board problem or thermostat not set correctly

Michelle

When the air handler blows warm air in cooling mode

1. check that the aux heaters are not stuck "on"

2. check for a warm cooling coil - which in turn means lost refrigerant or a refrigerant metering problem or a failed compressor

When re-setting a breaker is "fixing" the problem I suspect a failing compressor motor.

Scott

If the outside heat pump unit is not turning on there may be a failed control, relay, or even thermostat wire connection.

Question: lights dimmed and AC no longer works

for 2 days the lights in the house dimmed for longer then normal before compressor kicked in 3 day no cool air? (Sept 24, 2014) Anonymous

Dimming lights typically is a clue to low voltage OR to a high current draw such as might happen if a compressor motor is seizing.

ron said:
thanks danjoe . the unit is only 5 years. iam hopeing its not the compressor but something causing the low voltage. thanks again ron

Reply:

Ron

Thanks for the follow-up. If you monitor voltage right at the meter or panel that can confirm low voltage from the electrical company. Rule that out to start. You might get the motor running with a new start/run capacitor.

Ron said:
thanks for the info dan. the ac guy showed up yesterday took the cover off went directly to the run cap. put a new in checkd Freon 20 min. later handed me a bill for 172.50 had I known I could have done it myself. knowledge is power. and MONEY. still not sure they go out thanks again.

Question: nothing turns on inside when we turn on the AC

(Sept 26, 2014) Anonymous said:
thanks for the info dan. the ac guy showed up yesterday took the cover off went directly to the run cap. put a new in checkd Freon 20 min. later handed me a bill for 172.50 had I known I could have done it myself. knowledge is power. and MONEY. still not sure they go out thanks again.

Sept 29, 2014) Roger said:
We have a 'heat pump', the outside unit starts up when required, how ever, the inside blower does not always come on. It works ok sometimes, but not always. When working normal, the temp is great.

(Oct 9, 2014) Ronda said:
We have a heat pump/ air conditioner unit. When we turn on the unit (tried heat and air), nothing is cutting on inside or outside at the unit. We have a Honeywell RTH6350D programmable theromstat and changed the fan from auto or on and even that is not working. Any suggestions on what could be the problem?

Reply:

Ronda
I'd start by confirming that there is electrical power to the devices. Also check for an open blower door or a condensate overflow pan that is full.

Question: York electric AC heat pump not working - fan keeps going

(Dec 8, 2014) Sharon L said:
Hi, I have a 10+ year old York electric ac/ heat pump. My heat was on (but the "heat on" notation on my thermostat didn't read that it was on and the fan kept running for hours. Is this normal? I am just wondering why the fan kept running while the house was not being heated---or not according to my thermostat anyway.

Reply:

Sharon if the heating system fan runs indefinitely I suspect that at the thermostat or at a fan limit switch the fan was set to ON rather than AUTO, OR the system was unable to reach the thermostat set temperature - a problem that deserves a service call.

Question: condensate runs down side of our AC Heat Pump

(Dec 16, 2014) Andy said:
We have an ac/heat pump. Condensation is running down the side of the unit from about 3/4 way up, then running off the roof, so much so it leaves a lg puddle on the patio. When the unit runs and shuts off this stream is constant but slows to a drip if the unit has not run in a while.What could be the problem or is this normal. I don't recall this happening in prior yrs

Reply:

Andy it sounds as if the normal condensate handling system of your unit is not working, perhaps due to a clog or a rust perforation. It's not normal to see water running on the outside of the unit. Ask your HVAC service company to take a look. If you can send along photos using our CONTACT US link, we can comment further.

Question: control board problem in AC unit

(Jan 5, 2015) George Kubo said:
Heat Pump fan comes on when you turn on the thermostat for heat but goes off after a minute. There is 24 volts on contractor relay coming from the control board when the fan is on BUT there is not 24 volts coming out of the control board to the contractor relay when the fan turns off. Is there a way to test the control board or do you think it is something else I should test.
Thanks,George

Reply:

George

I agree that it sounds like a control board problem. For someone not an HVAC tech a reasonable start is a close visual inspection of the board for loose or burned components.

 

 

 

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Continue reading at DIAGNOSTIC GUIDE A/C or HEAT PUMP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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HVAC repair guides

• AIR CONDITIONING & HEAT PUMP SYSTEMS
• DIAGNOSTIC GUIDE A/C or HEAT PUMP
• DIAGNOSTIC DETAILS A/C or HEAT PUMP
• EDUCATION COURSES A/C / HEAT PUMP
• ERROR CODES, HVAC
• HOW AIR CONDITIONERS & HEAT PUMPS WORK
• PARTS - AIR CONDITIONING or HEAT PUMP
• AIR CONDITIONING & HEAT PUMP SYSTEMS

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