A/C & Heat Pump Outside Compressor/Condenser Unit FAQs #2

Frost / ice, shuts down or short cycles, hard start, won't run, short cycles, won't stop running, fan wont' run, fan won't stop, refrigerant oil, refrigerant pressure

Refrigerant Pressure Problem FAQs

Diagnostic Starting Point:

• REFRIGERANT PRESSURE CONTROLS & SWITCHES
• REFRIGERANT PRESSURE READINGS & CHARTS
• THERMOSTATIC EXPANSION VALVE TEV INSTALL, DIAGNOSE, REPAIR

Question: can't get up to working refrigerant pressure level

The discharge line from my condenser is giving only 100 PSI, even after adding R-22 to the low side. Is my compressor defective? - Carlos 8/11/11

Reply:

Carlos, could be a bad compressor but it could also be a bad thermostatic expansion valve that is not closing.

See

• R22 REFRIGERANT PRESSURE / TEMPERATURE CHARTS
• THERMOSTATIC EXPANSION VALVE TEV INSTALL, DIAGNOSE, REPAIR

Question: TEV metering device for refrigerant needs to match the condenser size (and evaporator coil size)

The metering devise need to mach condenser if is 4 ton set a 4 ton metering devise even on a 5 ton evaporator. - Anon 7/11/12

Reply:

Agree, though some TEVs can be adjusted within an operating range for most equipment in residential applications

See

• GAUGE, REFRIGERATION PRESSURE TEST
• REFRIGERANT GASES & PIPING - home
• REFRIGERANT LEAK DETECTION
• REFRIGERANT LEAK REPAIR
• REFRIGERANT SIGHT GLASS

HVAC Compressor/Condenser Fan Won't Start or Won't Stop Running

Diagnostic Starting Point:

• CONDENSER FAN WON'T START
• CONDENSER FAN WON'T STOP
• FAN, COMPRESSOR / CONDENSER UNIT  - home

Question: A/C not cooling, condenser fan not running

Several days ago I noticed that even though my air handeler was running the AC was not cooling, I foudn that the condensor was not turning, I flipped the breaker (that apprered to be in the on position) and it worked for awhile.

15 minutes later I noticed that the condenser was not operating again so I flipped the breaker again it corrected the problem. I then went on the replace the breaker which seemed to correct the problem, the AC worked normally for several days.

Now I find the condenser is not working again and flipping the breaker fails the correct the problem. When the condenser was working it was providing good normal cool air.

The system is 2 years old. I assume I have an electrical problem in the condenser. What is likely to cause this problem and how can I test for it (I have a test meter) but I want to be careful because I know that a coil can retain a dangerous electrical charge even when all power is off and disconnected. - Rick 7/13/12

Reply:

typically we see if the fan spins, if it has power, and if the controls and fan contactor are bringing power to the fan when the condenser unit starts up.

Reader Followup

My problem turned out to be a bad contacter (damaged by ants) - Rick 7/13/12

 

AC condenser is buzzing and fan not running

AC condenser is buzzing and fan not running - On 2020-05-25 by Roland -

Reply by (mod) -

I would leave power to the unit off. I can't tell from just the comment whether we have a bad relay or failed compressor or control.

Question: compressor starts, fan doesn't start, I hear a hissing

My compressor turns on but the fan does not turn (I can turn the blades by hand) within 10 t0 15 seconds I get a long a loud hissssssssssssssssssssss.

I have some more info on my a/c when the a/c is turned on by dropping the temp in the house the compressor turns on but the fan does not turn, if you start to turn the fan by hand it starts spinning.

When I turn it off by picking up the temp it stops.

When I drop the temp again nothing goes on. If I wait a few minuites and try it again the compressor starts but the fan still has to be started by hand. Thanks for any help you can give. Thanks for you help - Henry

Reply:

Henry I suspect a bad fan start-run capacitor

But see the diagnostic suggestions at

• HISSING SOUNDS, HVAC from A/C or heat pump system

Question: A/C not cooling, condenser fan not running - ants damaged a contactor relay switch

Several days ago I noticed that even though my air handeler was rinning the AC was not cooling, I foudn that the condensor was not turning,

I flipped the breaker (that apprered to be in the on position) and it worked for awhile. 15 minutes later I noticed that the condenser was not operating again so I flipped the breaker again it corrected the problem.

I then went on the replace the breaker which seemed to correct the problem, the AC worked normally for several days. Now I find the condenser is not working again and flipping the breaker fails the correct the problem. When the condenser was working it was providing good normal cool air.

The system is 2 years old. I assume I have an electrical problem in the condenser.

What is likely to cause this problem and how can I test for it (I have a test meter) but I want to be careful because I know that a coil can retain a dangerous electrical charge even when all power is off and disconnected. - Rick

Reply:

typically we see if the fan spins, if it has power, and if the controls and fan contactor are bringing power to the fan when the condenser unit starts up.

Reader Followup

My problem turned out to be a bad contacter (damaged by ants) - Rick

Question: new AC unit, has trouble starting up / compressor fan won't start

My air conditioner is new. It's been hardly four month since I purchased it. most of the times it tries to start 2 to 3 time and then get started and some times unable to start

I dont have stablizer in my house for ac. when it runs it runs smooth and when it trips same case occur like starting can you please comment the possible casuse - Waquar Zaidi

Took the top off the unit. The fans spins by hand but wont turn on and run. Could it be the condenser? - (July 20, 2015) Lewis

Reply: If the compressor motor runs but the compressor/condenser fan won't run

see FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs and check for a bad fan start run capacitor or a bad fan relay.

Wagar I'm surprised to read that a new A/C system compressor is not starting, but I suppose it could be a bad start capacitor or another bad control such as the Thermostatic Expansion valve.

There are perhaps a few mistakes that could happen during installation that could destroy even a new A/C compressor such as dirt in the system or an improper refrigerant charge or a bad TEV that slugged the comprssor with liquid.

I'm unclear about the second and third sentences of your question.

Reader followup:

2nd and 3rd sentence I would like to elaborate: when compressor starts its working fine I mean it cools the room I use to run it on 26 degree centigrade and when thermostat trips and after 10 to 12 mints when compressor again tries to start same problem comes. and some time with out problem, compressor starts in first attempt.

is this a compressor problem what will happen if I continue to run my ac in this situation. thanks in advance

Reply:

AHA Wagar,

I can't pretend we can really diagnose by e-text Q&A, but if I understand more clearly, you are saying that the A/C compressor starts and runs OK the first time, but after the thermostat is satisfied and stops the cooling system compressor/condenser, when the temperature in the building rises and the TT calls for cooling a second time, the compressor is having trouble starting.

A simplistic view would be to treat it as a "hard starting compressor" and install a hard start capacitor kit. But since the compressor starts OK cold, it might be a different trouble.

If the compressor is trying to re-start against high head pressure that is more difficult than starting "cold" when the refrigerant pressures are the same on both high side and low side of the system.

So I'd look into what would cause head pressure to remain high after the compressor stops running. In many HVACR systems, as soon as the compressor stops running the pressures begin to equalize on the two sides of the system.

See COMPRESSOR / CONDENSER DIAGNOSTICS

• HVAC COMPRESSOR WON'T START

For more diagnostic help see the article REFRIGERANT PRESSURE READINGS & CHARTS

and REFRIGERANT PRESSURE CONTROLS & SWITCHES

Reader followup:

it even having same problem in first time start and now these days after its thermostat satisfies its not restarting after several attempts.

what I am concerned is: is it a compressor problem? or capacitor. or possibly some thing else when ac start it works fine I am as far as cooling is concerned there is no problem with cooling once it get success in starting. - Waqar

Reply:

Waqar why don't you try a hard-start capacitor kit

Reader followup:

Thanks Mod, will definitely try actually I am away from my home town will reach in 15 days. I would like to thanks you for your support you provided and will let you know the results.

 

Question: Is the problem with the fan motor or the compressor motor in my condenser unit?

I've a Lennox outside a/c unit. The fan/motor and compressor are part of the unit. The fan was not spinning and the A/c is not running.

I've isolated the problem down to the fan/motor or the compressor, but don't know how to check or find out which it is. Any idea on how to check if the fan/motor is 'bad' or the compressor is 'bad'? - Fan or ... 7/23/11

Reply:

Fan or compressor: you could also have a bad control board, or relay switch in the compressor/condenser unit.

If the fan is bad and the compressor is OK you'll hear the compressor turn on at the start of a cooling cycle, though a bad fan and system overheating could later cause some compressors to turn themselves back off. Similarly, if the compressor is bad your fan motor would still run.

So I'm suspecting a control or switch problem.

Should my compressor ever run without the condensing fan running

Should my compressor ever run without the condensing fan running?

I have a 2 ton Heil central air unit.

I have worked on automotive AC, Automotive unit work done always had the condenser fan come on at the same time or shortly before and stop at the same time or stay on shortly after the compressor. does not seem normal to me. - On 2018-05-29 by Steve

Reply by (mod) - no

Steve,

I agree with your AC experience. I

f the compressor runs and the condenser unit fan does not, nothing is cooling the high pressure high temperature refrigerant gas down to a liquid and the system won't work.

I'd look for a bad fan relay, motor, or run capacitor, or even a bad control board.

The heat pump compressor stops but the condenser fan keeps going: OK?

Compressor runs for 30 minutes and stops, but the condenser fan is still going.

The heat pump compressor won't keep running - condenser fan still going - 2018-05-21 by Mark

and

Hi - My condensing fan continuously runs even with the thermostat off . What could cause that to happen ? - On 2018-03-23 by george Perry

Reply by (mod) - that's normal

Mark

It's normal for a compressor to stop while the indoor air handler continues to run in SOME situations such as a cool down cycle at the end of a run cycle.

Depending on the cooling load, the compressor may cycle on and off while the fan keeps going.

But if the outdoor condenser unit fan keeps going for hours after the condenser has last run, then something's probably wrong with:

• the fan relay
• shorted wires
• a bad control board the control board in the unit.

Alternatively, if by your notes you mean that the compressor won't run enough to produce cool air, indeed you need repair.

In that case the cause is not something I can diagnose from a brief e-text. It's time to call an HVAC service technician.

Question: Is the problem with the fan motor or the compressor motor in my condenser unit?

I've a Lennox outside a/c unit. The fan/motor and compressor are part of the unit.

The fan was not spinning and the A/C is not running.

I've isolated the problem down to the fan/motor or the compressor, but don't know how to check or find out which it is.

Any idea on how to check if the fan/motor is 'bad' or the compressor is 'bad'? - Fanor

Reply:

Fan or compressor: you could also have a bad control board, or relay switch in the compressor/condenser unit. If the fan is bad and the compressor is OK you'll hear the compressor turn on at the start of a cooling cycle, though a bad fan and system overheating could later cause some compressors to turn themselves back off.

Similarly, if the compressor is bad your fan motor would still run.

So I'm suspecting a control or switch problem.

Compressor/Condenser Unit Won't Run

Diagnostic Starting Point:

• AIR CONDITIONER WON'T START
• A/C - HEAT PUMP CONTROLS & SWITCHES - Is it turned on?
• BURNED-OUT COMPRESSOR
• CONTACTOR RELAY DIAGNOSIS & REPAIR
• CONTROL CIRCUIT BOARD, A/C

Question: outside air conditioner compressor made a loud noise, then smoked, now it seems to be working

My compressor made a loud noice,then puff of smoke came out.I turned it off,when I turned it on again it worked and is heating.any known reason for this? - (Jan 4, 2015) linda cape said:

Reply:

Linda I dont know what happens but it doesn't sound good. If it was really smoke -as in something burning, I'd leave the unit off and ask for a service call.

Possibly it was not true smoke but a refrigerant leak which might, depending on leak rate and weather, might appear as white "smoke'. - Also a need for a service call.

it's also possible your system is running but on backup heat.

DO let us us know what your heating service tech finds as it will assist other readers. And do not avoid a service call since if there was a leak or burn-up the system may be unsafe.

 

Question: I filled up my air conditioner with gas but it's not working: now what?

So what is the solution of this problem as I have already filled gas recently. Thanks !! - Anon 9/16/11

Reply:

You need a service call from an experienced diagnostician. We don't have enough information about your case to specify a fix.

Or take a look at

• LOST COOLING CAPACITY

for more diagnostic guides

Question: My air handler works but the outside AC unit doesn't come on all the time - bad compressor?

my air handler works, but the outside ac unit does not come on all the time.

It's intermintent. My HVAC guy did pressures and said I have a bad comprresser (20 year old unit) and I'm better off getting a new ac unit. Sometimes it will come on and stay on. Other times it will not come on at all. - JPI 6/16/12

Reply:

JPI, I'm in no position to second guess the expert who was on the scene - s/he sees clues and performs test way beyond what we can do in a text Q&A. But here are some thoughts:

a failing compressor motor can become increasingly hard to start; the tech can install a hard-start capacitor to get the motor running again - for a time - and it might be worth a try: that's an inexpensive part and usually fairly straight-forward to install.

 

Question: Our new AC won't keep running

uhm my A/C compressor broke about two weeks ago, we got a new one but when the fan starts the compressor works for a while and then it shuts down, and its turning on and off and I dont know whats wrong - Help. 7/25/11

Reply:

Help: if your new A/c won't keep running after it has just been installed, surely you should call the installer and expect it to be repaired under warranty - it's just been two weeks.

Even if all of the new equipment is in good condition, an example of a problem that could occur during compressor replacement is that contamination, moisture, dirt in the refrigeration system (which is made worse if a compressor burns up) can interfere with proper system operation.

 

Question: My AC won't work if I set the temperature down below 25C

my a/c is working properly when it is adjusted at 25 degree temprature, but if it is lower than 25, the compressor is disconnected by the overload protection. what is the problem with my a/c. - Mohamed 8/5/11

Reply:

Mohamed an A/C compressor may cut off on thermal overload due to overheating from local conditions around the compressor/condenser unit (no shade, very hot weather), an older motor that is failing, a start capacitor problem, or even a refrigerant metering device problem.

If there's nothing obvious to you, I'd get a service tech to take a look. Keep us posted.

Condenser unit fan runs but the compressor won't start and the contactor is welded closed

Condenser fan works but compressor will not start and contactor contacts are stuck closed what are the steps to solve - On 2017-07-31 by Jim

Reply by (mod) -

Jim

Watch out for death by electrocution - if you're not trained to fool around inside the equipment it's rather dangerous.

That said, your tech would probably start by measuring the current draws - if it's abnormally high the motor may be seized.

Else she'll typically try the inexpensive shotgun repair approach: change out the start/run capacitor.

Heat Pump Won't Start on Hot Days and in Heat Mode Also won't keep running

This summer my A/C would not cool on very hot days.

In "heat mode" the unit starts, runs for 5-10 seconds and then stops - 2018-11-05 by Vickie -

On 2018-11-05 by (mod) - my heat pump short cycles on and off when in heating mode

Vickie

I am sorry that I can't offer a specific diagnosis but frankly we just have too little information to say anything useful beyond the compressor failure articles listed right at the end of the article above.

I would call an HVAC service technician for on-site diagnosis and repair help.

But before doing that, also take a look at our description of the common causes of air conditioner or heat pump "short-cycling" on and off, found at

SHORT CYCLING AC COMPRESSOR inspectapedia.com/aircond/Air_Conditioner_Short_Cycling.php

Hard-Starting or Failing Compressor: A/C Compressor Unit

Diagnostic Starting Point:

• BURNED-OUT COMPRESSOR
• CAPACITORS for HARD STARTING MOTORS
• COMPRESSOR / CONDENSER DIAGNOSTICS
• COMPRESSOR MOTOR REPLACEMENT
• HVAC COMPRESSOR WON'T START

How do I fix an Inverter AC Compressor that is hard-starting?

how can you fix an inverter AC compressor with a tight compressor issue ,if by hard starting HOW? - On 2021-01-06 by thomas

Reply by (mod) - fix an inverter AC compressor with a tight compressor issue

Thomas

a Service tech will typically try adding a hard start capacitor for the compressor motor. But beware that you are probably just squeezing a bit more life out of a failing motor.

Question: compressor just runs for a few seconds, then cuts off; short cycling A/C compressor problems

My condenser starts for a few seconds then cuts off cycle continues - Anon.

My compressor fun has started to short cycle, it run for 2-3 min then shuts off for one second then restarts runs again then stops etc. with no funny sounds or noises - Don

Reply:

It's not clear from your question where in the entire cooling system your unit's troubles begin, so I'd look at diagnostic tips that may explain your compressor/condenser short cycling are found

at LOST COOLING CAPACITY.

Certainly a compressor that is having trouble starting can be diagnosed

at HARD STARTING COMPRESSOR MOTORS, if you're sure the trouble is outside.

Question: My A/C Shuts Down if I set the temperature down below 25C

My a/c is working properly when it is adjusted at 25 degree temprature, but if it is lower than 25, the compressor is disconnected by the overload protection. What is the problem with my a/c. - Mohamed 8/5/11

Reply:

Mohamed an A/C compressor may cut off on thermal overload due to overheating from local conditions around the compressor/condenser unit (no shade, very hot weather), an older motor that is failing, a start capacitor problem, or even a refrigerant metering device problem.

If there's nothing obvious to you, I'd get a service tech to take a look at the current draw at the compressor motor - high amps is a sign of a failing motor.

Two helpful diagnosis and repair procedures are at

• CAPACITORS for HARD STARTING MOTORS
• HVAC COMPRESSOR WON'T START

Question: our A/C compressor tries to start but then shuts right back off

I turned my AC on and noticed it wasn't getting cooler inside, I went out to the condensing unit and the compressor tries to kick on but then shuts right back off.

Can not having enough refrigerant cause this? If not what's the deal? - Derek

Reply:

Derek, as another reader commented, your compressor/condenser may be having trouble starting. A start capacitor can sometimes fix this problem and give some added life to the unit.

Not having enough refrigerant would not itself prevent the compressor from starting, though there are some more technical connections one could draw (low refrigerant, sticking thermostatic expansion valve, high head pressure can mean hard starting - but that's not where I'd start).

At REFRIGERANT FLOODBACK, LIQUID SLUGGING we explain how liquid refrigerant entering a heat pump or air conditioner compressor motor can destroy it and we discuss the recommended time that the system should be LEFT OFF if was switched off while it was running

 

Trane XR12 heat pump won't start after changing thermostat wiring

Question- My wife and I decided to put a programmable thermostat on out Trane XR12 heat pump. We got the wrong one, it was incompatable.

I put the old thermostat back on, and the heat won't come on. As far as I can tell I didn't damage the old thermostat, and I'm sure everything is reconnected properly.

Is there something I need to know to re-start the heat pump?
Thanks,
donno13@hotmail.com On 2016-04-09 by donno13

Reply by (mod) -

First try resetting the equipment by turning the power off, waiting 5 minutes, and then turning it back on.

You can also eliminate the thermostat and it's wiring from the problem by disconnecting the two thermostat wires right at the heat pump.

Now if you jump over together the two thermostat terminals at the heat pump, that is the two terminals that should turn on the device, if it doesn't run the problem is there in a control board or relay.

Question: old Lennox compressor died, glowing red pipe - is there a contamination worry in the A/C system?

I have a very old Lennox compressor unit that died 2 days ago. WHen trying to determine what was wrong I turned on the unit from inside the house and when I went outside to inspect it the smell of burnt oil was in the air.

Then, when I looked at the condenser, the pipe looked like it was glowing red.

So, it's now time to change the unit. My question is would the pipe to my furnace and the A unit be contaminated with oil and other chemicals from the compressor?

Do I have to change the complete system, or can I simply replace the compressor unit? Thanks. - Pat 7/23/11

Reply:

Pat, in short, yes.

Your description of burnt oil smell and very hot A/C compressor parts is sure evidence of a motor burnup.

And you're right to worry about contaminants in the refrigeration system after a compressor motor crashes. Even the smallest amount of debris can clog the refrigerant metering device - thermal expansion valve or capillary tube.

A proper repair that involves replacing a compressor includes drawing a vacuum on the system for long enough to get as much contaminated material out as possible, and also the installation of a special compressor burnout drier filter on the system to catch remaining debris that would otherwise be circulating around in the refrigerant piping and coils.

This drier is discussed in more detail at the article REFRIGERANT DRIERS & FILTERS (links at the ARTICLE INDEX the bottom of this article )

Question: hard starting compressor

My A/C system is less than a year old.

When I turned on the A/C to check, the condensor unit comes on then shuts back off, then 30-45 seconds after comes on again for 2-5 seconds. Whats wrong? - Jon Anon

Compressor on Lennox central air not turning even if the thermostat is activated. It is blowing warm air.
Possible problem - Roger

Reply:

Roger: regarding your hard-starting compressor/condenser unit: we can't with confidence say what's wrong with so little information - your service tech can diagnose the problem, probably fairly quickly.

But a common cause of the symptoms you describe is a bad start/run capacitor or worse, a failing compressor motor.

Often, before replacing a hard starting AC compressor, the tech will try installing a hard-start capacitor to give the motor an extra "kick" to get it running. That can extend the life of the current system at a much lower cost than a complete replacement.

Watch out: But in my experience, a hard starting A/C compressor to which we add a hard start motor capacitor may work for a while longer, even a year or two, the truth is the motor is usually near end of life and the condenser/compressor system is likely to need replacement soon.

Todd said to Roger:

Roger...not a professional myself but I had the same issue.

The motor on my outside unit had worn out to the point that it needed to be replaced. Forturantely for me it was under warranty from a unit that I purchase 4-5 years ago. This might be strange for most units but we've had some above average summers here in Texas the last couple of years.

Another thing my HVAC tech does is check and replace the capacitor if necessary. I've been told that if the capacitor is shot, it will expand, almost resembling a coke can that is about to explode. Good luck.

Thanks Todd.

Roger, presuming you checked tonassure the unit has power and the thermostat is calling for cooling, if the suggestions in this article didn't get your system diagnosed check the LOST COOLING article linked above at the ARTICLE INDEX - Editor

 

Outdoor compressor takes too long to turn on - 10 minutes or more

Howdy, im no HVAC expert but I understand how it all works.

My problem is that the indoor blower comes on, the outdoor fan comes on, but the compressor seems to take a while to come on, sometimes up to 10 minutes, meanwhile its blowing non cold air around the house.

I go outside next to the compressor, when it comes on i hear the fan but not the compressor (no buzzing sound), but it does come on later and then the freon pipe gets cold and im all good.

I am in Miami and it is getting pretty hot here this summer, is this delay normal ?

Or is it a prelude to a more major issue ? - On 2018-08-08 by Paul

Reply by (mod) -

Paul,

The delay you described could be normal. For example in my office where we use a Sanyo split system air conditioner, the indoor blower unit may keep running at low speed but the outdoor compressor will turn on and off depending on when the control board (with its own computer) figures that it's needed.

That's an energy-saving feature.

But IF your AC blower is delivering warm air AND the room temperature is still above the thermostat setting, then yeah something's wrong, perhaps with a sensor or control relay on the unit.

That may not be a major repair cost ( a new compressor would be a major cost).

IF you hear the compressor humming but not starting, that's not very good and means there's a more serious problem. Call your service tech. I expect the technician will check temperature sensors and control boards in both the indoor air handler and outdoor compressor/condenser unit.

Let me know what you're told.

Question: Amana A/C compressor starts on 3rd or 4th try

Hi , The compressor on my 3 Ton Amana A/C unit starts after 5 minutes of fan start ( there is no delay relay ).

Ccold air blows out from top of the unit and looks like compressor tries to start couple of times and finally starts on 3-4 try and then it works normal . /10/14 PKG s

Reply:

PKG

Sounds like a hard-starting compressor, possibly a failing compressor motor, possibly aided for a time by a hard-start capacitor kit.

 

Compressor/Condenser Unit Runs then Stops

Diagnostic Starting Point:

• HVAC COMPRESSOR SHORT CYCLING ON & OFF

AC works for 5 minutes then seizes the compressor motor

My air conditioner works for 5 mins and seize my generator what could be the cause? - On 2019-03-17 by feasts

Reply by (mod) -

An A.C compressor that is no longer usable.

The underlying causes can be any of a variety of problems such as liquid refrigerant slugging, low voltage, control or switch failure, overheating, debris in refrigerant, etc. even age.

A/C system starts then shuts off

My AC unit during the hot and humid months here in FL, will not run without some help from me. Lets say it is 80 degrees and you set the thermostat at 75, it will run until temp drops about 3 degrees, then shuts off.

You then need to shut the unit off via the thermostat, for approximately 20-30 mins turn it back on in order for the air to start blowing again. I tried changing out the thermostat but this has not helped. What could be the problem? - (June 8, 2012) Renee said:

Reply by (mod) -

Renee, often when shutting off the A/C returns the delivery of cool air we trace that problem to frost formation on the cooling coil.

Click on FROST BUILD-UP on AIR CONDITIONER COILS check for, diagnose, & repair that problem. But first, make sure that your air filter is not debris clogged.

Question: air conditioner compressor shuts down after 30 minutes or less - short cycling HVAC compressor / condenser unit

My compressor shuts down after only 30 minutes or less, it starts fine, but cooling seems to be a bit less then before, and none at all once it shuts down. I open the breaker for a short time and it will run again, then shut down. - Darrell M 9/8/11

My a/c,compressor stars up and runs for 5 minutes before stopping,it's cooling for those 5 minutes it's running.I did replace the 50+5 cap. but it did not make a difference. (Aug 6, 2014) mike

Reply:

Darrell, it sounds as if a compressor motor may be overheating; when you leave power off for a time the motor cools down enough that its own internal thermal reset in fact resets itself.

I'd call a service technician for more thorough diagnosis.

By no cooling, if you mean there is airflow but the air is not cool, that's consistent with above.

Mike: Check for an overheating motor or a control board or relay snafu

See HVAC COMPRESSOR SHORT CYCLING ON & OFF

 

Question: compressor just runs for a few seconds, then cuts off; short cycling A/C compressor problems

My condenser starts for a few seconds then cuts off cycle continues - Anon.

my compressor fun has started to short cycle, it run for 2-3 min then shuts off for one second then restarts runs again then stops etc. with no funny sounds or noises - Don

Reply:

It's not clear from your question where in the entire cooling system your unit's troubles begin, so I'd look at diagnostic tips that may explain your compressor/condenser short cycling are found at LOST COOLING CAPACITY.

Certainly a compressor that is having trouble starting can be diagnosed at HARD STARTING COMPRESSOR MOTORS, if you're sure the trouble is outside.

Question: AC compressor shuts off after a few minutes

Please help, My AC compressor starts when I power it on and works perfectly but cuts off prematurely within 5 min. Compressor starts only after 2 hours however fan runs continuously. I also tried switching off and on but of no use.

Had there been a problem in the compressor, why its working fine for 5 minutes after approx every two hours. Also You can understand that within 5 minutes thermostat also can't cut as cooling of room is also partial. please help - Amit

Reply:

Amit

Possibly the motor is overheating, then binding, drawing high current, shutting down. Try cooling the outdoor unit with a water spray.

If cooling the outdoor unit (designed to tolerate rainfall) changes its operation that is probably a diagnostic clue.

 

Question: Our new AC won't keep running - the compressor keeps turning off and on

My A/C compressor broke about two weeks ago, we got a new one but when the fan starts the compressor works for a while and then it shuts down, and its turning on and off and I dont know whats wrong - Help.

Reply:

Help: if your new A/c won't keep running after it has just been installed, surely you should call the installer and expect it to be repaired under warranty - it's just been two weeks.

Even if all of the new equipment is in good condition, an example of a problem that could occur during compressor replacement is that contamination, moisture, dirt in the refrigeration system (which is made worse if a compressor burns up) can interfere with proper system operation.

Compressor / Condenser Unit Won't Stop Running

Diagnostic Starting Point:

• COMPRESSOR / CONDENSER DIAGNOSTICS - home
• HEAT WON'T TURN OFF - if your heat pump is in HEAT mode
• HVAC COMPRESSOR WON'T STOP

Question: how long should an air conditioner compressor run before it cycles off?

Hi. How long should my ac compressor keep on running before it automatically turns off. - Mon 5/31/12

Reply: it depends...

Mon: about typical air conditioning compressor run time, I don't think there is a single right answer to your question, because the on-cycle time depends on several variables that could in some cases leave the unit on for a long time, even continuously. Those variables that set the run time for the compressor include

- the indoor temperature, that is in turn affected by outdoor temperature and sunlight as well as building heat gain, windows, insulation, air leakage, and similar factors

- the thermostat set point - if the thermostat is set to a cooling number below what the system can achieve it will run continuously

- the size or capacity of the cooling system versus the actual building cooling load

However there is another way to approach your question that may be more useful diagnostically. That is to ask if something has changed in how your A/C system seems to operate.

So if you think that the building and its insulation, windows, heat gain conditions have not changed, and if your thermostat setting is the same temperature as in previous cooling seasons, and if the outdoor temperature and sun and wind conditions are similar to previous seasons, and THEN if your cooling system seems to run longer or continuously when it did not previously, there may be a problem to diagnose and repair.

Check the LOST COOLING CAPACITY article (links at the ARTICLE INDEX the bottom of this article ) for more detailed diagnostic suggestions.

Question: how long should the AC run when first turned on?

Anon said

when you turn on the AC for the first day of summer or heat how long would the unit circulate air then when does it stop

Reply:

The length of time that the A/C will run depends on many factors including

- the thermostat set temperature

- the building temperature at time the A/C is tuned on

- the efficiency of and cooling power (BTUS) of the system

- where the air is delivered

- thermostat location

- the thermal mass of the building: what materials have been heated up and need to be cooled down

- the heat gain rate of the building

- outdoor temperature, wind, and sun exposure

The air will circulate and the A/C will run until the thermostat is satisified. If the system cannot satisfy the thermostat for any reason the system will keep running.

Question: air conditioner or heat pump compressor / condenser won't shut off

My air conditioner compressor keeps running even when I put the thermostat on heat.

I just had a new furnace installed this winter and there are two wires coming from the compressor one is red and one is white.

I connected the whit to the letter "C" on the furnace and the red to the red wire.

I tried to connect the white wire to the yellow, green and white wires but the compressor would not energize.

When I connected the white wire to the "C" contact in the furnace the compressor came on runs fine and puts out cold air but will not shut down when I switch to heat? (Apr 29, 2015) Raymond

Reply:

First check that the thermostat is set above room temperature or is in the OFF position.

Then check your thermostat wiring connections to the control board in the air handler against the IO manual wiring instructions or wiring diagram.

Or for more help see THERMOSTAT WIRE CONNECTIONS - how to wire up all types and brands of heating & cooling thermostats

Then see COMPRESSOR / CONDENSER DIAGNOSTICS where we include HVAC COMPRESSOR WON'T STOP

Heat pump in heat mode won't turn off

AC side works good air out @ 59-60 deg. When I switch to heat emergency heat mode, the heat comes on & blows hot air & goes well beyond set point & wont shut off until I shut it off . I'm mot much good @ computers so help me if you can Thanks - On 2020-11-11 by tom -

Reply by (mod) -

Tom

When cooling works and heating mode does not I suspect a control board or reversing valve problem. That's what your service tech will probably check; it's not something a homeowner would try.

Most likely a control is turning on your backup heat and not turning it off - you're stuck in heat mode.

See the diagnostic steps at BACKUP HEAT for HEAT PUMPS 

Question: My A/C compressor just won't stop running

I recently noticed my AC condenser unit still running when the system inside shutoff by itself. and also, does the condenser unit have to be leveled. I notice the slap which holding the unit is slopping. Any suggestions? Thank you. - Rick 8/16/11

Reply:

A/C compressor/condenser won't stop running:

Rick usually when an A/C condenser unit won't stop running even though the inside equipment has shut off by itself my thinking divides into two investigations:

- is there a problem with the INDOOR unit such as a blower fan that won't start, an access door switch open, a condensate drain switch turning off the blower unit - these can leave the system calling for heat and the compressor running (though that's not good for the compressor)

- is there a problem with the outdoor equipment such as a bad control relay or control board

See COMPRESSOR / CONDENSER DIAGNOSTICS

 

Question: My A/C compressor just won't stop running

I recently noticed my AC condenser unit still running when the system inside shutoff by itself. and also, does the condenser unit have to be leveled.

I notice the slap which holding the unit is slopping. Any suggestions? Thank you. - Rick 8/16/11

Reply:

A/C compressor/condenser won't stop running:

Rick usually when an A/C condenser unit won't stop running even though the inside equipment has shut off by itself my thinking divides into two investigations:

- is there a problem with the INDOOR unit such as a blower fan that won't start, an access door switch open, a condensate drain switch turning off the blower unit - these can leave the system calling for heat and the compressor running (though that's not good for the compressor)

- is there a problem with the outdoor equipment such as a bad control relay or control board

And yes the compressor/condenser unit should be level or close to level.

 

My Central Heating System Won't Turn Off

My central heat continuously run and does not shut off when it reach the temperature set on thermostat what could this be it - On 2018-10-27 by Gloria -

Reply by (mod) - What to do if heat pump won't shut off

Gloria

When your central heating won't turn off regardless of what you do at the thermostat, that's probably not a heat pump or compressor/condenser unit problem.

Instead, see the diagnostic steps at HEAT WON'T TURN OFF

 

Split AC takes too long to reach indoor temperature setting

Sometime my split ac take more than 2 hours to reach 24 degree temp sometime it achieved in a hour. However in each cycle compressor remain off for 2-3 minutes..

I suspect shutdown time between cycle is very less. Is it supposed to be 2-3 minutes only? - On 2020-05-08 by Raud

Reply by (mod) -

If the outdoor conditions and the buildings rate of heat loss or heat gain is more or less the same then I would agree that that much variation in cycle time for your heat pump suggests that something is wrong.

I would expect your service technician to check for a failing or sticking thermostatic expansion valve or a failing or sticking control relay.

Followup by Raud

Thank you for quick reply..

Unfortunately in my area no expert technician.. Outside temperature is 33..my room is on top floor.. Two window and two door cover by curtain.... In this case 2-3 minutes shutdown time is less right? Per hour how much minutes it should stay shutdown..

Reply by (mod) -

Raud

There's no "right" answer to the on-off cycle time for an AC or heat pump system as the big variables swing just too widely:

- outdoor temperature
- building heat gain or loss rate, including windows, air leaks, insulation, etc.
- efficiency of the whole system, including ductwork, fans, registers, etc.

Even a dirty filter will make a big difference in air flow and run times.

It's the wide cycle time variation that you cited that made me think the system needs repair.

Frost or Icing at the Outdoor Compressor/Condenser

My air conditioner compressor blew, the new system is icing up, what's going on?

I am a 100% service-connected disabled veteran who just spent over $3700. to replace a 4 ton trane xr12 air conditioner condenser and coil. My old condenser compressor blew up and the HVAC guy said it wasn't worth replacing since the unit was a 9 yr old r-22 system.

He talked me into a new trane xr13, 4 ton, r-410 condenser and a 5 ton evaporative coil for an extra $400. saying I'd get 10% more cooling capacity than the 4 ton coil. this was 5 weeks ago. three techs have been here since trying to figure out why the evaporative coil keeps icing up.

the best cooling we get with the thermostat set at 72 degrees is only 15 degrees cooler than it is outside.this is with the front panel off the furnace.

With the panel in place, in 2 or 3 days the coil turns into a block of ice. even with the panel off, as the day wears on and the outside temperature drops, the inside temperature increases. right now, the thermostat is at 72, it's10:15 p.m. it's 73 degrees outside and 76 degrees inside.

The HVAC guys tried to blame my ductwork as unable to handle the airflow, then inadequate air returns, then too small a hole (10x12) above the coil going to the plenum. all solutions of course would require a 2nd mortgage.

My response was . BULL. It's something they did wrong because before the compressor blew, if the outside temperature was 100 degrees, inside it was 78 degrees.(with the thermostat set at 72.

Not once in 9 years did it ice up or did I ever have to remove the front panel of the furnace to increase the airflow., It has to be one or both of the things they installed, like maybe a defective evaporator coil. Do you have any suggestions? Thanks - B.H.

Reply:

Cooling coil icing can be due to an improper refrigerant charge, inadequate air flow across the cooling coil, or a problem with a refrigerant metering device (or something else we haven't thought-of).

Your HVAC guys might be right that your old duct system is not moving enough air across the coil, allowing it to ice up, but if that's the problem I'd ask them why they didn't think of that before selling you that extra big evaporative coil in the air handler.

In a good-working air conditioner or heat pump system the components need to be in balance: compressor/condenser, air handler/evaporator, and ductwork.

If we hold off on the blame game for a bit, let's see if you can increase the airflow across the coil.

Often I find on older cooling systems that the return air opening was too small or the connections from return register to the air handler small or cramped or twisty.

A very crude "test" that I do NOT RECOMMEND for more than a few minutes of test operation is to see if the coil ices up if someone leaves the air handler blower compartment door off - to maximize the return air opening.

Take a look under DUCT SYSTEM DESIGN SIZE & DEFECTS for the article

: RETURN AIR REGISTERS & DUCTS,

and also take a look at COOLING COIL or EVAPORATOR COIL

and at the article:

FROST BUILD-UP on AIR CONDITIONER COILS for more help.

Finally, at RETROFIT SIZING for A/C or HEAT PUMPS we touch on the importance of balancing the system components during a retrofit or upgrade of an air conditioner or heat pump system.

Let us know what you find - we'll both learn something.

Question: ice on the refrigerant line, no cooling in the house

My line set going to outdoor unit has ice on it. Lost cooling in house. What is the problem and is there anything I can do to fix the issue - Pat

Reply: check the indoor air handler for an ice-blocked coil

A problem with a refrigerant metering device (thermostatic expansion valve, capillary tube, etc), or even a dirty air filter can lead to improper metering of refrigerant into the indoor cooling coil, leading to icing; but other causes of ice formation include an improper refrigerant charge or even something as simple as missing refrigerant line insulation.

But when you also lose cooling inside, I suspect an ice blocked coil.

See FROST BUILD-UP on AIR CONDITIONER COILS

Question: how does a low refrigerant charge cause the coil to ice-up

How does a low amount of refrigerant entering the evaporator coil cause it to ice up? Bob

Reply:

Bob, low refrigerant means too little in the cooling coil, lower evaporation temperatures, ice formation. Details of the explanation begin at

FROST BUILD-UP on AIR CONDITIONER COILS

And at REPAIRS for FROST / ICE on COIL we include a more technical explanation titled

Reader Question: why does a low refrigerant charge cause frost to show up on the coil ?

Question: Icing at the compressor; compressor not turning on?

the outside unit of the heat pump is icing up on the compressor - Steve 8/7/11

Hi my fan in my house goes on but my compressor unit does not all the electric seems to be fine . could it be my thermostat? - Sam 8/7/11

the accu very heat,although it is new gen. clean,2Tr LS-60psi & HS-100psi, - Anon 8/6/11

Reply:

Steve: icing at the compressor/condenser sounds like a refrigerant charger or refrigerant metering problem.

Sam: if your thermostat turns on the air handler but the compressor/condenser does not run, the problem is not the thermostat. Check out the diagnostic suggestiosn beginning at LOST COOLING CAPACITY (link at the ARTICLE INDEX the bottom of this article )

Anon: those pressures look kind of low, no? What does your HVAC tech say about normal for that system?

Question: ice on the refrigerant line, no cooling in the house

My line set going to outdoor unit has ice on it. Lost cooling in house. What is the problem and is there anything I can do to fix the issue - Pat

Reply: check the indoor air handler for an ice-blocked coil

A problem with a refrigerant metering device (thermostatic expansion valve, capillary tube, etc), or even a dirty air filter can lead to improper metering of refrigerant into the indoor cooling coil, leading to icing; but other causes of ice formation include an improper refrigerant charge or even something as simple as missing refrigerant line insulation. But when you also lose cooling inside, I suspect an ice blocked coil.

See FROST BUILD-UP on AIR CONDITIONER COILS

Question: ice build up inside the ductwork

I have ice build up on the inside of the furnace duct work. This will plug up the lines and the fans will not circulate thus stop blowing cold air

Reply:

If you find ice build-up inside the ductwork itself that's pretty unusual except in winter in freezing climates when moist air is rising into the duct system. Usually ice forms at the cooling coil in an air conditioner air handler or blower unit.

But I agree that ice can block air flow and more, when it melts, can cause water damage or even a mold problem in the building.

For more detailed advice please see WATER & ICE IN DUCT WORK.

To diagnose and fix ice formation on the cooling coil itself, see FROST BUILD-UP on AIR CONDITIONER COILS

Question: replaced air conditioner compressor, new system is icing up

Question: My air conditioner compressor blew, the new system is icing up, what's going on? add another return to it .

may have to change duct size maynot if indoor unit is close to returns . hope that helps a bit - Chris 3/15/12

Reply:

Rooster said:

Sounds like you may have put a 1500HP Blown Hemi in a Volkswagen. One thing to try...did the installer select the proper fan speed for the air handler? If the fan is running in a slower speed (usually for heating, not A/C), air flow will be inadequate. But I'm betting on inadequate duct capacity.

Probably should have stuck with the 4 ton evaporator coil. Sounds like an oversight or ignorance on the installers part to me.

Also see COOLING COIL or EVAPORATOR COIL for our article on causes of cooling coil ice problems. Something as simple as a dirty filter or blower fan can cause the trouble.

The Haier AC unit is forming frost or ice on the coil

my question is I have turned off my 1 ton haier ac its inner unit is shut off but not outer unit due to which it it creates ice in inner unit can you let me know what is the issue. Thanks !! - Asim Niaz 9/15/11

Reply:

Asim, if the indoor blower unit is not running and the outdoor compressor is running the lack of air movement across the evaporator coil will lead to frost and ice formation on the coil.

A TEV can jam from dirt and debris or other contaminants including moisture that can actually freeze in a TEV. It's not a part you can change out yourself.

Under COOLING COIL or EVAPORATOR COIL you'll find diagnosis of ice or frost blocked cooling coils.

Question: Icing at the compressor; compressor not turning on?

the outside unit of the heat pump is icing up on the compressor - Steve 8/7/11

Hi my fan in my house goes on but my compressor unit does not all the electric seems to be fine . could it be my thermostat? - Sam 8/7/11

the accu very heat,although it is new gen. clean,2Tr LS-60psi & HS-100psi, - Anon 8/6/11

Reply:

Steve: icing at the compressor/condenser sounds like a refrigerant charger or refrigerant metering problem.

Sam: if your thermostat turns on the air handler but the compressor/condenser does not run, the problem is not the thermostat. Check out the diagnostic suggestiosn beginning at LOST COOLING CAPACITY (link at the ARTICLE INDEX the bottom of this article )

Anon: those pressures look kind of low, no? What does your HVAC tech say about normal for that system?

Compressor/Condenser HVAC Oil Lubricant Problems

Question: oil in the capillary tube? - recurrent cap tube clogging

i have replaced my compressor from company and when I started it was giving cool air but the copper pipe out side (large) was not cool enough and after 40 mints its timer light flashes and after 10 more mints its down automatically. it happens again and again I sent back it to company technician is looking into it.

He said oil was in capillary and it needs flushing so he will replace its capilary since after cleaning its not fixed. do u think there is no fault in compressor? or what possibly is the problem.. - Wagar 7/11/12

Reply:

You'll want to check the installation manual to find the control light decoding for your brand and model of cooling equipment. Could be a control or control board problem too. It's just about impossible to flush a cap tube so replacement is normal.

But if there is debris in the system, or excessive oil, the new cap can clog as well; good practice would be to empty the system, pull a vacuum, flush the whole system, install a filter dryer, replace the cap tube, and recharge.

Question: can the condenser get oil logged

Can a condenser become oil logged, how and why? - Dominic 8/22/11

Reply:

Dominic:

A condenser, if you mean the condensing coil, set level, would not be expected itself to become oil clogged, though condensers do sometimes clog from a combination of debris and moisture or oil.

But refrigerant oil moving through the system can clog a refrigerant metering device such as a capillary tube.

Dom, it is normal for some refrigerant oil to circulate through the HVAC refrigeration system;

Oil clogging can occur in some installations if the refrigerant piping is not properly routed or due to an improper charge.

The more usual problem is not at the condenser coil but at smaller orifices such as a cap tube or the TEV.

See

• COMPRESSOR / CONDENSER OILS