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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 Problem FAQs #4

Diagnose Air Conditioners & Heat Pump Compressor/Condenser unit problems

Air Conditioning & Heat Pump FAQs Set #4

Questions & answers about fixing problems with air conditioners & heat pumps posted by readers at the A/C or heat pump diagnostic home page.

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Air Conditioning & Heat Pump Troubleshooting FAQs-4

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 GUIDE A/C or HEAT PUMP.

Also see this list of A/C & Heat Pump Diagnostic FAQs sorted by major topic at AIR CONDITIONING & HEAT PUMP SYSTEM FAQs

Article Contents

 

HVAC System Capacitor Diagnostic FAQs

Replacing compressor capacitor didn't fix the trouble

I replaced the 50/3 MFD capacitor with a new one. Noticed the outside compressor fan running at half-speed as before when the indoor TT is set to OFF (yes, it's baffling).

As soon as the indoor TT was switched to ON, the fan spun to full speed, then the 30Amp breaker tripped immediately (maybe due to compressor malfunction).

Was hoping the new capacitor would resolve the issue, but looks like seized compressor and/or a bad controls in the outdoor compressor/condenser unit as you mentioned. Thanks again for your help. - On 2011-07-09 by TN-Goose -

Moderator reply:

Before launching into a compressor replacement, I'd want help from an on-site HVAC repair technician who can check the current compressor's operation, current draw, and staring trouble.

Particularly I'd also want to check the control relay and board, and I'd check the compressor's current draw for signs of a failing electric motor.

Also see CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS

and CAPACITOR FAQs

 

Refrigerant Undercharge or Overcharge Effects on Compressor FAQs

Can a lack of refrigerant stop theA/C compressor from running?

I have an A/C system that is no longer cooling. The serviceman came out and said we needed a new compressor. He stopped by to drain Freon/r22 or what ever cooling agent but said there was none in the system.

Can a lack of cooling agent stop the compressor from running? - On 2011-07-08 by Ken -

Reply by (mod) - A lack of refrigerant will not stop a compressor motor from running right away but pretty soon it will ruin the motor due to lack of lubricant

A lack of refreigerant will not stop a compressor motor from running, the motor will run but if there is too little or no refrigerant gas (in your case Freon R22 which is obsolete) the system just won't cool the air blown across the evaporator coil.

But because refrigerant also includes a lubricant needed by the compressor, if your system loses all of its refrigerant and the compressor motor keeps running, yes it may be ruined by lack of proper lubrication.

You need a new compressor if the old one is seized or if it is so worn that it won't compress the refrigerant gas. If your system is not cooling because it's lost refrigerant, it may be possible to re-charge it. Ask for specifics of how the tech knew the problem is the compressor.

 

Can a refrigerant overcharge Ruin a Compressor?

A service tech left my air conditioner with a huge overcharge according to the next guy who came to my house to fix it. The second guy says the first guy killed my compressor motor.

Can a refrigerant overcharge ruin an air conditioning compressor? - Michael

Reply by (mod) - Yes!

Michael:

Can a refrigerant overcharge ruin an air conditioning compressor? Sure. Liquid slugging - liquid refrigerant from an overcharge can enter the compressor motor.

I'm not expert enough to make a general comment about ALL A/C compressors, but certainly there are some designs in which an overcharge that sends liquid refrigerant into the compressor piston or valve area can ruin it promptly.

Imagine a piston trying to move in a cylinder that has liquid in it where just compressible gas is supposed to be found.

 

 

Effect of TEV on Compressor Operation FAQs

HVAC tech discusses repairing a Coolair Split Unit - one compressor unit is not cooling

I'm working on a coolair split unit with 2 evaporator's 1condenser and 2 compressor's all fan belt's and condenser belt are good .

All filter's were changed, one of the evaporator section is discharging 55deg air at 86deg outside temp and gauge pressures of 65/245 and the other evaporator unit at 86deg out side temp is discharging 64deg with pressures of 78/265 can you help - 2011-07-07 by tony -

Reply by (mod) -

Tony: Those pressures for the two units are both practically in the same range.

It's possible that the TEV adjustments are not identical on the two units. Did you check the TEV (Thermal expansion valve) ?

 

Return Air FAQs

Why is return air being taken from my garage? Garage is too hot.

Why am I getting return air for my HVAC from garage ceiling .air is so hot in garage area - On 2011-07-03 by al entez -

Reply by (mod) - block off unwanted return air but check the total return air adequacy too

Al, if your garage is not being cooled AND if there is adequate return air supply from the rest of your building, you can simply block off that garage return-air inlet. That's what I'd do.

But be sure that you've got enough return air elsewhere in the system.

See RETURN AIR, HVAC

 

 

 

A/C Electrical issues: current draw, high amps FAQs

Air Conditioner / Heat Pump Current Draw Issues

If the compressor is rated for 14Amp and is running at 11.8 Amp dose this mean the compressor is ready to burn out?

If the compressor is rated for 14Amp and is running at 11.8 Amp dose this mean the compressor is ready to burn out? - On 2011-06-17 by jim

Reply by (mod) - no

Jim:

About your question "If the compressor is rated for 14Amp and is running at 11.8 Amp dose this mean the compressor is ready to burn out?"

Not in my book. Usually when a compressor is seizing up it will draw abnormally high amps not lower amps. Take a look at the RLA figure for your unit.

Follow-up comment by jman

To jim no that the rating for design conditions was the temp outside 95 if not then it is good

Followup by jim Hanlon

Jman the outside temp was over 95

Compressor has failed mechanically (drawing far too many amps).

Just a follow-up for future readers. Compressor has failed mechanically (drawing far too many amps).

My no-name (builder grade) outside unit trys to start but won't. The fan runs fine (I replaced it last year)but the compressor tries to start for about 2 seconds, then stops. About 45 seconds later it will try again. Same results. It never trips the breaker.

I had a tech come out while I was at work and he "thinks" the compressor is locked up. I checked the resistance today and got .001 C-R, .002 C-S, and .002 R-S. My DMM reads OL (overlimit) when checking all three terminals against the compressor case. I'm leaning toward low refrigerant (is there a low pressure shut-off on home systems like in cars?).

Tech that came out told the wife it wasn't low on refrigerant but...? I'm gonna swap a known-good Run-start cap from my other unit and try that. I guess the compressor could've failed mechanically. Any thoughts? - On 2011-06-06 by Richard -

Reply by (mod) - a high amp draw on the compressor circuit

Thanks Richard for the followup A/C diagnostic detail. Indeed a high amp draw on the compressor circuit is one of the basic diagnostic tests that lead a tech to think the unit is seized or failing.

The high pressure (smaller diameter) refrigerant line is not normally cold in cooling mode but could be warm or even hot depending on where along its length you are checking on its temperature.

The low pressure or suction line (the larger diameter refrigerant line) is normally cold when the air conditioner has been running for a while and can even show frost on uninsulated sections.

I'm not sure from your description if I can say that the high pressure warm line is a problem, but if your low pressure line is never getting cold I suspect a lost refrigerant charge (or the compressor is not running at all).

Air Conditioner Compressor trips the breaker

The outside compressor/condenser unit of my central air conditioner, which is wired to a bi-pole 30amp circuit breaker, started to trip the breaker whenever the indoor thermostat turns ON the air conditioner. Never had this issue in the past 6 yrs.

Despite the breaker being tripped, there's air coming out of the supply registers, but it's warm obviously due to the compressor/condenser unit being tripped OFF.

What could be some reasons for tripping the breaker? One strange condition I noticed is that when the indoor thermostat is switched to OFF (not on Cool), the breaker stays ON without tripping, and the compressor/condenser unit's fan rotates at about medium speed, instead of being OFF.

Any suggestions or help will be appreciated. - On 2011-06-04 by TN_Goose

Reply by (mod) - Check current draw at the compressor and check possible bad control board

TN_Goose:

It sounds as if your outside compressor/condenser is not starting; a compressor that has seized or is drawing high amps would trip the breaker.

I'm baffled about why the outside compressor fan would run at all when the indoor TT is set to OFF; could be a bad control board or circuit or one that was damaged during compressor burnup.

Followup by TN_Goose What would cause the compressor to seize or burnup?

Thank you for the quick reply. When you say "bad control board or circuit", are you referring to the ones in the compressor/condenser or TT?

Would a faulty capacitor (one that might be almost ready to fail) cause the compressor fan to run? It's really odd for the fan to run with TT set to OFF. I opened the outer casing of the compressor/condenser today and checked the apprearance of the capacitor (looks fine - .no bulging or corrosion anywhere...couldn't check for the MFD

Waiting on the just purchased HVAC/R multimeter shipment), and all wiring connections from the compressor and the fan look OK (no shorting or loose connection).

What would cause the compressor to seize or burnup? I'm wondering if the extreme hail storm and heavy rain that partially flooded outside compressor/condenser area (about 3-inches of water) has anything to do with it.

Reply by (mod) - seized motor: bad bearing, liquid slugging, bad lubrication, wrong voltage, other causes of A/C compressor failure

Typically for the symptoms you described, if it's not a thermostat problem, the service tech will probably do some simple electrical tests of the compressor/condenser unit, check system pressures, and will visually examine the controls and circuits in the outdoor compressor/condenser unit for an obvious problem before doing more sophisticated tests.

FYI sometimes a capacitor can be bad without bulging.

Compressors can seize from internal wear, a problem that can be accelerated if there is moisture or if there are contaminants in the refrigerant.

Followup by TN_Goose - check the start capacitor first

I'm going to check the capacitor MFD first, then if it's not the capacitor issue, I'm going to call Hiller Air Condtioning. I'll post the result of the root cause finding. Thanks again for your help.


Goodman Janitrol unit fan makes buzzing sound and doesn't spin

My Goodman Janitrol 2 ton turns on but the fan just makes a "buzzing" sound instead of spinning. - On 2011-06-05 by Jeff - J

Moderator reply: If your A/C is buzzing

Your fan motor may be shot or there can be a control board problem - the service tech might first try replacing the fan motor capacitor(s).

If your A/C fan is buzzing but not spinning my first guess would be that the motor is burned up or perhaps easier, the motor needs a starting or start/run capacitor. Under COMPRESSOR & CONDENSING COIL, A/C check out the article titled CAPACITORS for HARD STARTING MOTORS (see links(links found at the ARTICLE INDEX near the end of this page) ).

 

Replaced Goodman A/C unit after refrigerant loss: now got a bad compressor motor?

Have Goodman home unit with R22 about ten years old. Compressor replaced 5 years, one month ago (out of warranty). Evaporator core recently replaced due to leaks, and unit has not worked properly since providing minimal cooling.

With outside temperature of 95, have head pressure of 210 and suction pressure of 118. Suction line is sweating at the core and outside but little cooling. I am being told that the compressor is bad.

Could something have happened during the evaporator core replacement to cause this, or could there be a problem with the new evaporator core.

As the homeowner I am suggesting evacuating and recharge but this may be a futile exercise. Other causes have been ruled out (i.e. airflow okay, no freezing up, etc.) - On 2011-06-04 by Pahugh

Reply by (mod) - pressure readings may indeed indicate that the compressor has lost an internal seal

Pahugh:

I'm not sure, but those pressure readings may indeed indicate that the compressor has lost an internal seal or has a bad internal valve. Before replacing the compressor you need to ask what refrigerant was used to recharge your system when it was last repaired.

Putting a new A/C refrigerant into an older unit that was designed for a different refrigerant wont' work properly.

 

Refrigerant line temperature FAQs

Refrigerant lines not cold, compressor makes GRR noises and is not running

There is no ice on any lines -- there not even cold. I went out there and turned it on again. But this time I listened.

I heard the compressor make a gr sound then a min or 2 later a GRR sound again then never made noise after that. Anyone have any idea. My recent post is 6 days prior to this one. - On 2011-06-15 by Andrew -

Comment by TN-Goose

To Andrew: while troubleshooting my compressor/condenser unit problem, I came across a tip that said that some special capacitor, called hard start capacitor, can be added to give a boost start to the compressor (especially older ones that are hard to start). It said the hard start capacitors are a combination of a capacitor and a built-in relay. Supposedly, they are inexpensive.

 

Ice on the suction line at the condenser Unit

Ice on the return line at the condenser? - On 2011-06-11 by Herb M. -

Reply by (mod)

Sounds like you're missing refrigerant line insulation. See

REFRIGERANT PIPING INSULATION

Compressor Condenser Unit Suction line gets warm to the touch

After my condenser is turned on for about 4 minutes the suction line starts to get warm to the touch. can you tell me what the problem may be - On 2011-05-27 by JMONTE -

Reply by (mod) -

JMONTE:
If the HVAC suction line gets warm, you may be out of refrigerant, or the system may be running in heating mode if it's a heat pump.

 

Short Cycling Compressor Unit FAQs

Compressor short-cycles on and of every few seconds or minutes.

Are compressor cycles on and of every few seconds or minutes. What can we do to fix this systems not even a year old - On 2011-05-30 by matthew -

A/C compressor short cycling every 10 seconds!

I have the same problem as Matthew: my compressor cycles on and of every ~10 seconds. I is about 5yr old. What can we do to fix this system. Please help. Thanks! - On 2011-05-31 by Joe -

Reply by (mod) - causes of a home air conditioner compressor short cycling on and off too rapidly

Some causes of a home air conditioner compressor short cycling on and off too rapidly include these:

1. loss of refrigerant - a refrigerant leak in the system. You may be able to repair the short cycling problem temporarily by recharging the system but the proper repair is to find and fix the leak.

2. coil icing: the evaporator coil (cooling coil) is iced over (such as due to improper refrigerant charge or dirt or a reduced air flow due to a dirty filter) - take a look in the air handler to see if the coil is blocked by ice or dirt.

3. oversized air conditioner: if the short cycling has always been a problem since the day the system was installed, there is a good chance that the unit is too big (too many BTUS) for the space being cooled.

A more subtle version of this same problem is that you've done something like closing doors or adding a partition that had the effect of reducing the size of the space being cooled.

Sometimes we can mitigate this problem by running the blower fan at a lower speed or by opening interior doors to increase the size of the space being cooled or even by moving the thermostat.

 

Thank you to our readers for their generous comments

THANKS FOR YOUR RESPONSE!
...THIS IS SO COOL!! Have to tell my friends about you! - On 2011-06-08 by Livvy

Cool website thanks - On 2011-05-28 by jay

Thanks for so much info. been a big help. more power! - On 2011-06-17 by robert

Reply by (mod) -

Thanks for the Kudos and encouragement. We've worked hard on this material for over twenty years so we're very grateful when readers find it useful and trusted.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles.

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