Hard Starting A/C & Heat Pump Outside Compressor/Condenser Unit FAQs

Hard starting compressor unit
Hard starting compressor motor
Hard starting condenser fan motor

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 this

LOST COOLING CAPACITY

diagnostic article

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.