Outside unit fan and compressor will run for about 10 seconds, then shut off with a loud clicking noise. After about 10 seconds they will start again and run for about 5 seconds, then shut off. Googling around I find various possible causes like bad motor, contactor, defrost sensor, bad compressor, low on refrigerant. I checked the 40+5 capacitor and it read 32, so I replaced it, but still had same problem. Any ideas on what is the likely problem. I am going to check the motor resistance on its 3 leads tomorrow evening. The Carrier 38EZA024 311 is 12 years old. The motor is rusted on the exterior sides, but the blades seem to turn freely. But would it be a fan motor problem if the compressor goes off at same time as the fan stops?

 

My first choice would be low on refrigerant.
The low pressure switch opens the 24v contactor line shutting off both fan and compressor.

 

Thanks. Haven't done anything to this one since buying the house 4 years ago. Does low refrigerant always mean a leak somewhere?

 

An A/C system is a closed system. Ideally, it should never require adding refrigerant. If it is low on refrigerant, it means that there is a leak somewhere. There is a simple way to determine if the short cycling is due to the low pressure switch opening (low refrigerant charge). If you can find the low pressure switch (it will be in the outside unit), just temporarily jumper it. If the compressor now runs longer than 5 seconds, the pressure is low and the system is likely low on refrigerant. Don't let the compressor run for any length of time if it's low on refrigerant, as that can damage the compressor. Just let it run long enough to see if it's longer than the current 5 seconds. I would suggest letting it run for only 15 seconds or so.

 

When the compressor is cold (has not run and allowed to cool of a while) and you start it, does it run for a longer period?

If so, this would mean the overheat protection sensor is shutting down the compressor because it is overheating.

Low refrigerant could cause this... internal compressor problem also could do that.

I would check the compressor winding (plenty of video on youtube on how to do this) if it checks OK then you likely have a leak and lost refrigerant and that is causing the compressor to start and stop.

 

This doesn't appear to be a compressor problem. OP stated the fan and compressor turn off together.

What must be established is if the contactor is opening.
Then it needs to be established why it's opening.

 

I did some more checking tonite. Voltages on the 3 sections of the contactor were good. Contactor looks to be in decent shape. With outside switch off, and thermostat on, relay stays pushed in. Is the low pressure switch the small device on the suction line inside the outside unit? There seems to be some oily leak on the bottom underneath it. Not a lot, but enough to lightly cover that section of the bottom.
I took the fan off the top and it seemed to be ok, not loose, turns fine. The compressor has been off for several days. Only turned on when I'm checking it. I turn it off after it tries starting twice. The inside blower runs fine. No water leaking on inside. Anything else I can check before calling the repairman? Would a new contactor or a hard-start kit be worth trying? Should I let it try starting more than twice to see if it eventually stays on?

 

Yes.... you can disconnect the wires from the switch and short them together. The compressor should continue to run. Don't try that for more than 20 seconds.

You can also put a voltmeter across those two switch terminals. If you see voltage (24vac) on them when the compressor shuts off.... you've found the problem.

An oil puddle under that switch is a sign it may be leaking refrigerant there.

 

ok, thanks. Rain next few days, so will not be able to do anything until this weekend probably.

 

Repairman came and added 4 pounds R410 (capacity 5 pounds) and it is running fine now. He had a leak detector but didn't find anything.