Air conditioner compressor trouble starting

[TonyK]

Just after any thoughts on this one.

I have an aging "box" type 2hp air conditioner that I'm planning to replace in a few months with a split system. It's about 20 years old so it's seen it's day. If powered up cold it cools ok but when the thermostat cuts the compressor it fails to restart it several minutes later. You can hear a brief hum accompanied by the fan slowing a little at it tries to start the compressor. It gives up and tries again at intervals without success. Might get lucky half an hour later though. Reading here and there, the general concensus may be an AC capacitor for the compressor may be failing or even the compressor itself but bear in mind it runs fine from a cold start and continues to run just fine until that first thermostat cycle.

I had a thought of cutting off the temperature sensor sitting in front of the evaporator and measuring it's "hot day" resistance ( yes it's an electronic temperature control) then selecting and replacing it with a suitable fixed resistor. This theroretically will make the compressor run continuously but at least give us some cool time when we need it and keep it usable until we throw it out.

Any thoughts on my logic here ?

Regards, Tony

[Tony Hwang]

Hi, Starting cap or centrifugal contacts inside motor?

[Big Al]

You're thinking he has a belt drive compressor:) He should just try a hard start kit.

Al

[Stormin Mormon]

Typically, this is low electrical voltage. Clean the blades on the plug (emery cloth) till they are bright. Consider having an electrician replace the electrical socket. Have him (her) wrap the wires around the screws, not back stab the outlet.

I've heard this symptom many, many times. It's generally bad contacts on the plug, and resulting low voltage.