Air Conditioning - A/C problem

Hello. I have two separate 3 ton RHEEM a/c condensers that are around 10 YO. One for the upper half of my house and one
for the lower half. I’m running two separate FAU’s. It’s been real hot here in southern California lately, and I ran both a/c ‘s
simultaneously. I usually run just the upper a/c, and this is the first time in a year both were run. The problem I had was while
they were both on, the upper a/c started blowing out warm air from the ducts. The condenser fan was turning as usual but
the air coming off the condenser was not warm like it usually was. Lower a/c was fine throughout all of this. When I tried the
upper a/c the next day, it was working fine again. Anyone have any ideas what happened here?

Hard to say for sure without being there. But it sounds like the compressor shut down (the condenser fan will continue to run). The likely cause is compressor overheating or overload. This can be caused by a bad capacitor, low refrigerant, dirty coils or even a restriction in the refrigerant circuit. Also, low line voltage or a brown out could make it difficult or impossible for the compressor to start.

It would be best not to run the unit until a technician looks at it, otherwise you risk trashing that compressor.

From what I saw on TV for out there and the brown outs It would pay to put a timedelay or or volt dropout on the unit there

Thanks for the replies. I'm leaning toward something electrical as this only has happened when both a/c's were run simultaneously, creating a massive power draw. If it happens again I'm going to use a voltmeter and check if the compressor is getting 240 volts. Thanks

Are these units on separate circuits? They should be, but you never know. A voltage check is in order. Let us know what you find.

Yes Jim, two separate lines & breakers. I'll let you know what I find. Mac