mystery -- AC keeps stop shutting during the day

This has been driving me crazy. I had AC tech going three times. Still, we don't know what's happening.

this house is used by tenants. They had claimed that the circuit breaker kept tripping off during the day. AC tech replaced the AC circuit breaker.

Yesterday, they said AC shut down but circuit breaker didn't trip. But they accidently flipped the air handler switch. When AC tech go there around 8:00pm, all he did was to flip the switch of air handler. But the fact AC stopped working during the day is a mystery.

My AC guy made three trips. He measured Freon. It's OK. When the AC is on, it cools pretty well.

I plan to replace the thermo-stat myself later.

But what else can it be? Early in spring, I had another AC tech doing tuning. He charged 1lb Freon. I wonder if it's because the system is over charged?

My current AC tech suggests to replace the entire 11 year old system. He doesn't have any other diagnostics suggestions because issue is not reproducible.

 

When the AC stops again next time, you need to go there to check the contactor
first, and then capacitor second...., there are only a few things can go worng, should not be that hard to figure it out. Your AC guy is no good, how does he know by replacing the whole system will fix the problem ?

 

Your ac guy doesnt sound like hes checking amp draw or mf on capacitor. Check both of those at any given time

 

When the air handler switch was "ACCIDENTALLY" switched off, you may have lost the control voltage which was restored when the a-c tech switched the air handler back on that evening. I don't suppose your tenants are behind on the rent, are they? I am not quite sure how anyone with half a brain would accidentally turn off the air handler switch in a-c weather without realizing they had disabled the a-c system.

 

Thanks for the replay.
I did ask the AC tech to check capacitor and amperage draw for compressor. I changed capacitor a year ago. It checked out OK based on him. He checked the amperage draw reaching 14. I checked the manual, 14 seems to be normal for 100F temp.

good point about contactor. he never mentioned or checked. I will search and find out how to change contactor though I changed capacitor many times.