My family went on a trip to see relatives in the country. When we came back the a/c had quit. The inside blower motor works, just the outside unit will not turn on. Everything is fairly new, except for the thermastat on the wall, which is one of those old round mercury like switches.

I took the cover off the outside unit to inspect the capacitors, and connections. Everything looked fine. Niether compressor nor fan will turn on by itself. I pushed on the dual pole contactor and the unit jumps to life and will cool the house, I just refuse to hold it all night .

What do I need to replace to make the unit turn on by itself?

Thanks, Andrew

labman

If the furnace blower is coming on, power is making it from the thermostat back to the furnace. You should have a pair of wires running from the Y and B or C terminals at the furnace out to the contactor. If they have 24 volts outside, the contactor is bad. If not, check the wires between it and the furnace.

zoom

Thanks for the help. Appearently there was only 24v + going to the contactor. I just took the - and screwed it to the unit housing, and it works fine now. I also went ahead and installed a new digital thermastat since the round one aggravates me...


Thanks for the help.

Andrew..