I have a York Furnace in the Attic. Using a Honeywell rth7500d thermostat.
The system is set to heat
Kick the fan to ON and the AC kicks on.
Double checked the wires on the thermostat. Crawled up in the attic and look there to. Everything is wired as it should be.
So does the A/C run when the t-stat fan switch is set to on or when the blower kicks in for heating?
Make sure that Y (wire) is not making contact with G (wire)anywhere along the control circuit.
Other than that, there's no much you can do. Turn off the A/C disconnect to avoid compressor damage and call a technician.
there's a short somewhere between g - y, maybe the wire is pinched somewhere. check for continuity between g-y.
If Heat kicks on the AC does NOT kick on. I should clarify more.
Regardless if the system is in Heat or Cool and I just switch the Fan to ON instead of AUTO the AC will kick on. I just want to recurculate the air in the house without Heat or AC on.
that's because in heat mode with your thermostat only r-w are closed.
This is a simpel one..
you have a short between green and blue (G and Y)
This means both are toching.
Check at furnace to see what going on with green wire.
You might have a jumper on g amd y at furnace.
A simple temporary fix put green wire on y. you want have high speed fan but your ac will not come on untill you call for it.