I replaced a regular thermostat with a Nest and having a problem in which the AC will turn on, but then immediately turn off (fan in the AC starts up but then turns off, you can also hear the switch click off). The blower fan keeps on for a bit but the thermostat starts counting down to when it will turn the AC back on. Once it counts down the system goes through the same cycle: AC turns on then off with the blower running for a bit. I initially installed the nest a couple weeks ago and when I tested it the AC was working fine. Tried it today and having this issue.
Old Thermostat
Nest
Unit Picture
@Brad3301 , I believe you have a 2-stage gas Furnace system here. You have a furnace control board that has a yellow jumper between Y1 and O. However, you have no O wire going to your outdoor unit. I am not sure why the jumper is there. The Brown wire from your thermostat is not wired to the Common as you have it installed on the Nest. The brown wire is wired to W2 which is 2nd Stage Heat. From what I can see from the picture of your Furnace Control Board your Blue wire is connected to Common. Your brown wire needs to be moved and placed in your Nest *OB connector and defined as 2nd Stage Heat, Gas, Forced Air. You need to locate the BLUE insulated conductor inside the brown thermostat cable and connect it to C.
Do me a favor, get me the manufacturer and model of the Furnace and the same for the outdoor unit. I would like to pull out the service manual and see if in the sequence of operation, there is any reason to jumper Y1 to O.
I hope this helps you solve your problem.
AC Cooling Wizard
