My AC won’t turn on and the thermostat is not functioning properly. Voltage reading at the thermostat fluctuates between 7-9 volts. No low voltage at the contacter. I am still getting 240 at the contacter and the override button allows everything to turn on. Any suggestions?

  • 1
    Have you put a shelf or picture up and damaged the wire?
    – Solar Mike
    Jun 3 '21 at 10:23
  • 2
    Is the control power supplied from a transformer in the AC condensing unit, or in the air handler/furnace? Jun 3 '21 at 11:29
  • The control power is coming from the air handler/furnace. No changes to anything near the wiring. Nothing hung up. Thank you
    – David
    Jun 3 '21 at 12:35
  • Are there batteries in the remote? I have seen cases where the batteries drew down the supply voltage from the transformer to the point the thermostat could not change states. Verify it’s not the thermostat dragging down the control voltage if there was no voltage I would look at the transformer or fuse on the control board. Since there is voltage it is the thermostat or contactor coil (you have the 240 and bypass works so it’s the contactor itself or the thermostat in most cases).
    – Ed Beal
    Jun 3 '21 at 16:55
  • Check voltage between R and every other terminal (W, G, Y at the least). Jun 3 '21 at 19:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.