When I turn on my central AC, the furnace fan starts up and runs for a second or two then shuts down. The diagnostic led on the controller indicates Normal - no heat call.
The outside compressor unit continues to run, without the furnace fan blowing.
I turned on the heat, and it works ok.
Does anyone have a suggestion on how to troubleshoot this further?
Thanks, SD.
My guess would be a bad starting capacitor on the motor. How old is it?
If the motor works fine for heating, its not the cap.
If you have a switch for the fan on your T-stat, set it to "on" and see if the motor comes on. Then adjust the T-stat so the A/C comes on, leaving the fan switch on. If the fan continues to run, there may be a problem with the wiring of the T-stat which prevents the fan from coming on in the "auto" setting.
... except that the two run at different speeds.
MOST direct drive blower motors don't have a start cap, only a run cap. Split phase motors don't have a run cap at all.
Fan relay could be bad, if it uses one. Call an A/C company.
- udarrell
The fan will run if the thermostat switches are: Fan-On+Cool/Heat - Off, Fan-Auto, Cool/Heat-Heat. As soon as I switch the Cool/Heat to Cool, no matter what the Fan setting is at, the Fan shuts down. If I turn the cool/heat Off, and have Fan-On, the fan won't come on until I switch the Cool/Heat to heat. I took the thermostat out of the picture. If I hook Red-Green - Fan comes on, If I hook Yellow-Green - Compressor comes on. As soon as I add Yellow to Red+Green the fan shuts off.
My final troubleshooting attempt...I moved the blower fan motor wires around to try and use a different fan speed for the cooling function. No help..it behaves the same on all speed positions. I'm thinking that its the circuit controller.
The other possibility is that the wiring on the circuit board is wrong. Check there.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.