A/C fan won't run on high

dougrainer wrote:
The odds are the hi speed fan wire is off the Roof AC control board if the hum is the compressor and not the fan motor. Open the roof AC filter cover and you will see the tstat wires to the control board, just look and see if one spade terminal is not connected. Doug

Bingo Doug! Took off the filter cover wiggled the high fan wire and boom, fan came on. Didn't spend enough time to see if it's the crimp on the spade connector or the connector itself. That'll have to wait till the weekend.

Thanks all for your advice.

DavinD wrote:

Old-Biscuit wrote:
T-stat is bad

fun times...I've seen other threads with digital T-stat replacements. Another project in my future.

Coleman Mach to Hunter Digital Thermostat swap. Simple...$25/Wally World
LINK

If you are positive it is the fan motor humming and not the compressor, go on top and gently touch the fan motor case. After 5 minutes of humming a defective hi fan speed winding will cause the case to be hot enough to burn you. That means the fan motor is bad. A defective tstat will not cause a fan motor to hum and not run. The odds are the hi speed fan wire is off the Roof AC control board if the hum is the compressor and not the fan motor. It could also be AT the wall tstat but rare if it worked previously. Open the roof AC filter cover and you will see the tstat wires to the control board, just look and see if one spade terminal is not connected. Doug

Old-Biscuit wrote:
T-stat is bad

fun times...I've seen other threads with digital T-stat replacements. Another project in my future.

T-stat is bad

Yes,it has worked before. I'm guessing the hum is the compressor. The fan will not turn on high even when not set to auto. I have 2 switches.

Left switch set to cool, right switch set to auto-high -- no fan but I hear compressor
Left switch set to cool, right switch set to auto-low -- works fine
Left switch set to cool, right switch set to on-low -- works fine
Left switch set to cool, right switch set to on-high -- no fan but I hear compressor
Left switch set to fan, right switch set to auto-high -- nothing
Left switch set to fan, right switch set to auto-low -- nothing
Left switch set to fan, right switch set to on-low -- nothing
Left switch set to fan, right swirch set to on-high -- nothing

Thermostat is Coleman mach

Has it ever worked before?

Try running the fan without the A/C compressor turned on. RU confusing fan noise with compressor noise?