AC Issue

[eparra]

My rooftop AC only runs in high speed and works fine there. The low speed doesn't come on. I do hear a buzz from the unit. Any ideas on what to check? Thermostat, blower motor, capacitor????? Dometic 13500 BTU in 2003 Mnnie Winnie.

[GaryKD]

Hi eparra,
Is the fan speed controlled manually or automatically.

[eparra]

It has Auto and Fan Low/High settings on the thermostat. And it only works in the Fan High mode.

[GaryKD]

Hi eparra,
If you have a meter and are comfortable working with it consider exposing the wires behind the selection knob. See if you have power into the switch and power out of the switch to the low speed setting. If there is power in but no power out of the switch, the switch is to blame If you have power in and out of the switch, one needs to get the wiring diagram and trace the power until it is lost. At that point is the failing component.

[TXiceman]

Could be a bad switch or a bad motor.


Ken

[eparra]

I am an Electronic Tech by trade just don't know much about AC. I'll check with meter and see if switch is good. Does wire from High/Low switch go to a relay that passes the 110VAC to separate wires on the fan motor, one for low speed and one for high speed, or is there one wire to run motor and different AC levels are sent to it?
Thanks for the help.