Bunk A/C always on low???

Could be power supply isn't cutting it...maybe upgrade the source wire...less resistance.

 

Replace the SWITCH !!! I replace my fan motor and it did the same but after I replace the switch, IT WORK !!! I need blanket's now....

 

If it's anything like the front blower motor, there's a resistor block that works in conjunction with the fan switch. When they burn up, the fan only works on low on all settings. If it only works on the low setting and turns off on the other speeds, it's the switch.

 

Thats what i did, replace that block as well.

 

First thing I'd do is to swap the high speed fan relay and see if that works.

 

I had a Freightliner that did the opposite when the resistor went bad, had NO low speeds but would work on High, guess it depends on how they are wired.

 

What he said. You should also be able to pull the switch and remove the incoming and outgoing wires and hold them together and should run on high, confirming the bad switch.