Dash ac fan quit on high speed mode

[JC2]

While getting ready to take the coach in today for an oil change, I turned on the dash ac to max cool and high speed fan mode and noted everything was working ok. After going down the road about 1 mile, I went over a small bridge that has a slight bump to it and the fan quit on high speed. The fan will work on low and medium speed in ac and other modes but will not work on high. Any ideas on what might have cause this would be appreciated.

[bigskymt]

I believe your chassis still used a high blower relay for high speed fan only.
I'm not sure of it's location but following the wire harness back from the air box might help you locate it.
You might try a 'search' for the topic as there were several replies to the same problem recently.

[ga traveler]

Quote:

Originally Posted by JC2 While getting ready to take the coach in today for an oil change, I turned on the dash ac to max cool and high speed fan mode and noted everything was working ok. After going down the road about 1 mile, I went over a small bridge that has a slight bump to it and the fan quit on high speed. The fan will work on low and medium speed in ac and other modes but will not work on high. Any ideas on what might have cause this would be appreciated.

In fifteen years, I probably ran into this more than any other problem. For high speed only, you have a fuse under the hood for the blower. It is uaually a 20 amp. Yellow. If this fuse blows, everything will work but high speed.

[JC2]

Checked the wiring at rear of fan speed switch and it was connected ok. Checked for any applicable fuses under dash. Checked under the hood and found a lage flat 30a fuse for the blower and it was blown. When I put a new one in, it blew also. Can't keep replacing them at $3-4 dollars a pop. Now what?

[ga traveler]

Quote:

Originally Posted by JC2 Checked the wiring at rear of fan speed switch and it was connected ok. Checked for any applicable fuses under dash. Checked under the hood and found a lage flat 30a fuse for the blower and it was blown. When I put a new one in, it blew also. Can't keep replacing them at $3-4 dollars a pop. Now what?

Start by purchasing a circuit breaker to replace the fuse. the CB's are usually metal inclosed with blade fuse plugs. It will open and close without blowing. You of course still need to find the short.

[JC2]

Update. Found a wire from the switch to the blower motor had worn through the insulation from rubbing on metal under the dash and was causing the short. What a pita to locate.
My thanks to the (2) members out of 65000+ that responded with suggestions.