Dash Fan Switch - Issue?

Tim Terry

I've noticed in recent drives that my fan switch on the dash in behaving differently than before. When I pull into the garage after a drive, I generally turn off the A/C before stopping the engine. Sometimes rotating the switch to zero turns off the fan and compressor clicks off, but more often lately it does not. Yesterday, I cycled it a couple of times while the car was still running and could not find a position to stop the fan. In that condition, I turn the car off with the ignition key and the fan is still running. Then I cycle the switch through a few positions and back to zero, where the fan will finally stop.

Is this a switch problem?
With the ignition key off:
If relay A or B sticks closed, both fans run at low speed
If relay C sticks closed, one fan runs at high speed
If relay D sticks closed, neither fan runs

Relays A & B are interchangeable
Relays C & D are interchangeable

Any of the HVAC switches and sensors can fail and the fans will not run with the key off because they are powered by the ignition terminal at the key.

I hope this helps,

Tim Terry

Thanks for the info, but this is the heater blower fan inside the car. And it DOES run during the failure mode, even with the key off.

HVAC Fan Run-on with Key-off

Fuses 15 & 16 are always hot and supply relays J & K respectively.

If relay J fails closed, the HVAC fans will run at medium speed with key-off.
If relay K fails closed, the HVAC fans will run at high speed with key-off.

Tim Terry

Thanks! Pulled K last night and confirmed that it controls the fan on high speed. Cleaned off the terminals and pushed it back in - same failure mode. Planning to replace relay K.