Fan not working on hi

[Blue85]

Another mod I've considered is to swap out the factory relay socket for a standard relay socket and then run a standard relay instead of the specialty one normally mounted on the evap box. If you have relays for radiator fans, fuel pump, etc, running one common type means you can carry 1 spare for all of them. Of course if you hack up the wiring and use crimp fittings to do this the overall reliability will go down, not up.

 

[Blue85]

Revisit: Shorting across the NC contacts does have a side effect. If the fan is in HI when you turn the HVAC to "off", the relay remains energized and the fan keeps blowing. To stop it, you have to to move the speed switch to another speed. This implies that the speed selector switch is not a simple 1P4T switch, but something with multiple taps connected at a time.

Don't know when I'll have a chance to look at it some more. I guess a diode could be wired into the relay instead of a wire. Will have to look at the effect of voltage drop and dissipation.

 

[dyeager535]

Not that it has any bearing on this, but just thought about the heavy duty heater option not using a relay. Apparently the same fan motors, but the fan itself is a bit smaller on the HD setups, I suppose it's not odd GM went cheap and didn't use a relay in those setups. I've burned out a fan switch on the "high" setting, now I know why. Of course, as always, how many years did it last?