71' fan speed switch on hi.

[walkman]

Have a 71'. Fan speed won't come on in hi position of the 4 position switch. I was told it is a resistor in the back of the duct work. Has anybody had this problem and how do you change it. I have a new one. I have searched threads and found none on this problem.

 

[JohnZ]

If you don't have A/C, blower speed is fed from the blower switch and the heater resistor located on the inside heater case, with high speed bypassing the resistor. If you have A/C, the lower three speeds are fed from the blower resistor located on the underhood evaporator case, and the high speed is fed directly from the horn relay through a 10-ga. red wire with an in-line fuseholder to a relay on the underhood evaporator case. No high blower with A/C is usually a blown in-line fuse or a bad relay.

 

[walkman]

Ok, I have a/c. So should I look at the in line 25 amp fuse. where is the underhood evap. case.

 

[Chas]

Maybe its just mine, but i noticed when i put mine on high , it shuts off and when i shut it off it goes to high....it seems like the positions have "shifted" one whole notch , or something like that. Turn your engine off and really listen to it to be sure its off or on low...when my vette is running, i cant hear the blower motor to know if its running or not.
just a thought for ya...
Chas

 

[LVMYVT76]

It is under your hood , on the firewall on the passenger side just in front of the wiper area. It has a large plug on top. the resistor has 2 screws holding it in place, take them out and lift it out,if the resister wires are burnt off, then it is bad.

 

[walkman]

I'll correct myself, it's a 30 amp in-line fuse. It was popped, I'll change it today and see what happens.

 

[George Black]

JohnZ is 100% correct. If AC fan switch does not work on high, it is usually always the blown 30 amp in line fuse. Located on driver's side fender by horn relay. Red wire. Give us a report back if that fixes the problem.

 

[walkman]

JohnZ is 100% correct. If AC fan switch does not work on high, it is usually always the blown 30 amp in line fuse. Located on driver's side fender by horn relay. Red wire. Give us a report back if that fixes the problem.

Yes it was the fuse. I think the relay/resistor is on passenger side where the a/c tubes go into the firewall area. The two relays/resistors up near the wiper motor on the drivers side, I'm not sure what they do. Unless I traced the wire wrong.

 

[F4Gary]

When I put my AC fan switch to high, my ammeter pegs full right. Is that the switch or the resistor in the evap case?

 

[walkman]

When I put my AC fan switch to high, my ammeter pegs full right. Is that the switch or the resistor in the evap case?

I don't know, you would have to take a volt/ohm meter and isolate. You have a short somewhere, could be in the blower motor.