Figuring out my Heater/Ac controls 75

[scotty17509]

So ever since i got my 75 the fan has been stuck on. Today I took the control switch out. While the switch was unpluged, i turned on the key and its still on. I am assuming that the top sliding vent controller is what should turn it completely off.

Anybody have some sugestions?

[GMC Guy]

my 79 was the same way, the fan was always on for some reason. couldn't figure it out, but i did away with all that ac crap anyway, so i never looked too far into it.

[asphaltburner]

Yo! Chevy designed the fan to come on at low speed when the key is turned on. The switch allows the use of medium and high speed. I routed a wire back from the positive the supplies the fan to a toggle, and I can now turn off the fan entirely. Slide controls only open and close vents.
Anybody know of a different way to accomplish this, or have better ideas?
Todd.

[wydomkr]

Originally Posted by asphaltburner

Yo! Chevy designed the fan to come on at low speed when the key is turned on. The switch allows the use of medium and high speed.

That has always bothered me, there really is no off...

[Pyrotechnic]

I think it's a safety deal to keep a constant flow of fresh air coming into the cab.

[83burban]

Doesn't the top lever (the one that switches between ac modes and heater) turn it off. That's the way it is in my suburban (all the way left turns the whole system off - including the fan)

[asphaltburner]

Yo! Not with my ol' '73 3/4 ton 4x4 Custom, '78 3/4 ton 4x4 Scottsdale, or the '81 1/2 ton 4x4 Scottsdale that I sold. But that's all I can attest to. Others could CERTAINLY be different, and I don't know if the controls are all the same. Also NONE of mine had A/C! Perhaps that's the difference,...A/C and heater only controls.
Todd.

[GMC Guy]

mine had a/c and it never shut off, but that's just mine

[scotty17509]

Hmm so does anybody know for certain if the 75 is SUPOSED to stay on? Maybe on later models they can shut off. Or maybe its a common problem with these.

[asphaltburner]

Yo! I know that the "heater only" fan comes on at low speed when the key is turned to the ON position,...three trucks outta three and I've heard this before from others. I thought it was a standard for ALL of Chevys' trucks, but A/C controls may work differently,...anyone know?
Built my '76 Camaro in 2002 (and immediately rewired it after completing removal of the remaining A/C components) but it seems that I had to unplug the fan at the resistor assembly to keep that fan from running when the key was turned on. Too long ago to know for sure.
Todd.

[powerdriver 1958]

Blower motor running when the switch is on, is normal for your truck.

[3r!c84]

when mine is off the fan dont come on?

[scotty17509]

Alright now i have another question. When i flip the vent to AC, it turns the fan up to high, and the fan switch has no effect.

[asphaltburner]

Yo! Yes!
I recall my Camaro doing the very same kind of "weird", pre "programmed" A/C things. I'm pretty sure it is designed to do just that for normal function of the air conditioning. I'll try to remember to look in my shop manual to see if I can find the explaination as to WHY it does that. I think the vent closes to outside air and cranks up the fan for max output to flood the car with cool air.
I DO believe you are experiencing normal function. Even with my Camaro rewired for heater only, I think mine still does this, but I only use the defrost, vent, and off positions.
Todd.

[scotty17509]

Originally Posted by asphaltburner

Yo! Yes!
I recall my Camaro doing the very same kind of "weird", pre "programmed" A/C things. I'm pretty sure it is designed to do just that for normal function of the air conditioning. I'll try to remember to look in my shop manual to see if I can find the explaination as to WHY it does that. I think the vent closes to outside air and cranks up the fan for max output to flood the car with cool air.
I DO believe you are experiencing normal function. Even with my Camaro rewired for heater only, I think mine still does this, but I only use the defrost, vent, and off positions.
Todd.

That would be great if you could find that out. I have my truck apart and dont want to put it back together if its not right.

[jwilson645]

Originally Posted by scotty17509

Alright now i have another question. When i flip the vent to AC, it turns the fan up to high, and the fan switch has no effect.

Sorry to bring up an old topic but my 77 does the exact same thing and I didn't see an answer in this thread.


The fan switch does nothing, there is a constant light flow of air from the vents until you switch it to a/c (max) and it blows hard. However, it only comes from the dash vents, no floor or defrost.