vetteonbeach

getting frustrated trying to figure out how the electrical works on the a/c controls on my '77....hoping to get some help here...

I found this thread/schematic searching this site

https://www.corvetteforum.com/forums...er-blower.html

but the colors don't match up exactly and not 100% sure the 79 is the same as the 77.

The issue is the fan isn't acting correctly. with the main control in the off position and the fan switch in the lowest position (off), the fan motor is on very low speed, which I understand may be correct.

If you leave the main a/c switch in the off position, but move the fan control lever to the "1" position, the fan motor appears to go to the high speed. no change when moving to position 2, but when move to high it slows back down to the original slow speed. when going back to position 2, it stays in low speed, then goes to high speed in position 1, and back to low speed in the off position.

If you move the main a/c switch to max, the fan speed runs on high as I think it is supposed to do.

If you go to normal or any of the economy choices (vent,heater, defrost), the fan control acts the same as when off.

I have a brand new control module installed, originally thinking that was the issue without doing any troubleshooting. I also have a new blower resistor, which didn't solve anything, and what I think is a new high blow relay - the new one came with 5 prongs and my original only has 3, so not really sure what to do with that....

any help would be greatly appreciated!!

thanks,

Michael

bruiser

Here is a diagram from my 77 manual.
I'd check the switch first for voltage in the different positions.

vetteonbeach

thanks, I went back out and traced the wiring some more - I figured out for one that I was looking at the wrong thing for the high speed blower relay (there is another relay under the console that has a pink wire going to it with only three wires...doh)

my colors match up with your wiring diagram, so that helped me get my head around it a little better. Both the pink wire and the yellow wire have voltage coming out at the same time in every position, indicating my new control module is bad out of the box....

thanks,

Michael

vetteonbeach

bruiser,
thanks again for the wiring diagram. I took apart the new switch and found an assembly defect causing the pink and yellow terminals to be shorted to each other. Looking at your wiring diagram, this would cause voltage to backfeed through the main control switch from the fan speed resistor (since it has 12v on it all the time) which would cause the high speed blower relay to be pulled in when the fan control switch was in position 1 or 2 -

hopefully this solves the issue... frustrating when new parts are bad!!

Michael