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Air Conditioning - blower fan

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Old 09-11-2011, 10:51 AM
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C3-76
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Default Air Conditioning - blower fan

1976. For the past several months the air conditioner and blower has been working great. Got them working early in the spring. At that time I did not have any wiring problems. Just a very full evaporator housing, leaves and twigs. About a week ago the air conditioner and blower stopped working. Acts like there is no power to either. Operating the thub wheel in the console you can here the switch click but the compressor and the fan do not come on. None of the fan speeds work. I do not have an electrical diagram but have one requested from a CORVETTEFORUM memeber. I have checked all of the electrical connections that I can get to without disassembling the car. What would cause both the compressor and the blower to quit working? Any help would be greatly appreciated!!
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Old 09-11-2011, 11:36 AM
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I know they're different, but my 71 had the same symptoms. Mine was cause by either a loose connector or something was interfering with the thumb wheel switch under the console. I traced the voltages down to that area, and when I took the console off to troubleshoot, it just started working. From what I know, the thumb wheel switch is sort of the master for the blower and AC.
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Old 09-12-2011, 09:36 PM
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Thanks! I was thinking that but did not have a wiring diagram to prove my theory. I will chase that switch down one afternoon this week. Hope its that easy!
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Old 09-13-2011, 12:02 AM
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There are leaf switches in front of the thumb wheel which are sorta pita to get at. There are also a few plug in connectors that attach to the bottom of the wheel assembly. If one pops off it'll leave your HVAC system dead.

If you take the holding screw out of the rubber circular piece that has 5 million vacuum hoses attached to it, you can pull them out in one piece and have enough room to flip the thumb wheel assembly over.
Be careful not to break the strings or knock one of the little idler pulleys off...it will find its way to another dimension.

Had mine apart last week to fix the dial indicator and it's a cheesy setup.
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Old 09-13-2011, 05:57 PM
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Thanks. I had that apart earlier in the spring to put the moment arm on the thumb wheel. Really dont want to go back in there but I guess I will. Does anyone have part number for the switch? Looking on-line I find two different switches.
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Old 09-13-2011, 08:10 PM
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I pulled the console plate off and pulled the thumb wheel mechanism out. Took the two switchs off of the side of the thumb wheel mechanism. Each switch ohms out as good. I am going to assume I am looking for 12VDC at the wires. I have not been able to find any voltage. Does anyone know where the power feed is for the thumb wheel mechanism switches?

I checked for voltage at both switches with the ignition switch in the on position, radio playing.
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Old 09-13-2011, 09:30 PM
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On my 71 wiring diagram it looks like a brown wire to switch 1 (the master?). And a tan wire from the anti diesel relay via the blocking relay to switch 2.

The brown comes from the fuse block and the tan comes from the horn relay via the 12G orange wire.
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Old 09-13-2011, 10:14 PM
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Do you know where the air conditioner/blower fuse is located on a 76? I believe there is a 25 amp fuse in line somewhere that my be the problem.
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Old 09-14-2011, 12:15 AM
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Originally Posted by C3-76 View Post
Do you know where the air conditioner/blower fuse is located on a 76? I believe there is a 25 amp fuse in line somewhere that my be the problem.

My 75 has a white inline fuse holder near the high speed blower relay in the engine compartment (over evaporator housing). I can't remember if that kills the whole system but it's worth checking.
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Old 09-14-2011, 01:39 AM
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My blower fuse is inline on an orange wire over by the windscreen washer bottle.
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Old 09-14-2011, 07:28 AM
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Visibly checked the fuse by the blower relay. Fuse looks good. I will get the mulitmeter out this afternoon and see if the fuse is hot. Still not sure if the fuse by the blower relay is the fuse that feeds the whole system.
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Old 09-14-2011, 09:45 AM
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Originally Posted by C3-76 View Post
Visibly checked the fuse by the blower relay. Fuse looks good. I will get the mulitmeter out this afternoon and see if the fuse is hot. Still not sure if the fuse by the blower relay is the fuse that feeds the whole system.
I think that's only the blower high speed feed. I believe the remaining speeds and AC come from the fuse block.

What I did to test the blower was verify 12v on the orange feed up to the blower high speed relay. And then jumper that 12v (any 12v would do) to the input side of the blower speed resistor. This tested the different blower resistor circuits that control the speeds and the blower itself.

Last edited by C6DuffMan; 09-14-2011 at 09:50 AM.
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Old 09-14-2011, 04:44 PM
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This is the Heater - AC Schematic for the 1976.

I'll check back later tonight and give you some diagnostic tips on how to figure your problem. (I'm a bit short on time right now).


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Old 09-14-2011, 07:07 PM
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As promised... Here is where I would start.

Before you tear the dash apart: Check the orange wire at the hi-blower relay. This relay is mounted on the evaporator core housing.



If there is not any power there and as mentioned above. check the thirty amp fuse on the passenger side of the car. You'll find this fuse holder right beside the inner fender.

If you have power on the orange wire, then check the motor ground on the motor. Check the terminal and make sure it is clean. Verify that the ground is a good ground with a test light hooked to a power wire using the blower ground as the circuit ground.

Inline on the power wire to the motor is a capacitor. (shown below and on all cars with a radio). Make sure the jumper connection is good and if you suspect it is bad unplug it and plug the motor up direct without it.



Next.. If you have power and ground go to the resistor mounted on evaporator housing. (shown below) This is your lower speed resistor. The wires on this resistor yellow, Blue and Green are split off from the blower switch in the dash. When the blower switch in the heater control is in any speed other than Hi... you'll have power on one of these wires. The wires connect to the resistor in different stages to increase or decrease the amount of resistance and voltage to the blower motor.



If you do not have power on any of these wires then it is time to go in the dash. The Master switch (shown below) is located on the side of the heater control is what cuts power to all the wires on the blower switch. You see in the schematic the brown power wire going this switch and then the power goes out to the blower switch on the tan wire and to the compressor switch on the green wires.



See if you have power on the brown wire at the master switch.

Also.. verify the ground 150 at the relay.

Hope this helps and please post again your results.

Willcox Inc.

Last edited by Willcox Corvette; 09-14-2011 at 07:09 PM.
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Old 09-14-2011, 09:45 PM
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Thanks for the information. No time today to work on the vette. I will check for power at the blower relay tomorrow and post my results.
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Old 09-15-2011, 03:29 PM
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The schematic above pretty much lays it out but if you do have questions just post again or email me at [email protected] om
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Old 09-17-2011, 04:05 PM
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Thanks for the information. WILLCOX-the colored schematic you provided was very valuable. Found a short that was blowing the fuse.
THANKS!!!
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Old 09-17-2011, 10:59 PM
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Sweet.. Love it when a plan works out... have a great weekend.
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Old 02-16-2014, 08:27 PM
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Default Blower motor problem

Hope the guys at Wilcox can sort this one out.
As mentioned in other threads I have been searching,testing,looking everywhere because I couldn't get my blower to work.
Now for the latest. Couldn't understand why the black leads (twin) going to the regulator and the one going to the blower motor were both good "earths" however! When ignition is turned to on these "ground" wires become live. So I think I have found the cause ( but not the fix solution)

I accidentally left the ignition switch on overnight and as the battery was running down and got weaker the fans started up an flattened the battery even faster. So, in the morning with a dead battery I hooked up an external power pack to give it a very weak charge. Well! Then I tested the blower motor and it worked good in all speeds even with the "ground" wire to the regulator not even attached to anywhere, BUT, it did start to get warm as the car got more charge into the battery until when the battery is fully charged, the "ground" wires become live and the blower won' t work anymore until the battery gets weak again.
So, WHAT am I missing.
Sorry for such a long post but I am going bald pulling my hair out over this problem
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Old 02-16-2014, 09:16 PM
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Check at the starter and see if there is a black ground wire hooked up mistakenly with the large battery cable. The black wire is the ground for the blower motor and wiper motor and should be hooked to a bell housing bolt, not the starter lug.
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