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Hey everyone, I just picked up a 1991 ZR1 and I am having an issue with the AC blower speed. I can adjust the temperature of the AC fine, all of the other buttons work, etc. This is the C68 Climate Control by the way. The one thing I cannot do is adjust the fan speed when I click the up and down buttons the numbers go from 1-10, but the blower speed does not change it seems to be stuck on high I believe. Any ideas or easy fixes I can attempt before really digging into this? Thanks!
It could be the blower motor resistor. My '89 had the same problem. Swapped out the resistor and it resumed normal function. It's located on top of the heater box and held in by 3 7mm bolts. There are video's floating around on how to test them to see if that is the problem. I have a parts car so it didn't bother with checking it. Hope this helps.
The module in the evaporator box is not a resistor network like the manual systems. It is a solid state device that gets 10 steps of input voltage from the programmer and then drives the blower motor up to 12 volts for full power.
Check the wires also to the module because a bad connection or burnt wire like a ground can make the fan run full speed with no control. If the connections are good and wiring OK then it probably the module.
So I swapped the blower control module from my other C4 and I know that works because I can control the fan speed on that car. I put the working one on the car that I cannot control the fan speed with and the issue is still present. I am still unable to control my fan speed. Do y'all think it could be the HVAC programmer under the dash? I am also having the issue where the AC is only blowing out of the defroster and floor vents.
Check fuse #1 in the fuse box in the passenger door.
Make sure pic "C" of the module connector is ground.
**Correction
Back probe pin "C2" of the module connector with a volt meter. Run the fan control from low to high and see if the voltage varies from a couple volts to 9 or 10 volts (can't remember exact voltages at this time).
One of these items is probably bad. That's the direction you go.
Last edited by pcolt94; 08-02-2022 at 10:53 PM.
Reason: Correction
Check fuse #1 in the fuse box in the passenger door.
Make sure pic "C" of the module connector is ground.
Back probe pin "A" of the module connector with a volt meter. Run the fan control from low to high and see if the voltage varies from a couple volts to 9 or 10 volts (can't remember exact voltages at this time).
One of these items is probably bad. That's the direction you go.
The fuse is good. I’ll he honest I have no clue how to test the “C” connector or the “A” one. Can you PM me a more in depth explanation?
I found the issue. There is a 5 amp fuse that is attached to the firewall behind the coolant reservoir. Just unbolt the reservoir and move it out of the way, you will NOT need to disconnect the coolant lines. Replaced the blown fuse and I now have control of my fan speed again. If anyone else is having this issue, I would give this solution a shot first since it is a 5 minute job and was 5 bucks to fix it. I will attach some pictures of where that fuse is located.
I found the issue. There is a 5 amp fuse that is attached to the firewall behind the coolant reservoir. Just unbolt the reservoir and move it out of the way, you will NOT need to disconnect the coolant lines. Replaced the blown fuse and I now have control of my fan speed again. If anyone else is having this issue, I would give this solution a shot first since it is a 5 minute job and was 5 bucks to fix it. I will attach some pictures of where that fuse is located.
just an fyi fellas, the 91 l98 base coupe with c68 has a fuse in the same spot.
Some additional information.
I know the 90 and 91 uses this fuse on the firewall. My 94 does not. I have the schematics to look at and I checked my own car. So sometime GM dropped this fuse in this location which is feedback to the programmer. The fuse was moved to the fuse box inside the car #1 So either 92 or 93 the fuse was moved from under the hood to inside the car. I'm guessing the change was done in 92. So this repair may not reflect to your car.
08-01-2022, 12:15 AM
C68 Cannot control AC Fan Speed
