Cannot control AC Fan speed

[402Z]

Hey everyone,

So I am having an issue where it seems like my AC blower fan is stuck on 10. All of the buttons on my head unit work. When I click the up and down buttons for the fan speed the numbers will go 1-10 but the fan speed will not change. I have swapped the blower control module with a working one and the issue still persists. Any ideas? Thanks.

[DRM500RUBYZR-1]

The FSM has a rather simple diagnostic chart for inability to control fan speed.
Likely suspects are control head, or a compromised wire, then some lesser possibilities.

You need to hook up a scanner first and see if from the scanner you can control the fan speed.
If you can it is a bad control head.
If not, wiring is the next thing to check.
Keep us posted.
:cheers:
Marty

[402Z]

The FSM has a rather simple diagnostic chart for inability to control fan speed.
Likely suspects are control head, or a compromised wire, then some lesser possibilities.

You need to hook up a scanner first and see if from the scanner you can control the fan speed.
If you can it is a bad control head.
If not, wiring is the next thing to check.
Keep us posted.
:cheers:
Marty

I have a tech 1 will that work? I?ve never used it before.

[402Z]

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.

[Matt B]

Very interesting, thanks!! So, what exactly is that fuse for?

[GOLDCYLON]

I assume it's the fuse to the rheostat blower control module but I will be honest I did not know that a fuse was there. I knew the blower control model was there. Nice find !!!!! :cheers:

[WARP TEN]

Great find! Who knew? That solution should be immortalized in Dynomite's Solutions section. --Bob

[CamP]

I don't know what GM was thinking when they installed that fuse in that location. It's completely hidden.

[DRM500RUBYZR-1]

The FSM has a rather simple diagnostic chart for inability to control fan speed.
Likely suspects are control head, or a compromised wire, then some lesser possibilities.

You need to hook up a scanner first and see if from the scanner you can control the fan speed.
If you can it is a bad control head.
If not, wiring is the next thing to check.
Keep us posted.
:cheers:
Marty

The FSM in section 8A page 66.6 is the brief diagnostic procedure specifically for inability to control fan speed.
Using the scan tool would have resulted in the continued inability to control the speed, which excuses the control head.
The very next thing is to check the continuity of the circuit.
In this case there would have been no continuity.
It then states " repair open in circuit 65 OR OPEN AC UNDERHOOD FUSE.

My point, particularly with the HVAC system is that the diagnostics found in the FSM are very good at guiding you to the problem quickly by following the
sequential instructions.
Glad you found the stealthy fuse. and fixed it.
Well done!

The FSM can be obtained on disc very inexpensively on the web.
Be prepared for the inevitable next issue.
You will pull out far less of your remaining hair, if you buy it and use it.
:cheers:
Marty

[Dynomite]

Great find! Who knew? That solution should be immortalized in Dynomite's Solutions section. --Bob

Now in "Solutions" 7th Post under "AIR CONDITONER & HEATER"

Cannot control AC Fan speed (http://www.zr1.net/forum/showpost.php?p=334543&postcount=4)

:handshak:

[WARP TEN]

Now in "Solutions" 7th Post under "AIR CONDITONER & HEATER"

Cannot control AC Fan speed (http://www.zr1.net/forum/showpost.php?p=334543&postcount=4)

:handshak:

Thanks to you once again, Dynomite! --Bob