Cannot control AC Fan speed - ZR-1 Net Registry Forums

402Z · 08-03-2022

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 · 08-03-2022

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.

Marty

402Z · 08-03-2022

Quote:

Originally Posted by 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.

Marty

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

402Z · 08-03-2022

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 · 08-04-2022

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

GOLDCYLON · 08-04-2022

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 !!!!!

WARP TEN · 08-04-2022

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

CamP · 08-04-2022

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

DRM500RUBYZR-1 · 08-04-2022

Quote:

Originally Posted by 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.

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.

Marty

Dynomite · 08-04-2022

Quote:

Originally Posted by WARP TEN

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

08-03-2022	#1
402Z Join Date: Sep 2021 Location: Florida Posts: 29	Cannot control AC Fan speed 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.

08-03-2022	#2
DRM500RUBYZR-1 Join Date: Sep 2008 Location: Mullica Hill, New Jersey Posts: 2,576	Re: Cannot control AC Fan speed 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. Marty

08-04-2022	#5
Matt B Join Date: Jan 2021 Location: Beautiful Bavaria Posts: 523	Re: Cannot control AC Fan speed Very interesting, thanks!! So, what exactly is that fuse for? __________________ ZR-1 #638/1991

08-04-2022	#6
GOLDCYLON Join Date: May 2007 Location: Peoria, AZ Posts: 9,154	Re: Cannot control AC Fan speed 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 !!!!! __________________ GOLDCYLON - 91 ZR-1 #2014 GOLDCYLON - 90 ZR-1 #2794, 4L60e (Formerly Schrade's) GOLDCYLON - 11 CTS-V Arizona State Director 91 WHITE/BLACK #2014. 380 P&P&PCed,Ported Heads, Jeal Long tubes, Corsa Exhaust/FIKSE FM-5s /LED TLs, LED Headlights, Front Wilwood 6 piston narrowlite calipers and rear Wilwood caliper street shop mod,CNCed Coolant Pipes,TPI Cvr,Filter cover,Stainless Bolts, DRM/DOM PROM /ZFDOC mod build #102,DRLs,BMAD with stainless Debris Screen,Coplan Air Blaster, Pioneer APP Radio 4,Brey-Krause HB,Sub Bar,Fire extinguisher seat mount,DRM Coilovers,LEDs everywhere,Compass mirror (orange),V1 DIC hidden display, Homelink sun visor, Carbon Fiber top x3 and APSIS Carbon Fiber interior, APSIS CF Steering Wheel/NAPA Leather, Banski trailing arms, Guldstrand front suspension,urethane bushings from Prothane (total suspension) ZFDoc drive shaft safety loop, raptor shift light (orange),AO engineering louver front plate, Console seat cushion, 96CE seats with black custom Sheepskins, ss billet catch can,Viper remote entry/alarm,Cragar Rear Louvers,LED side louver lights, Dewitts Radiator with SPAL fans and a Woods 160 T-Stat 90 RED/BLACK #2794. 4L60e Automatic Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless Headers, Corsa Exhaust, SAN Secondaries and Haibeck PROM, Exotic Muscle Coil overs, LED Interior Lights, LED Tail Lights, LED Headlights, 94 Sport seats with black custom Sheepskins , Cragar rear louvers, GS Front calipers, Banski Trailing arms, APSIS Carbon Fiber steering wheel, Front and Rear Baer Eradispeeds, DRLs, Guldstrand front suspension,urethane bushings from Prothane (total suspension), Dewitt's Raditor with Dual SPAL fans and a Haibeck 170 T-Stat 11 RED/GREY CTS-V

08-04-2022	#7
WARP TEN Join Date: Apr 2007 Location: Lake Bluff, IL Posts: 2,072	Re: Cannot control AC Fan speed Great find! Who knew? That solution should be immortalized in Dynomite's Solutions section. --Bob __________________ 2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough"

08-04-2022	#8
CamP Join Date: Jun 2012 Location: fort worth Posts: 183	Re: Cannot control AC Fan speed I don't know what GM was thinking when they installed that fuse in that location. It's completely hidden.