The subject says it all. Could this be the ACC head unit, or is it always the blower regulator? What should be tested and how? Thanks.

__________________
NOW: 2017 C43 AMG, 2006 Wrangler Unlimited Rubicon, 1966 230SL, 1980 450SL (for sale!)
PAST: 2006 C230, 1997 E300D, 1994 E420, 1994 Neon Spt Cpe, 1984 300ZX, 1983 Celica GT, 1976 Electra Limited, 1984 Honda Nighthawk 650, 1979 Suzuki PE175, 1978 Suzuki DS100
www.mbca.org - www.sl113.org - www.ohio4x4.com

Pull down the regulator/blower assembly.

On the blower assembly there is a regulator module.

3 wires coming out from the vehicle harness.

Fat red and brown are the constant hot and ground.
Skinny yellow is the speed reference from the climate control unit.

Put a meter on the skinny yellow and ground and run the fan speed up and down. Be careful that motor has a ton of torque and that blower wheel eats fingertips.

If the voltage on that skinny yellow wire goes from approximately 1 to 6 volts as you go from min to max fan the CCU is ok.

Now check the voltage across the motor, it will go from about 2 to 12 volts as the speed setpoint is run up.

If those check out the motor is probably bad. If not its the regulator. However your motor is probably worn out if original and it would be good to replace it. I got mine from Pelican.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Awesome troubleshooting steps! Thanks. I’ll update the thread after I have time to do this.

__________________
NOW: 2017 C43 AMG, 2006 Wrangler Unlimited Rubicon, 1966 230SL, 1980 450SL (for sale!)
PAST: 2006 C230, 1997 E300D, 1994 E420, 1994 Neon Spt Cpe, 1984 300ZX, 1983 Celica GT, 1976 Electra Limited, 1984 Honda Nighthawk 650, 1979 Suzuki PE175, 1978 Suzuki DS100
www.mbca.org - www.sl113.org - www.ohio4x4.com

JayBob,

I've got everything apart, but I don't see how I'm going to do the multimeter test. The fat brown ground wire has an exposed connector I can access as a contact point, and I could remove insulation from the yellow wire to get a contact point, but I don't know how to hold the multimeter contacts on there and position the fan so it won't hit anything and still control the ACC unit. I'm not an electrician, so maybe I don't have the right tools? Should my multimeter have some kind of clamp ends instead of just posts?

OK, that was a stupid question. I guess I need something like this?

https://www.ebay.com/i/274001720607?chn=ps

https://www.autozone.com/miscellaneous-non-automotive/jumper-wire-test-leads/dorman-alligator-clip-test-lead/297077_0_0?spps.s=5040

Attached Thumbnails

 

__________________
NOW: 2017 C43 AMG, 2006 Wrangler Unlimited Rubicon, 1966 230SL, 1980 450SL (for sale!)
PAST: 2006 C230, 1997 E300D, 1994 E420, 1994 Neon Spt Cpe, 1984 300ZX, 1983 Celica GT, 1976 Electra Limited, 1984 Honda Nighthawk 650, 1979 Suzuki PE175, 1978 Suzuki DS100
www.mbca.org - www.sl113.org - www.ohio4x4.com

Look further upstream on the wiring harness, there should be a connector to the vehicle harness from the regulator. You should be able to back probe the connector there.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech