Blend and mode door actuators not working after replacement of both and replacement of HVAC control module

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#15884 Closed 1995 GMC Sierra K1500 public

I bought a 95 GMC K1500 last month and i noticed both the mode door and the blend door actuators had been removed and the doors were being operated manually by vice grips. I assumed the actuators were bad so I replaced them both and still they didn’t work. So I went and found a used HVAC control module and the actuators still don’t work. However a couple times I have tried to operate them after I connect them, the mode door actuator will move all the way to one side before it limits out and I can’t control it. I had a noticed a similar result from the blend door once too, but it limited out in the other direction without being able to control it. Other times they don’t move at all despite trying to control them from the control module. I don’t exactly know how to test the wiring to the actuators to see where my problem may be. I haven’t blown a fuse since I’ve been working on it. The fan control dial works perfectly, as does the AC button and the recirculation door actuator.


Can you provide the part numbers and brand of replacement actuators?

Was the used control panel out of the exact same type of vehicle?  It looks like the 1995 year model may be different from all other year models.

Are all of the links and levers present and properly installed for the mode actuator?

I found this test procedure for testing inputs to the mode actuator. Testing should be similar for the temperature door actuator with the exception of the color of the control wire. It should be light blue.

1. Locate the mode door motor, just above the gas pedal.
2. Test voltages at the mode door motor.
3. With the ignition on, there should be 12 volts between the Brown (+) to the Black (-) wires.
4. The white wire should have: 1 volt on defrost, 6 volts on heat and 12 volts on A/C.  Use either the black wire or known good chassis ground as ground test point.
7. If OK, remove the mode door actuator, check linkage when attempting to change modes manually.

I figured it out! That advice was great. I realized I had loose connections at the wiring harness at the back of the module for the actuators. Once I knew what voltage I was supposed to have I started wiggling wires and found the problem. Also the new actuators I ordered didn’t work, the one just quivered in place when I tried to move the mode door. The replacement actuators are SKP brand, SK604107. It said they were compatible on RockAuto. The original actuators were reinstalled and still work fine.


Glad to hear you were able to figure the issue out. I am always amazed at how much effort people will put into not fixing something. Instead people like us  will take our time to seek out good information, then use fairly simple test methods to diagnose and repair the problem. Hope you enjoy the comfort of your truck’s HVAC system for years to come.

Thx again

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