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Mode door actuator replacement

Tiny
DMECK
  • MEMBER
  • 1997 GMC SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 480,000 MILES
Air comes out on floor only. No mid or defrost. I replaced the actuator, but no change. I can see that it is trying to move, but does not move the vent doors. With the actuator off, the engine running, I can move the doors by hand to get floor, mid range and defrost, but not with the actuator in place. It seems like a fairly simple replacement, but I cannot figure out what I am doing wrong. Please help! Dwight
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Tuesday, October 30th, 2018 AT 12:03 PM

16 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

When you have the actuator off, does the motor turn when you command changes?

Was the door moving freely?

If the door moves freely, then the actuator should be the issue unless there is a voltage supply issue.

Roy
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Tuesday, October 30th, 2018 AT 12:14 PM
Tiny
DMECK
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First of all, this is the actuator directly above the gas pedal. That being said, yes, I can move the plastic part in the heater box that fits into the actuator motor with my fingers, changing the air direction from floor, to mid to defrost, but when the actuator is mounted, nothing happens, just heater air on my feet. I can see the actuator trying to move (barely) when the engine is running, but not enough to change the air flow. I have not tried to work the actuator un-mounted to see if it is moving, the directions
or warning in the box it came in said not to. Dwight
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Tuesday, October 30th, 2018 AT 1:32 PM
Tiny
DMECK
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What might a voltage supply issue be? Dwight
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Tuesday, October 30th, 2018 AT 1:35 PM
Tiny
ASEMASTER6371
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Okay, try it without it mounted and see if the motor moves.

Beyond that, you will need to do voltage checks to the actuator.

Roy
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Tuesday, October 30th, 2018 AT 1:36 PM
Tiny
DMECK
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Okay, I tried it and the motor moves maybe a 16th of an inch, back and forth as I move the selector from floor to mid to defrost. Barely at all.
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Tuesday, October 30th, 2018 AT 1:41 PM
Tiny
ASEMASTER6371
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Okay, sounds like you have a bad motor. I would get a new one. Even if it is new, it can be bad. Test the new one before installing.

Roy
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Tuesday, October 30th, 2018 AT 1:47 PM
Tiny
DMECK
  • MEMBER
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This is the second one I have tried. Both from the same parts store. Both with the same results.
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Tuesday, October 30th, 2018 AT 1:49 PM
Tiny
ASEMASTER6371
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Okay, check the voltage to the actuator. In the diagram, it identifies the power and ground. Verify they are present.

Roy
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Tuesday, October 30th, 2018 AT 1:59 PM
Tiny
DMECK
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I went back to the parts store, and I gave them all the information I have plus your input, in the end, they did refund the cost of the actuator back to me. They feel the part is good, but that there must be another issue ie: low voltage due to a bad relay, but we could not find a relay associated with this part. I will take it to a mechanic to have the voltage checked (we are getting out of my comfort zone now) as you have suggested. You have been very helpful and I thank you. Dwight
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Tuesday, October 30th, 2018 AT 2:40 PM
Tiny
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Okay, there is no relay. The voltage comes from the control head directly to the actuator as in the diagram I sent you.

Let me know how you make out.

Roy
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Tuesday, October 30th, 2018 AT 3:08 PM
Tiny
DMECK
  • MEMBER
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They have suggested that a bad or faulty switch, as in the control head, would account for the lack of voltage, even if it allowed a lessor amount through. Do you agree with this? Dwight
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Tuesday, October 30th, 2018 AT 3:23 PM
Tiny
ASEMASTER6371
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Who is they?
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Tuesday, October 30th, 2018 AT 3:46 PM
Tiny
DMECK
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The people at the parts store. Dwight
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Tuesday, October 30th, 2018 AT 4:07 PM
Tiny
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Okay, they are parts salesmen not technicians.

Those are the same people who told you about a relay that does not exist.

This is why the voltage at the actuator needs to be checked as I suggested way back. You need to verify power and ground to the actuator itself. If it is a voltage issue, yes, it may be the control head but it also may be a bad connection or wiring issue.

One step at a time. The voltage to the actuator is the next step.

Roy
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Tuesday, October 30th, 2018 AT 4:11 PM
Tiny
DMECK
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Thank you. That is what I will check next. Dwight
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Tuesday, October 30th, 2018 AT 4:28 PM
Tiny
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You are welcome.

Glad to help.

Roy
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Tuesday, October 30th, 2018 AT 4:31 PM

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