Hvac Question

ss502gmc · July 28, 2009

I was wondering if anyone could tell me what the voltage range should be at the top blend door actuator 01 silverado 2500 that controls direction of the air flow to the different vents because im trying to determine if my actuator is bad or the controller. Also the issue im now having is the actuator works in one direction and then gets stuck in that one position and then starts making a clicking sound and jerking around. i also plugged in another actuator and it did the same thing so i was wondering if its the controller or something. Some guidance would be great as my truck is now in pieces and not drivable. Thanks in advance!!!!

bill190 · July 28, 2009

For 5-wire actuators...

Looks like about 5 volts to move the door and 2.5 volts to maintain the door position.

Then there is a 5 volt reference signal to a potentiometer inside the actuator which would give door position feedback information to the HVAC controller.

Try removing battery power, then reconnecting. Turn on ignition and wait for about a minute. This should get it to recalibrate the door actuators.

ss502gmc · July 28, 2009

For 5-wire actuators...

Looks like about 5 volts to move the door and 2.5 volts to maintain the door position.

Then there is a 5 volt reference signal to a potentiometer inside the actuator which would give door position feedback information to the HVAC controller.

Try removing battery power, then reconnecting. Turn on ignition and wait for about a minute. This should get it to recalibrate the door actuators.

Thanks for the info! Also is there a way to check the harness that goes to the actuator? Like check the ohms reading or something? If so what should it read? Thanks again!

bill190 · July 28, 2009

I think the best way to test the wiring would be to tap into all 5 wires at the actuator or if you can place your volt meter test leads in the wire side of the connector (with connector plugged into the actuator). Sometimes there is a bit if metal from the terminal inside the connector which you can reach with multimeter test leads or a paperclip.

Then test for voltage on each lead as the actuator is working going back and forth. First with one test lead to ground. Then next with one test lead to +12v.

Then compare these readings with another actuator which is the same.

This would be the best way because you are testing the circuit with a "load" on it. And the wires go back to a computer module - and testing for ohms would place a voltage on those wires and could damage the electronics in the computer.

Then just testing for voltage with the connector disconnected might show good, but with a poor connection and a load, that voltage could drop to 0!

Also if you shove a test lead into a connector, you can spread out the terminal and damage it. So not good to do that!

So best to test the circuit for voltage with it connected and operating. Then compare with another actuator.

Note that one of these wires would be a "position" sensor wire. And the voltage would increase/decrease as the actuator moves back and forth. This tells the computer where the actuator is.

Then if possible, do the same test at the computer end of the wiring. You would need a factory wiring diagram for this.

Also a GM dealer might be able to tell if an actuator if working with a Tech II scan tool?