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Super Mechanic
Super Mechanic, Master technician
Category: Chevy
Satisfied Customers: 16825
Experience:  29 yrs. exp., ASE master, cert. in G.M. electrical, a/c, susspension, brakes, electronic steering
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2008 chevrolet impala: the fresh air door actuator..clicking..controls

Customer Question

I have a 2008 chevrolet impala and the fresh air door actuator started clicking. I started to install a new one and turned on the key so the motor could set its self and it just kept turning. What controls the start and stop times for this motor? it appears to be overdriving
Submitted: 4 years ago.
Category: Chevy
Expert:  Super Mechanic replied 4 years ago.

Hello and welcome to Just, Super mechanic here. Please DON’T hit accept until you are completely satisfied with the answer. If you need any more on it just let me know. About your vehicle.

2008 Chevrolet Impala

Mode/Recirculation Actuator

The mode/recirculation actuator is a 2 wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.

The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across 2 commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.

Reset Procedure

Actuator Recalibration

Calibration Procedure

Use the following steps to perform the calibration update:

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Select HVAC Control Module
  4. Select Special Functions
  5. Select recalibrate All Motors
  6. Select ON, wait 60 seconds.

Customer: replied 4 years ago.

is there any type of scan tool you recomend? so after installing a motor, you need to recalibrate the system? what are the possibilities that the hvac control module is faulty?

Expert:  Super Mechanic replied 4 years ago.
I wouldn't think the control mod is the problem in this case, (although it is always possible with any electronic device that any part of the system could be bad)

They most times will calibrate on their own. They say not so plug them in before they are installed in the vehicle but it happens, (as you see)

The scan tool that we use at the GM dealerships is a Tech2 and you wouldn't save alot of money to buy one, (for around $5000 or so) and not really sure on the Snap-on ones and their capabilities.

I would put the actuator in and see how it does. Leaving the key on for abour a minute to allow it some time to find the stopping points.
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Customer: replied 4 years ago.

Well, I found out that it doesnt matter if you install a new motor and then connect it. The first motor broke the gears because of the overdrive. So I purchased a new motor and it did the same thing. I'm going to say its the control module.

Expert:  Super Mechanic replied 4 years ago.
That is always possible, the control module controls it according to a feedback signal the it gets from it. Like any other type of computer it may not be processing correctly.