No air from defrost vents, A/C is fine

Tiny
MOLLLYPOP
  • MEMBER
  • 2001 CHEVROLET PRIZM
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
When I turn on the defrost, no air comes from the vents. The front air vents and leg vents work fine.
Tuesday, November 13th, 2018 AT 1:30 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,896 POSTS
Hi and thanks for using 2CarPros. Com.

What determines air flow direction is called a mode actuator door. The mode control determines the air flow to the desired air outlet. The mode control is mechanically connected by a cable to the mode door. The mode door position determines the air flow to the ventilation, bi-level, heat, heat/defrost, or defrost air outlets.

With that in mind, I suspect the cable needs readjusted or replaced. Here are the directions for adjusting the cable to the mode door. Picture 1 correlates with these directions.

_______________________

1. Remove the knee bolster.
2. Remove the mode control cable from the clip at the HVAC module assembly.
3. Set the mode dial to Defrost.
4. Hold the door lever fully forward (counter clockwise).
5. Install the cable to the clip.
6. Test the cable for smooth operation.
7. Test that the door opens fully in both directions.
8. Install the knee bolster.

_______________________

If you find the cable needs replaced, here are the directions for replacement. After replacement, you will need to follow the adjustment directions. Picture 2 correlates with these directions.

_______________________

MODE CONTROL CABLE REPLACEMENT
MODE CONTROL CABLE REPLACEMENT

REMOVAL PROCEDURE

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1. Remove the center console trim bezel. Refer to Trim Panel Replacement - IP Center in Instrument Panel, Gauges and Console.
2. Remove the knee bolster.

IMPORTANT: Note the routing of the cable to make installation easier.

3. Disconnect the mode control cable from the heater case.
4. Remove the two screws and the pull the heater control unit forward:
5. Disconnect the mode control cable from the heater control unit.
6. Remove the mode control cable from the vehicle.

INSTALLATION PROCEDURE
1. Position the mode control cable in the vehicle. Route the cable as previously noted.
2. Connect the mode control cable to the heater control unit.
3. Install the heater control unit to the Instrument Panel (IP). Secure with the two screws.
4. Connect the mode control cable to the heater case.
5. Adjust the mode control cable. Refer to Mode Control Cable Adjustment.
6. Install the knee bolster.
7. Install the center console trim bezel. Refer to Trim Panel Replacement - IP Center in Instrument Panel, Gauges and Console.
______________________________

Please let me know if this is helpful or if you have other questions.

Take care,
Joe
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Tuesday, November 13th, 2018 AT 6:36 PM

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