My AC/Heater only blows on defrost?

Tiny
THOMHOHN
  • MEMBER
  • 2003 GMC SIERRA
  • 209,426 MILES
I have a 2003 GMC Sierra 5.3L V8 1500 4X4
It only blows air on the Defroster, Not on the front vents or the floor?
I have already replaced the dual climate control panel. (Below stereo)
I have already replaced the Door Actuator motor.
No change?
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have the same problem?
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No
Sunday, October 30th, 2011 AT 2:01 AM

3 Replies

Tiny
MERLIN2021
  • EXPERT
Usually its due to a vacuum leak in the black supply line or the vacuum reservoir is cracked.
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Sunday, October 30th, 2011 AT 4:27 AM
Tiny
THOMHOHN
  • MEMBER
Where is the vacuum reservoir located?
What does it look like?
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Sunday, October 30th, 2011 AT 4:45 AM
Tiny
MERLIN2021
  • EXPERT
Upon further investigation, you say you have auto temp control? This is a totally electronic system, so the control module is behind the center of the dash. I recommend a scan with a tool that can read the B, and U codes from the computer. This will pinpoint the problem B4 part replacement. Also recalibrate the actuators like this.
RE-CALIBRATING ACTUATORS
1. 2. 3. 4. 5. 6. 7.
Preferred Method (w/Scan Tool)
1. 2. 3. 4. 5. 6.
7.
Alternate Method (w/o Scan Tool)
1.
Clear all DTCs

IMPORTANT:Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.
Place the ignition switch to the OFF position. Disconnect the scan tool. Install the HVAC control module. Re-connect all previously disconnected components. Start the vehicle. Wait 40 seconds for the HVAC control module to re-calibrate. Verify that no DTCs have set as current DTCs.
When replacing the motor assembly it will be necessary to allow the HVAC control module to perform a re-calibration process. When installing the motor assembly be sure to perform one of the following:
IMPORTANT:Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.
Clear all DTCs Place the ignition switch in the OFF position. Install the motor assembly. Re-connect all previously disconnected components. Start the vehicle. With the scan tool, initiate the Motor Re-calibration feature of the HVAC module Special Functions menu. Verify that no DTCs have set as current DTCs.
IMPORTANT:Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.

When replacing the HVAC control module it will be necessary to allow the HVAC control module to perform a re-calibration process. When installing the HVAC control module be sure to perform the following:
10/30/2011

2. 3. 4. 5. 6. 7. 8. 9. 10.
Removal Procedure
1.
2. 3.
4.

Installation Procedure
1. 2.
3.
4.
Place the ignition switch in the OFF position. Disconnect the scan tool. Install the motor assembly. Re-connect all previously disconnected components. Remove the HVAC/ECAS fuse for a minimum of 10 seconds. Re-install the HVAC/ECAS fuse. Start the vehicle. Wait 40 seconds for the HVAC control module to re-calibrate. Verify that no DTCs have set as current DTCs.
REPAIR INSTRUCTIONS
NOTE:
Tighten

HVAC CONTROL MODULE REPLACEMENT
Tighten the screws to 1.9 N.M (17 lb in).

Remove the instrument panel accessory trim plate. Refer to BEZEL REPLACEMENT-INSTRUMENT PANEL (I/P) CLUSTER. Remove the screws from the HVAC control module. Depress the control assembly retaining tabs and remove the HVAC control module from the instrument panel. Disconnect the electrical connectors from the HVAC control module.
Fig. 86: Removing HVAC Control Module From Instrument Panel Courtesy of GENERAL MOTORS CORP.
IMPORTANT:The Key should be in the off position when connecting the electrical connectors to ensure proper calibration.
Connect the electrical connectors to the HVAC control module. Install the HVAC control module into the instrument panel, ensuring that the HVAC control module retaining tabs lock into place.
Refer to FASTENER NOTICE.

Install the screws from the HVAC control module.
Install the instrument panel accessory trim plate. Refer to BEZEL REPLACEMENT-

5.
INSTRUMENT PANEL (I/P) CLUSTER.
If interrupted improper HVAC performance will result.
Start the vehicle and let run for one minute.
Fig. 87: Installing HVAC Control Module To Instrument Panel Courtesy of GENERAL MOTORS CORP.

IMPORTANT:Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating.
10/3
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Sunday, October 30th, 2011 AT 1:41 PM

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