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HDGENE
HDGENE, ASE Master Tech
Category: Chevy
Satisfied Customers: 5431
Experience:  25 years Auto experience, Ford, GM, Chrysler, Asian & European
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I have a 2003 Silverado z71. My Ac is only blowing out the

Customer Question

I have a 2003 Silverado z71. My Ac is only blowing out the defrost. Took it too mechanic shop and they changed the actuator on the drivers side. That didn't work. They told me it was defiantly the Ac control head (the actual Ac controls on the dash). I just replaced that and it's still only blowing out of defrost. What else could it be?
Submitted: 11 months ago.
Category: Chevy
Expert:  Gary replied 11 months ago.

which actuator did they change ? under the heater box or on the side of the heater box near the gas pedal area ?

# ***** in this picture ? or was it under on the bottom of the heater box ?

Expert:  Gary replied 11 months ago.

picture

Customer: replied 11 months ago.
Drivers side near gas pedal
Customer: replied 11 months ago.
I know it was the drivers side becauseI actually pulled the actuator myself but the whole wheel came with it. Got agrivated and took it to my mechanic.
Expert:  HDGENE replied 11 months ago.

Hello, they replaced the mode door actuator. A diagnostic check for codes of the both HVAC and Body Control module need to be done t see if there is communication with the new HVAC module and if any codes are stored to indicate an issue with one of the blend door motors or their circuits.

Customer: replied 11 months ago.
Is there any diagnostics I can do at home? Testing pins on actuator harness? I know I can take it back to the mechanic but it seems like I get burned every time. He said that his scan tool said there was no communication with the actuator and that's why he said it had to be the Ac control unit. After changing the unit and nothing's changed I'm wondering if he knows what he is doing. I also noticed that my old actuator is in there. I called the mechanic and he said when the new one didn't fix it he put back in the old one. Is there anyway I can confirm with a volt meter on weather or not the actuator is getting the correct signal?
Expert:  HDGENE replied 11 months ago.

Is it a manual ac control panel or automatic?

Customer: replied 11 months ago.
Not sure. It has the digital screen and you can control different temps for drivers and passenger side. I'm guessing that dual climate control?
Expert:  HDGENE replied 11 months ago.

Ok it is an automatic system. Here is some basic information:

Air Distribution
The HVAC control module controls the distribution of air by the use of a mode actuator. The modes that may be selected are:

  • Defrost
  • Defog
  • Panel
  • BI-Level
  • Floor

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door, the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

Mode Actuator
The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control module sends signals to the mode door actuator through the mode door control circuit. Zero volts drives the actuator in one direction while 5 volts moves the actuator in the opposite direction. When the actuator receives 2.5 volts , the actuator rotation stops. A 5-volt reference signal is sent out over the 5-voltreference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control module's software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position.

Front Defrost
When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3°C (38°F) . The blower motor will be activated, regardless of the coolant temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.

Recirculation Operation
The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.

You can unbolt the actuator that was replaced and reinstalled and cycle the control panel through the different modes and see if it moves, Also manually move the door on the ac box to make sure a door isnt binding up and moves freely. It should move and change airflow.

All the testing requires the use of a scan tool since it is electronically controlled

Customer: replied 11 months ago.
I can't take a volt meter and test the pins at the harness looking for the 2.5 and 5 volts listed above?
Expert:  HDGENE replied 11 months ago.

Thats the only thing you can do.

Expert:  HDGENE replied 11 months ago.

This is the circuit schematic.

Customer: replied 11 months ago.
If I take it back I'm sure he will tell me that his scan tool is telling him that there is no communication between control unit and actuator just as he told me before. Since the control unit and actuator has supposedly been changed what else is there? All the wires I could inspect look good. Does the bcm play a part in any of this?
Expert:  HDGENE replied 11 months ago.

Yes it can as I mentioned you need to check for codes in the BCM and the HVAC modules. A continuity test of the wiring from the HVAC module to the door mode actuator will tell if there is an open circuit.

Expert:  HDGENE replied 11 months ago.

The BCM is more for compressor clutch operation. Just something they want to have tested in the diagnostic proceedure

Expert:  HDGENE replied 11 months ago.

Also there is a relearn proceedure for a new HVAC module:

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.

  1. Place the ignition switch to the OFF position.
  2. Disconnect the scan tool.
  3. Install the HVAC control module.
  4. Re-connect all previously disconnected components.
  5. Start the vehicle.
  6. Wait 40 seconds for the HVAC control module to re-calibrate.
  7. 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.

Preferred Method (W/ Scan Tool)

  1. Clear all DTCs
  2. Place the ignition switch in the OFF position.
  3. Install the motor assembly.
  4. Re-connect all previously disconnected components.
  5. Start the vehicle.
  6. With the scan tool, initiate the Motor Re-calibration feature of the HVAC module Special Functions menu.
  7. 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.

Alternate Method (W/O Scan Tool)

  1. Clear all DTCs
  2. Place the ignition switch to the OFF position.
  3. Disconnect the scan tool.
  4. Install the motor assembly.
  5. Re-connect all previously disconnected components.
  6. Remove the HVAC/ECAS fuse for a minimum of 10 seconds .
  7. Re-install the HVAC/ECAS fuse.
  8. Start the vehicle.
  9. Wait 40 seconds for the HVAC control module to re-calibrate.
  10. Verify that no DTCs have set as current DTCs.
Customer: replied 11 months ago.
All the pins have voltage at one time or another switching through the different settings. I know this does not diagnose it properly but with all pins having voltage and the actuator not moving at all just makes me want to replace the actuator myself. I pulled it back off and of course the plastic wheel came with it again. Do you have any diagram showing how this wheel goes back on? I see 2 slots a tit can go in. Just trying to figure out what goes were?
Expert:  HDGENE replied 11 months ago.

There are two differet types of systems, im thinking you are talking about this.

You should also perform the calibration as I mentioned before when replacing the acutator

Expert:  HDGENE replied 11 months ago.

Do you need more help with this concern?

Customer: replied 11 months ago.
please. I replaced the actuator myself and now it only blows out of the front vents. I checked continuity between all the wires going out of the Ac control module to the actuator and there all good. I'm starting to wonder about the wires coming into the control module. Do you have a wiring diagram for the Ac control module?
Expert:  HDGENE replied 11 months ago.

All I have is the circuit, anything internal to the module is not serviceable

Expert:  HDGENE replied 11 months ago.

Hello, do you need more help with this concern?

Customer: replied 11 months ago.
I just don't know what else to try. I've replaced the Ac control module and the actuator twice and checked continuity between all the wires between the control unit and the actuator. All the mechanics scan tool is telling him is that there is no communication between the control head and the actuator. Does not make sense.
Customer: replied 11 months ago.
This truck is odd because it is a half ton gas engine but came factory with 2 batteries. I wouldn't think that would have anything to do with this?
Expert:  HDGENE replied 11 months ago.

Then that is what has to be gone after, either the control head is defective, the actuaotr is defective or there is a wiring issue between the ac control head and the actuator, long as you did the recalibration of the control head and actuator, a test for codes for the HVAC and BCM would tell more, if there is no communication it should set a code, depending on the code number would dictate what test to follow

Customer: replied 11 months ago.
I've replaced all that. Could a faulty bcm cause this?
Expert:  HDGENE replied 11 months ago.

You have to find out what code(s) are stored the code number. Once you have the code number, you can perform the appropriate test before you condemn a module

Expert:  HDGENE replied 11 months ago.

Do you need more help with this concern?

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