Front AC doesn't work back does

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Matthew Jeschke

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I am curious how to go about tr9ubleshooting this. My front AC blows ambient air... while the back works perfectly.

Video of what it is doing,


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Wes
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blend door actuator in the front is probably stuck or bad, has nothing to do with the a/c pump the a/c pump runs the entire system and is working.

you can check the actuator for operation at the point in the following video when pulls it out, you can then plug the power connector back in, turn the key to run and then turn the hvac hot/cold on the dash controller and see if the actuator rotates or not it should move all the way from mark to the next mark (hot to cold or vice versa)


 
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Matthew Jeschke

Matthew Jeschke

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Weird, I just replaced blend door actuactor. I get hot if I turn to hot.

I am curious is there a calibration for the blend door actuactor? Maybe this is the problem?

Also I was blowing compressor relays, then the system wouldnt work at all for a while so I replaced the dash hvac control and it seemed to start workong again

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Wes
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Weird, I just replaced blend door actuactor. I get hot if I turn to hot.

I am curious is there a calibration for the blend door actuactor? Maybe this is the problem?

Also I was blowing compressor relays, then the system wouldnt work at all for a while so I replaced the dash hvac control and it seemed to start workong again

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yes there is a calibration procedure, @swathdiver may know the procedure I do not off hand, if the procedure does not correct the problem I would check the blend door/actuator visually, sometimes the door it's self can break but I don't think it is very common on these trucks.
 

swathdiver

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yes there is a calibration procedure, @swathdiver may know the procedure I do not off hand, if the procedure does not correct the problem I would check the blend door/actuator visually, sometimes the door it's self can break but I don't think it is very common on these trucks.

From the GMT900 shop manual (not sure yours Matt is the same):

Actuator Recalibration

When replacing the HVAC control module it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC control module be sure to perform the following:

Important: Do not adjust any controls on the HVAC control module while the HVAC control module is self-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. Connect all previously disconnected components.
  5. Start the vehicle.
  6. Wait 40 seconds for the HVAC control module to self-calibrate.
  7. Verify that no DTCs have set as current DTCs.
When replacing the HVAC actuator it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC actuator 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 self-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 HVAC actuator.
  4. Connect all previously disconnected components.
  5. Start the vehicle.
  6. With the scan tool, initiate the Motor Re-calibration feature of the Heating and Air Conditioning 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 self-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. Install the HVAC actuator.
  4. Connect all previously disconnected components.
  5. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
  6. Install the HVAC/ECAS fuse.
  7. Start the vehicle.
  8. Wait 40 seconds for the HVAC control module to self-calibrate.
  9. Verify that no DTCs have set as current DTCs.
 
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Matthew Jeschke

Matthew Jeschke

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Thanks :) I just tried that, I was surprised as I didn't hear the temperature valve actuator doing anything, or the vent selector actuator.

I tried it a few times. I pulled fuse and tried it with that method. Then I disconnected the battery and tried it that way. I had power disconnected for minimum 1 minute... Bender door and vent selectors both set to middle of dial. Then I put ignition to ON for 3 minutes w/o starting. Next I started the truck and let run for 3 minutes. All the while not touching the selectors dials.

Shouldn't I hear the actuators moving while it's calibrating?


I noticed I have another problem not sure if is unrelated - I had it when I bought the truck. The vent selector actuator tends to hang up from time to time, especially after selecting defrost. Originally I used silicon grease on the track it moves and that did the trick. I think it had hung up again... but was able to get it to move to different vents after playing with the control selector.
 
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Matthew Jeschke

Matthew Jeschke

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As of last weekend the rear air stopped cooling as well. I removed the blend door actuator and moved the door to cooling side to make sure that wasn't the issue.
  1. The AC compressor engages but cycles quicker than I would expect. Probably 10 sec on then off, for 10 sec then on.
  2. The high pressure lines are extremely hot, like 150+ F hot, along with the condenser coil.
  3. The low pressure line (for front evap - no idea how to locate low pressure for rear). Was nearly frozen at onset of problem. Now it stays at ambient temperature.
I'm worried I have an obstruction in the system. Truck is my project vehicle. I got it with 220,000 miles, no idea as to service history of any kind.

Youtube video of current troubleshooting:


Photo is where the temperature difference is. I'm thinking was problematic before as I see a mark from a green mark leading me to believe a replacement part was purchased at a salvage yard.

I am confused, is there an expansion valve at that connection? I think maybe the obstruction is there. I thought would be on evap coil behind firewall? But I do see high and low pressure ports there, which confuses me.

I bought All Data subscription and am going through GmPartsDirect.com to try and find a breakdown of that connection but am struggling to find out what's behind that connection, between high and low pressure ports.

cf63c082dfc54e75925a310220ae7c3d.jpg
 
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Matthew Jeschke

Matthew Jeschke

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HA, I think I figured it out. I didn't realize this uses an orifice tube for front and expansion valve for rear. The orifice tube is at the connector. I have to tear it down and see type of debris that has clogged the system :(
 
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Matthew Jeschke

Matthew Jeschke

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I tore it down. The the orifice tube for front AC got plugged. Then the rear expansion valve got plugged. After which the compressor built up so much pressure it blew out the orifice tube.

I cannot seem to find metal debris although some of the debris in the expansion valve is quite suspect as such. However, cannot be picked up by a magnet so I'm not sure what it is.

I ordered a new dryer, expansion valve, orifice tube, and o-rings. I think my compressor is good but hate to waste $100 in parts and refrigerant to find out. It seems the AC had been worked on in as early as 2013 (date stamped on accumlator / dryer).

Here's what I plan to do.

(1) blow out parts as best as possible with compressed air and brake parts cleaner.
(2) Put back together with a new orifice tube and cleaned up expansion valve.
(3) Replace locations where I found faulty o-rings
(4) Charge system with cheapo dust off and run for a while (works great and is cheap).
(5) Test for leaks with dust off in the system - run it for a few days.
(6) Evacuate system. Check the orifice tube and expansion valve for debris.

If clean,

(7) Rebuild with new dryer, orifice tube, and expansion valve.
(8) charge with correct refrigerant and oil as necessary.

I made a video of my diagnosis below. Curious as to what you guys think the debris maybe or where it came from? Also if you think I could go about this another way? I'm not terribly experienced with AC.

Youtube Video of Truck Teardown

Youtube Video of Debris:

I'm moving this thread to here: https://www.tahoeyukonforum.com/threads/identify-source-of-material-clogging-up-ac.111271/
 
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