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Gary, GMC Technician
Category: GM
Satisfied Customers: 15562
Experience:  15 years gm master tech/15 years ASE master tech
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A/C is blowing hot air. Yes, 2002 Yukon, I have tried to

Customer Question

A/C is blowing hot air.
JA: Have you checked the coolant level? Have you checked the hoses for leaks?
Customer: Yes
JA: What is the model/year of your GM?
Customer: 2002 Yukon
JA: Are you fixing your Yukon yourself? What have you tried so far?
Customer: I have tried to recycle the power by pulling fuses from box under the hood and in drivers side dash. The first attempt, I disconnected the battery. It fixed the issue wit the vent controls, but now it is just blowing heated air. This post does not mention disconnecting the battery. I just need the correct cycle to recalibrate the control module.
JA: Anything else you want the mechanic to know before I connect you?
Customer: It is hot outside.
Submitted: 1 month ago.
Category: GM
Expert:  Peter Bagley replied 1 month ago.

Hello and welcome to just answer and allowing me to assist you. A couple questions to get a picture of whats going on please.Does the A/C compressor engage, have you had an A/C performance test done on the A/c system so we can eliminate any mechanical problem first.

Customer: replied 1 month ago.
Mechanically, everything is fine. Two days ago, it worked at 100%. Yesterday, after disconnecting the battery to clear DTC, the vent control was blowing cold air through defrost and floor vents (not face). After recycling the power, vent controls work correctly, but temperature only blows hot. My guess is that I messed up the sequencing by turning on the A/C after the recycle; thus, not allowing system to fully calibrate. I read post on that does not mention disconnecting the battery, rather, just pulling fuses.I am looking for the correct sequencing.1) Disconnect battery (yes or long)?2) Exactly which fuses need to be pulled?3) Reconnect batt. and run without fuses (and how long)?4) Replace fuses and run for how long before attempting to start the air?
Expert:  Peter Bagley replied 1 month ago.

yes you must do this procedure to initiate the climate control. Preferred Method (w/ Scan Tool)
Clear all DTCs.
Start the vehicle.
With the scan tool, initiate the Motor Re-calibration feature of the Heating and Air Conditioning 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 self-calibrating. If interrupted, improper HVAC performance will result. Alternate Method (w/o Scan Tool)
Clear all DTCs.
Place the ignition switch to the OFF position.
Connect all previously disconnected components.
Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
Install the HVAC/ECAS fuse.
Start the vehicle.
Wait 40 seconds for the HVAC control module to self-calibrate.
Verify that no DTCs have set as current DTCs. hope this resolves your problem this has to be done when ever you replace or disconnect you battery. If you require further service I;ll be happy to do so.

Customer: replied 1 month ago.
I do not have a scanner tool, so I cannot check and clear DTCs on my own. Since there are no dash lights on, I assume everything is okay.None of the fuses are labeled HVAC/ECAS, so I removed the Frt HVAC and RR HVAC from the under-hood box; and the HVAC 1 and HTR A/C from dash box for 10 seconds (these are all of the fuses labeled for climate control in the owners manual). Put them back, started truck for 40 seconds and tested air... no joy.I am attaching the diagrams of the fuse boxes. If there are different ones that you want me to pull, let me know.Also, if a scanner tool can do this easily, which scanner is needed? Can the freebie scanner at Auto zone reset the calibration, or do I need a heavy duty scanner?
Expert:  Peter Bagley replied 1 month ago.

I was just giving you two choices that can be done I realize most people won't have the scanner required to do that so you go to step two. I see the hjvac fuse in both pics you sent the first pic is a 10 amp hvac top left, the second shows a 30 amp hvac fuse in the top rt you can try either one in that sequence to see if it resets won't hurt any thing I would try the 10 amp one first.

Customer: replied 1 month ago.
I removed the 30 front HVAC and 30 rear HVAC from one fuse box...AND the 10 HVAC and 25 HTR A/C fuses when I tried the sequence last time.It did not do anything. Air still blows hot.Are you sure I don't need to disconnect the battery for 30 minutes prior to pulling fuses?Also, should I start the truck with the fuses removed?
Expert:  Peter Bagley replied 1 month ago.

no remove the fuse wait about 10-15 sec reinstall the fuse then start engine and wait about 40 sec for the unit to self calibrate. did you try this method with both fuses one at a time?

Customer: replied 1 month ago.
I will try them 1 at a time.Will you please confirm the following sequence:1) Key in the ignition, but in off position2) Remove fuse for 10 seconds3)Insert fuse and turn ignition on4)After 40 seconds of idle, test knobs.I am attaching a picture of my controls. Should they be set to a particular setting during calibration?
Expert:  Peter Bagley replied 1 month ago.

on auto and max direction don't matter and correct sequence

Customer: replied 1 month ago.
No luck.I singled out the HVAC1, HTR A/C, and FRT HVAC fuses. When none worked, I pulled them all again. It now blows ambient air when set to cold temp and heated air when set to hot temps (just like a car with low freon).Anyway, unless you have another suggestion, I will take it to the mechanic in the morning for the scan tool recalibration.FYI, I took it to O'Reilly's and hooked up their top of the line DYI scan tool from Bosch, but we could not find any functions that allowed to reset the motors. Maybe it is only on professional grade scan tools.
Customer: replied 1 month ago.
Expert:  Peter Bagley replied 1 month ago.

I'm sorry this is as far as I can go not being there .Perhaps another expert has a different perspective on this issue and can help you further so I'll opt out so you may get further assistance. good luck.

Customer: replied 1 month ago.
Just to follow up...While plucking out all of those fuses and trying different combinations, I burned out the A/C relay.New relay resolved the issue.
Expert:  Gary replied 1 month ago.

where the terminals on the old relay brown or looked burnt at all ?

Customer: replied 1 month ago.
Not as far as I can tell. Maybe some slight discoloration, or corrosion. I attached a picture.Is there something else I need to be concerned about, or is this resolved?
Expert:  Gary replied 1 month ago.

i would just coat the terminals on the new relay with dielectric grease as these compressors pull so many amps it is best to coat them to keep a good contact with the female terminals in the box and also the dielectric grease will stop fretting from happening causing a bad connection down the road

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