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GMC Yukon Climate Control AC and Heat Questions

109 messages,  Last post on Oct 02, 2009 at 3:30 PM

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What is this discussion about? GMC Yukon XL, Chevrolet Suburban, Chevrolet Tahoe, Heating / Cooling, SUV

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#79 of 109 Climate control issue by scottyd1 Oct 20, 2008 (7:29 am)
I have tried to unplug the battery, pull the HVAC fuse under the hood, and stomp my feet...none of them seem to work.   My problem is that the passenger side and rear AC blow cold, while the driver side blows full heat. I have tried turning the car off...and drivers side blows cold for about 7 seconds...then..back to full heat....while the passenger side blows nice and cold.   This just started after I changed the battery last weekend.   Any other fixes I should try. The dealer wanted $800 for an evaporator and condenser....which is BS....and I have told them so. Replies to this message: arrie (Oct 20, 2008 8:33 am) scottyd1 (Oct 20, 2008 9:38 am)
#80 of 109 Re: Climate control issue [scottyd1] by arrie Oct 20, 2008 (8:33 am)
Replying to: scottyd1 (Oct 20, 2008 7:29 am) scottyd1,   I agree it is BS to say problem is with evaporator or condenser. Not blowing heat has nothing to do with either. Missing heated air means that you either do not have hot engine coolant flowing thru the heater core or the air mixture gate that mixes hot and cold air is not working properly. Since you have hot air coming out from driver's side air vents it kind of rules out missing engine coolant flow thru heater core, right?   There is one thing to check though with engine coolant. Make sure coolant level in the system is correct. I have posted about this before but your coolant level might be much lower than what the level in the expansion ganister under the hood shows. Mine went down to 2 gallons low and I still had level in the expansion ganister.   To check for the coolant level open the expansion ganister gap after a drive when engine is hot just enough to allow the spring loaded valve to open that is built-in the gap. If you see and hear a lot of steam flow from engine to the ganister you might have the same problem I had. When this steam flow stops your coolant level goes down as the engine coolant channels then fill with coolant.   I'm writing about this because if your coolant level is on "low limit" there might not be enough to circulate thru the heater core for the rear seat system. There are two heater cores (like A/C evaporators) separate for front and rear systems so only cool air from rear could be caused by marginally filled engine cooling system. This could very well be the problem since front and rear systems have separate controls.   One way to check for low cooling system is to rev-up the engine and see if you get hot air out of rear vents. Higher engine speed allows water pump to do a better job even with low coolant level.   When my coolant was low I had an odd symptom, which was that air from vents went hot while revving up the engine, like starting from traffic lights. This was very odd when I drive with A/C on all the time. Later when I found the low coolant level it explained what happened.   The automatic climate control system controls air temperature to a set point. When I did not have a lot of coolant flow thru heater core with normal engine speed the air mixture gate opened to hot side more than normal to get air temperature to what the system was set to. Then, when I start from stop obviously with higher engine speed coolant flow thru heater core increased and hot air was blown out from vents for a few seconds until the system corrected it.   Above does not explain the problem with the driver side front cold air though but I wrote about it because you might have two separate issues, which both I have experienced with my '04 Tahoe LT.   Fix for the low engine coolant level obviously is to fill it up.   The other problem I had two times was that when I had my A/C on I had hot air coming out from passenger's side but on driver's side it worked fine.   The first time this happened I was working on the radio and had to disconnect the climate control module. When I started up the car only hot air was blowing out from passenger side. I thought that I had a bad connection or something and for a fix I disconnected / connected the climate control module again and everything was ok.   The second time this happened just like for you. I replaced the battery and right after that only hot air comes out from passenger side vents. And the fix was the same. I disconnect / connect the climate control module and voila, everything works again.   I think when changing battery the climate control module gets somehow messed up because the battery connection makes several sparks while screwing that cable connection in the battery.   After my second incident I read about the removing fuses and thought how silly I was going to disconnect the climate control module but now when you have done the fuses and it does not fix it perhaps my job was not that silly after all.   Disconnecting / connecting the climate control module is easy.   1. You need to remove the bezel around the cluster that also covers around radio and climate control unit. It easily pulls off from some tabs. To take it out you need to have your steering wheel tilted down and gear shifter all the way down, i.e. need to have key in ON position to get gear shifter down. You need to force it a little bit to clear on top of the instrument panel and after it is out turn off the emergency flashers as every time I do it the bezel hits the switch and they are ON. Move gear shifter back to Park and turn key OFF.   2. Unscrew the 4 screws (8 mm socket) from the climate control unit.   3. Squeeze the 2 plastic tabs at each side between removed screws to pull the control unit out.   4. Unplug both harnesses on back side of the control unit and plug them back in.   5. Assembly in reverse order.   Before you assemble everything back you can try if it fixed it and if not perhaps you can disconnect / connect the harnesses again. In my case it fixed it after just one try and while I disconnected / connected the harnesses I had the key in OFF position.   Before doing any other work I highly recommend checking that coolant level the way I explained because just looking at it in the expansion ganister does not necessarily tell the whole truth. You say though that your problem started right after battery swap so it kind of points to direction of control module needing a good reset by unplugging the harnesses in the back of it.   I assume you have the automatic climate control system with 2 zones in front and separate zone for rear seats. My truck is an '04, which is the same I think thru '06.   Hope this helps.   Arrie Replies to this message: scottyd1 (Oct 20, 2008 9:38 am)
#81 of 109 Re: Climate control issue [arrie] by scottyd1 Oct 20, 2008 (9:38 am)
Replying to: arrie (Oct 20, 2008 8:33 am) Arrie..   I will try to reset the climate control module this evening. I will check on the coolant level when I get home from work.   Thank you very much for your advice.   I will let you, and everyone else, know the results.
#82 of 109 by scottyd1 Oct 21, 2008 (4:55 am)
Arrie,   Thanks for the assistance. I removed the module last night, and reset it.   So far, it worked as tested last night, and this morning it was working normal.....so I think it's fixed.   I appreciate the help! Replies to this message: arrie (Oct 21, 2008 8:58 am) eric187 (Oct 25, 2008 4:21 pm) arrie (Oct 25, 2008 4:49 pm)
#83 of 109 Re: [scottyd1] by arrie Oct 21, 2008 (8:58 am)
Replying to: scottyd1 (Oct 21, 2008 4:55 am) Great to hear it works!   How about that coolant level and rear heater?   Arrie Replies to this message: eric187 (Oct 25, 2008 4:21 pm) arrie (Oct 25, 2008 4:49 pm)
#84 of 109 Re: [arrie] by eric187 Oct 25, 2008 (4:21 pm)
Replying to: arrie (Oct 21, 2008 8:58 am) Arrie, I have the same problem as Scottyd1...my driver's side air blows HOT air even when selected to cool ..and the passenger side functions as normal   I read your posting on re-seting the climate module and tried unplugging and plugging it back several times. Is there anything else i can try?   PS...my problem also occurred immediately after installing a new battery.. thanks   Eric Replies to this message: arrie (Oct 25, 2008 4:49 pm)
#85 of 109 Re: [eric187] by arrie Oct 25, 2008 (4:49 pm)
Replying to: eric187 (Oct 25, 2008 4:21 pm) Unfortunately I don't know any other tricks for this.   When you unplugged the two harnesses, you did have them both disconnected at the same time, correct? And you did have your key in OFF position while disconnecting the harnesses?   Anyway, the problem seems to be with the climate control module so to fix it, if re-setting does not work, you might need to get a new (or new used) control module. Of course, it would be nice to be able to try someone else's control module that you know works and see if it makes yours behave as it should. Perhaps a used car parts store, i.e. junk yard, would let you try and purchase it if it fixes your problem. Some of them let you try parts like this.   The problem could also be a stuck temperature control gate that mixes cold and hot air for set temperature but you said that the problem started right after battery change so the problem probably is with the control module.   Arrie
#86 of 109 1998 GMC Yukon heater problem by bobvanleeuward Dec 11, 2008 (2:21 pm)
The heater in my 1998 GMC Yukon works sporadically. Does anyone have any idea why this would happen? Thanks! Replies to this message: arrie (Jan 16, 2009 2:58 pm)
#87 of 109 Re: Bebensee [bbebensee] by B4UBuy Jan 15, 2009 (6:24 pm)
Replying to: bbebensee (Jun 30, 2008 4:46 am) The problem with your rear heater is the doors that were used in most of those units. They were out of spect and were still used. The whole rear unit needs to be removed and either have the doors replaced or regrease the holes and the door pins. It takes about an hour or two if you do it yourself. Depending on your mileage it should be under warranty. I hope this helps.
#88 of 109 Re: 1998 GMC Yukon heater problem [bobvanleeuward] by arrie Jan 16, 2009 (2:58 pm)
Replying to: bobvanleeuward (Dec 11, 2008 2:21 pm) Make sure you have enough engine coolant level. Best way to check this, which is against what they say, is to open the engine coolant expansion reservoir after running the engine hot.   By opening I mean to place a thick shop rag on top of the cap and turning it slowly open to let pressure out from the reservoir. Pressure comes out when the spring loaded valve on the cap opens and lets vapor pressure out thru the drain line. This means that the cap is still on the threads but still be careful not to get hot liquid on yourself.   Allowing vapor pressure out from the engine will let the cooling system to fill all the way. If your engine is not filled all the way you will see the level drop in the reservoir.   I'm writing about this because it happened to me. I still had some level in the reservoir but was able to add almost 2 gallons of coolant to get level really up to the reservoir. Somehow this cooling system can get air bound and keep coolant from filling in the engine, which should never happen.   If coolant level is too low you will not have enough flow thru the heater core and you will see thing happen like it heats when you rev-up the engine but then does not when on idle or during low rpm driving.   Arrie

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