Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

GMC Yukon AC and Heat Questions



  • bbebenseebbebensee Posts: 3
    I still have no answer as to why when I turn on my heater, the only vents that blow warm air are in the front. The back vents never blow warm??????? 2004 Yukon. I have disconnected the battery to default the computer no luck. The fuse is fine. The vents are not plugged the airflow is fine. Again this only happens with the rear climate control.

    CAn some one please help before Winter sets in, last winter was cold!!

  • wilbankswilbanks Posts: 1
    I have climate control. The A.C works sometimes and blows cold air and the it will turn off and A.C button on the bottom of control panel will blink and A.C turns off. And come back on after a while then back off. What is this a problem with the control panel?
  • gwfgwf Posts: 3
    Yep, can confirm the "pull-the-fuse" fix. I replaced the battery in my '04 XL Denali, and the front A/C would only blow full heat (I could control the fan, but the temp seemed to be max heat regardless of the panel setting). The rear controls seemed to work fine. I disconnected the battery a couple of times (key off) thinking that would reset, but apparently not. After reading this thread, I pulled the (front) A/C control fuse (I forget the label, but there's one for the front, and one for the rear), and drove the thing out to dinner. When we came out, I put the fuse back in, and was relieved that the system seemed to return to normal. Never had any prior issues with climate control. Thanks!!
  • rshtrsht Posts: 277
    Just my guess, have you checked to see if your AC system has the proper level of 134a?
  • stearnspkstearnspk Posts: 2
    We took it in and had the problem fixed. It ended up being a small hole made by the screw in the rear mud flap that caused a small leak. It was covered by the insulation so the dye was not visible where it was leaking. Thanks for your help.
  • mefixitmefixit Posts: 1
    Tried pulling the 10 amp fuse under the hood. Didn't seem to work. Is this the only fuse I need to pull?
  • 2002 Yukon XL / AC works great until there is a rain and you drive through a large puddle.

    My 2002 Yukon XL AC works great until I go through a large puddle of water and then the air light on the panel blinks and the air goes off. After a while the light will go back on and the AC blows cold air again.
  • arriearrie Posts: 312
    I'm not sure what light you talk about? Do you mean the "snow flake" on the automatic climate control panel?

    Anyhow, the problem with driving thru a large puddle of water could be that it momentarily disables the AC compressor. How it could do this is getting a lot of water on the compressor drive belt and pulleys.

    The AC compressor is not driven by the fan belt. It has its own belt, which does not drive anything else but just the AC compressor. Location of the compressor is very low in front of the engine. It is actually as low as the crank shaft of the engine (this is how it is in my '04 Tahoe, which I believe is built the same for this part). Being this low in front of the engine makes it very likely to get a good wash if you drive thru a large (deep) puddle of water.

    Your vehicle is 6 years old so the belt could be worn and rather easily slip when wet, unless you have replaced the compressor belt.

    I have not replaced mine but when I changed my fan belt I looked at it and it appeared to be kind of a V-belt. V-belts start slipping very easily if they wear too narrow or the pulleys wear too wide. This causes the belt to "bottom out" on pulleys and the wedging provided high friction forces between walls of the pulleys and the belt are lost. If the belt / pulley condition is borderline a water flush can cause the compressor to stop for a moment until water dries out and this does not always cause belt squeal either. Then during normal dry conditions it works just without any problems.

  • can I change my manual climate control to auto climate control in my 2007 GMC yukon
  • arriearrie Posts: 312
    Your rear vents not blowing hot can be cause by three things (not counting for obvious hose or other leaks in system).

    1. The temperature control does not work, i.e. the gate that adjusts for temperature setting is stuck open on cold side. This could be electrical or mechanical problem. Unfortunately I have nothing to tell about this as I have not had electrical or mechanical problems with rear heaters on my '04 Tahoe.

    You can do a simple test though. While parked rev-up your engine to 3000-3500 rpm and see if with this engine speed you get hot air coming out from rear vents. If you do then you do not have electrical / mechanical problem with rear heating system air mixing. Your problem is that with normal engine running speed you do not have engine coolant circulating thru rear heating core.

    2. I did have a problem with only cold air coming out from rear vents. This happened when I also had engine overheating problem.

    The problem was too low coolant level. I had some level in the expansion ganister under the hood but coolant was very low in the engine. You can easily check for this by opening the cap of the cooland expansion ganister after you drive and engine is hot (to do what the cap reads not to do). By opening I mean to loosening it just enough to let pressure out from the ganister. There is a spring loaded valve build in the cap, which will let pressure out much before the cap is actually opened and it all comes out safely thru the pressure relieve tube. At least this is how mine is built. Put a rag or towel over the ganister before you turn the cap.

    If your coolant level is too low you will hear and see a lot of steam come out from engine in the ganister and at the end of this the coolant level in the ganister will drop. Mine went totally empty and to fill it up I added almost 2 gallons of coolant!

    There are a lot of postings in this site about coolant leak and not finding the leak other than in cylinder head. I think I had this "porous cast" problem and it got fixed after adding some leak fix in the coolant.

    It is a mystery why the coolant level in the expansion ganister does not go down as coolant disappears from the system. It must get air locked or something?

    This is very dangerous situation for the engine as it really can overheat and burn as a result of low coolant level. Lost heat at heater is the first sign of coolant level being too low.

    3. Your water pump could be going out, i.e. is worn out and does not give enough water flow to circulate coolant thru rear heater core. A worn pump would also give flow with elevated engine speed if you do the test that I mention in part 1 above, i.e. the test can indicate either low coolant level or worn out pump.

  • 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.
  • arriearrie Posts: 312

    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..

    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.
  • 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 I think it's fixed.

    I appreciate the help!
  • arriearrie Posts: 312
    Great to hear it works!

    How about that coolant level and rear heater?

  • Arrie,
    I have the same problem as 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? problem also occurred immediately after installing a new battery..

  • arriearrie Posts: 312
    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.

  • The heater in my 1998 GMC Yukon works sporadically. Does anyone have any idea why this would happen? Thanks!
  • B4UBuyB4UBuy Posts: 1
    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.
  • arriearrie Posts: 312
    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.

  • I just bought a 2004 Tahoe for my wife, we could start her car and let it idle forever with no heat. Anti-freeze level appeared correct in resavoir, added 1- 1/2 gallons of anti-freeze and Bingo, now heat will drive you out of car........
    Thanx for the tip..........
  • arriearrie Posts: 312

    You have a leak!

    You probably have the porous cylinder head cast problem that lets engine coolant to leak internally inside the engine.

    I would get BAR's radiator leak fix and pour it in the coolant expansion reservoir. You really need to do something and this is the cheapest fix that I know that at least worked for me.

  • arriearrie Posts: 312
    Little SCARY info for all readers with possible coolant leak.

    A couple of days ago I went to check on the coolant level on my '04 Tahoe engine. I have posted before that after using Bar's radiator fix I stopped loosing coolant as when I look at level in the reservoir it has not gone down.


    What I did was that while engine was running I opened the cap of the coolant reservoir and the level went down by 1 1/2" immediately when I broke the seal of the cap.

    I did not have any steam come out from engine to the reservoir so I was not overheating or nothing like that but the engine definitely was not full of coolant in all cooling channels.


    What probably causes this is a very poor design of the reservoir and its connection in cooling system. It probably is that too small tubing from the reservoir does not allow coolant level in the reservoir go down because the reservoir is sealed, i.e. cannot get air in for the coolant to flow out. The valve in the cap does not let air to flow in the reservoir, only excessive pressure out from it.


    I think I will disable the valve in the reservoir cap, i.e. make it so that reservoir can breath freely in and out. Perhaps there is a check valve that could be installed on the cap that would let air freely in but outgoing pressure would still need to work thru the valve in the cap.

  • ok, the blower still works,but the vent selection knob will not change where the air flows and the a/c snowflake light button does not turn on the a/c.when you hit the button to turn on a/c it feels like the vent just pulling in outside air.The recycle but also does not come on to recycle the cabin air.I have checked all fuses ,they are all good.all levels of the blower switch works,just not the position select switch or the buttons.please help!
  • (1) Two months ago, the front AC only blew on "5", not 1 through 4. The rear AC works fine. Is it a switch issue!?

    (2) Went out to the truck today and the AC blower was running when the truck was off, keys in hand?!?!

    (3) I took out a 10 amp AC fuse and killed the front AC. Rear still works great.

    What are your comments with regard to these three issues?
  • 2000 tahoe 5.7 old body style. Blower fan just quit the other day. Have checked fan by straight wiring to 12 volts, it works. Replaced resistor and relay behind glovebox. Checked all fuses. Don't know where to turn now.
  • jking5jking5 Posts: 2
    When the AC on my 2004 Yukon XL is running, sometimes the heat comes on...just on one side, while cool AC continues to blow from the other side? Any suggestions besides taking it to the dealer's. Warranty has run out and can't afford their rates.
  • arriearrie Posts: 312
    I have posted about this before a couple of times. I had the same problem with my '04 tahoe and I fixed it by disconnecting the A/C control unit wire harnesses.

    Easy job to do. Take the bezel out and unscrew the 4 screws. You need to hold the clips on both sides to pull the controller out. Disconnect harnesses at the same time and then replace all.

    Worked for me.

  • Thanks for the help. Pretty straight forward job except for disconnecting wiring harnesses. Not a lot of room to work with. Blower is working fine at the moment.
  • nana15nana15 Posts: 1
    I have a 97 yukon, the rear cool air stopped working and the front does not seem to blow that cold. I have had coolant put in and it checks fine.The rear just blows hot air,it is ac only in the back. Can someone help?
Sign In or Register to comment.