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GMC Jimmy Heating and Air Conditioning Problems

My jimmy just started blowing cold air at idle and slower speeds, but when I get up to higher speeds (50mph) or more it blows warm or hot air. I also noticed that my 4 wheel drive don't work either, not sure if these problems are related.

Clueless and not a mechanic,



  • Any problems with your A/C ... talk about it here.
  • Ok here is my problem. Its going to sound very strange. A/C works decently at night. blows around 60F. During the day im lucky to get 65F. The strange thing is, The higher the fan speed ... the hotter it blows. the lower the fan speed the cooler it blows. I checked the compressor levels, i have everything in the green on both high and low side. All my pipes going to and from compressor/accumulator are cold and sweating. Anybody have any ideas ? Could my A/C be sucking hot air from somewhere ? IM totally stumped. Any ideas are welcomed.
  • jglongjglong Posts: 1
    My '03 Trailblazer constantly reads inaccurate actual outside temperature. For example, here in Oklahoma we've had 30+ days of 100 degrees or higher, but my Trailblazer never reads more than 50 degrees. Consequently, my A/C sucks.

    What do I need to replace/check?
  • repairdogrepairdog Posts: 948
    Never said year but yes the recirc door could be stuck or actuator bad. If you have climate control there is also a blend door - with AC problems I go to the shop after checking connectors - too many interlated problems. But also check the vac hoses under hood on drivers side for rot - the lower one Ts off )plastic one) to the AC.
  • repairdogrepairdog Posts: 948
    There is a temp thermistor believe up by the radiator (is on Blazers) that feeds the readout and if bad or way out of cal will screw the AC up.
  • My 2000 Jimmy (97K miles) heat does not work. Only ambient temp air blows out. A/C works fine. Checked temps on all Radiator hoses and hoses going in and out through fire wall. Temps from 130 - 200 degrees. Thus, some heat should come out. Checked with vacuum gage that the all vent doors worked. No apparent problems. Pulled front dash off and can see the blender door motor pin rotates when the temperature adjuster is turned from hot to cold and back. No change in air temp though. The amount of air flow does decrease when changing temp knob from cold to hot. Thought is the blender door is stuck or broken. However, getting to the blender motor looks like a challenge. Any advice on what the problem may be and what to do next.
  • I have a problem with my Jimmy. When I turn on my ac the ac compressor turns on but there is no air coming out of the vents. Sometimes the air will blow for the first 3 minutes when I turn on the ac but it will always turn back off and I can still here the compressor on. Anybody heard of this before?
  • Sorry, sounds like the classic clogged heater core so no water flowing thru it - have to flush and hope it doesn't leak or blow a hole - another Blazer defect, oh did I say that - Dex cool should be flushed evetry 3 years min and any air in the system it gels up. Search on clogged heater core and I've posted the flush several times. Good luck cause the heater core is dash out and over $500. No help after 5/75 or so by GM but if before for others they pay half if you ask for zone to review.
  • Take it an AC shop and have them look at the R134 level, could be low, the pressure switch bad, or a loose connector. Not easy without AC gauges to find. If 97 and over 80-90k miles the compressors blow the front seals, another GM quality part so get a NEW compressor, not rebuilt or it will die within a year.
  • Last spring the A/C was only putting out a little cool air so I bought a can of R134 w/leak detector and everything was fine. This fall after using the heater for a couple of weeks the weather got warm again, A/C isn't cold again. Put in another can of R134 w/leak detector, cleaned around hose connections and compressor, no leaks found. Stayed cool until we used the heater again. Anyone have any ideas?
  • Something is very wrong with my 98 Jimmy's climate control. It keeps going back and forth between hot and cold and it sounds like it is changing back and forth between recirculating and bringing in fresh air. Even when I turn the dial to off, it continues to make the sound like it is switching back and forth. Anybody have any ideas?
  • If the auto climate system with temps on the dials then you have an additional electric blend motor that swings the heat air door to maintain the temp and it has a plastic gear that can get stripped and if your battery died recently can get lost or not know where it is so searches. Dealer can reprogram or replace and I suggest them as most other shops have not done these and it actually runs much more.
  • Yeah, one of the battery terminals had worked lose just before it started happening. Thanks a bunch
  • When I started my '95 Jimmy yesterday morning the heater fan was on and blowing, so I turned it off until the car could warm up. When I went to turn it on again the fan didn't come back on. No noise, no fan , no nothing. I checked the heater fuse and replaced it, but no luck. Any ideas?
  • Probably the fan motor died - cheap part to replace from underhood and believe only 3 small bolts - all stores sell them. Also possible fan resistor mounted by AC box but thats speed control so fan should still be on at some speed.
  • My 2000 Jimmy stopped blowing air. I have heat and defrost, just no air movement. I'm not sure where the blower motor or blower motor resistor are located. On this model they seem to be hidden by a sealed black plastic shroud that must be cut open. Is the motor resistor located within that black plastic shroud or is it mounted somewhere on the firewall?

    Thanks in advance.
  • jnohrjnohr Posts: 2
    My 2001 Blazer just suffered the same fate. How do we get to the fan motor?
  • repairdogrepairdog Posts: 948
    Resistor is under that plastic cover - cut to access. The fab motor is accessed underhood on pass side.
  • mkobmkob Posts: 10
    I have a 99 GMC Jimmy with 122k miles, this vehicle has never had a/c problems up until 2 days ago. Our temp outside is 96 and when I went to use my a/c it blows warm air. I checked the charge and it is fine, all hoses are in great condition and fan is working. I kept running the a/c trying to figure out what the issue was and finally after 17 minutes the cool - not cold air came out. What could be the reason?
  • repairdogrepairdog Posts: 948
    Pressure switch problem or loose connector (check one on rear of compressor under the air intake) or the comp is leaking or clutch is failing.
  • jlflemmonsjlflemmons Posts: 2,242
    Cheap trick on the pressure switch. If the compressor is not turning, not just the pulley, but the whole thing, disconnect the harness from the pressure switch and jumper the contacts in the harness with a paper clip. See if the compressor comes on, is quiet, and cools. If it does, probably a bad pressure switch.

    If it is really noisy, doesn't cool, and you are sure the freon is still in there, I am afraid you may have a worn out compressor. HOWEVER, on my '99 Blazer, the same thing happened and testing showed it was down on freon. Charge was added and a leak test performed. No leak, and two months later it is still working great. The ac guy had the right attitude. Instead of "you need a new compressor", he took the logical approach. "This sucker is eight years old. Some of the freon is going to leak out sooner or later. And this particular system doesn't have that much in it to begin with."

    I like a mechanic who can think logically. :)
  • tsg3313tsg3313 Posts: 7
    I have a 97 jimmy that the ac is not cold. The compressor comes on every 10 seconds or so because I see the clutch engage. I added about 1/2 can of r134a and checked for leak, and found none, any ideas?

  • repairdogrepairdog Posts: 948
    Take it to an AC shop for a test and probably the pressure switch or a loose connector.
  • mkobmkob Posts: 10
    Thank you for the suggestion. I found it was a combination of putting a new belt tensioner on and adding more R134. Even though I did the test for the pressure and it showed I was fully charged I guess my tester was bad. Good news it was not expensive to fix and I did it myself.
  • jlflemmonsjlflemmons Posts: 2,242
    I love it when it works out right. My gauge showed my system to be fully charged also. It was a little over a half pound low, if I recall correctly.

    Now it will make ice cubes!
  • moldygmoldyg Posts: 4
    Hi there, i have a 2000 gmc jimmy and my heat stopped working the other day and now it seems my truck seems to be running hotter then normal. And ive been hearing this gurguling noise coming from the passenger side? just wondering if its my heater core or something else? thanks fo your help
  • jlflemmonsjlflemmons Posts: 2,242
    How many miles on the Jimmy, and have you ever had the coolant replaced? The gurgling you hear is coming from the heater core. There is air in the cooling system and that will cause the engine to overheat.
  • moldygmoldyg Posts: 4
    i have about 115,000 kms on it. Since ive owned it its never had the fluid replaced...ive owned it for 3 or 4 year
  • repairdogrepairdog Posts: 948
    You have a clogged heater core with the sound and lack of heat OR you are very low on coolant. Dex cool becomes sludge and if not maintained actually eats the core and radiator, clogs the factory cap, and the thermostat. Get that system completely flushed and refilled changing the cap and thermostat. I would first check the system for leaks with a free use pressure tester and see if after you pump it up to 16 lbs it drops and where. 4.3 is known to get lower intake gasket leaks by 100k miles so look carefully along the lower intake to block mating surface, at the water pump, and listen for the heater core hissing with the pressure test. Again - change that Dex cool every 3 years/50,000 miles at least - don't you wonder why the GM warranty expired at 3/36!
  • gin6gin6 Posts: 1
    This is my first post,Son has a 1999 Blazer that I bought used 2 yrs ago.After 1 mo.had the radiator flushed twice,I kept getting that overheating smell,but the shop said it was fine.My question is,Why keep useing the Dex Cool if it keeps cloging the radiator and causing slug?I know that there is green,orange&yellow coolant on the market(Very confusing for us 50+ hotrodders).Can we use another brand? Blazer finally quit on my son so we are now tearing into the engine,( head gasket has lrg. split and corrosion between cylinder)and I am having the heads checked for cracks.When we put it back together what coolant is best? Thanks for your input.
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