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Chevrolet Blazer Heating and Air Conditioning



  • Does anyone know if a 2001 GMC Jimmy has a Heater Control Valve? If it does, could someone point me to where it might be located. If there isn't one...I have no idea why I'm not getting any heat. The flapper that controls the incoming works fine, the thermostat was changed, the radiator cap was changed, the heater core was flushed and then the entire system was flushed, all debris has been cleared away from the air there anything else that I'm missing? I guess I'll have to cave and take it in to get it looke at...Ugh!
  • Yes, thru the glove box you can get to that blend door.
  • No valve - the coolant always flows thru the core (if not clogged). Is the system in defrost cause thats default with a rotten vac line. Then if Auto climate add the electric blend door thats got a palestic gear.
  • OK - go but a 3/4 to 5/8" adapter at the auto store they all sell them about $3 and pull the heater hoses at the firewall and bypass it - no heat of couse until the core is done and yes they gave you the going price. If you are not going to fix now flush that leaky core with water so the smell will lessen. Then refill the reservior and see if it remains stable. Refill the radiator and the res when cold. Fill res to the hot line and check at same temp everyday to see.

    If it drops and the hoses/water pump do not leak, and lifters tap on startup, most likely the lower intake and again thats the current rate.

    Dex cool requires changing 3/36 and the GM BS of 5/100 causes this. Air in the system creates a mess and the wrong mix (50% correct) causes a voltage diff that eats the core. The GM cap was crap design also so get a Stant plus change the thermostat at the same time. Hope the waterpump doesn't start to leak soon too as all the crap in the system often gets in the seals and bearing.
  • Hey. I have a 98 Blazer that won't blow hot air. Changed heater core, thermostat, flushed the radiator. Now tore out the dash and replaced the actuator only that isn't the problem. The flapper sticks. Any advice on how to fix this problem? Thanks.
  • When you had the heater box apart would have been the time assuming you reinstalled it correctly. You should be able to move it thru the glove box. If in defrost thats the lose of vac default so look under hood at the drivers side last plastic line in the rubber series and see if all 5/32 lines are good to it. If an LT with climate control (temps on dials and auto postions) also have the electric blend motor that is another door.
  • Thanks! Got it fixed now!
  • delbiagedelbiage Posts: 1
    I think I might be having a similar problem.

    I have a 1999 Blazer, Trail Blazer pacakge with auto climate control.

    The system will blow cold, then I'll hear something squeak in the dash and all of a sudden it blows hot. Every 10-15 iseconds t switches, hot to cold. The cycle repeats when the engine is running, regardless of what position the temperature selector is at.

    Is that flapper box bad? Or could it be the control unit? Any advice?
  • repairdogrepairdog Posts: 948
    The electric blend motor (witha plastic gear) is probably trashed and I would strongly suggest the dealer on this - many other shops do not understand these and will actually cost more to determine and change - its behind the glove box and cycles the door between the AC and heater core based on the temp selected.

    Try rotating the knobs to see if the contacts are dirty and this may clean them and see if running at all cold or hot stops the cycling. I never use that auto fan position cause I hate it ramping up and down.
  • jtripjtrip Posts: 1
    Air went cold then hot a couple of times then stayed on hot,
    replaced actuator because it was clicking and new climate control but did not work.
    I talked to dealer and they said they haven't heard of this which I don't believe,if anyone can help Id appreciate it.
    hot air unless I manually turn the door to cold.
  • repairdogrepairdog Posts: 948
    If Auto climate control you have an electric blend door motor also that often fails. Constant cycling of hot to cold. A simply replacement of a $200 part thru the glove box.
  • carprobscarprobs Posts: 1
    I have the exact same problem on my 99 Blazer LT. I discoverd it last fall when I had the AC on and all of the sudden, it would switch over to extreme heat. Then, I realized in the winter when I had heat on, the opposite would happen (AC would kick on). The heat even comes out when I have the fan turned to "OFF." Took it to the GM dealer SIX times last year for the same problem each time and the problem is still ocurring. They replaced the control panel and fan motor. They also said they never heard of the problem and that the system was designed to run on the "auto" function---I told them that I've always used the "manual" settings and never had a problem all these years until now. I even contacted the corporate GM office and they were of no help. If anyone found the fix, please share. It becomes quite concerning in inclimate weather when I go to turn on the defrost and it blows out cold air using the A/C.....
  • repairdogrepairdog Posts: 948
    Post above tells you the common answer. Maybe find another dealer or ask them about the electric blend motor that controls a second blend door on auto climate control LT models - I have a 99 and mine went out and common and it cycles between hot cold even in manual settings. Motor has a cheap plastic gear that breaks.
  • olddocolddoc Posts: 2
    If i can get the dash out and the heater air handler
    exposed can i get to the door near the steering column to repair it without removing the the entire
    heating unit. Any make do fixes that can be done without complete disassembly of the air handler??
    I would welcome a manual wire. My disabled expert
    says the vacum motor is working and he can see it
    move but the door just springs back. The vacum motors behind the glove compartment are ok.
    Obviously i am looking at big bucks that i cannot afford. Any help or suggestions appreciated.
  • repairdogrepairdog Posts: 948
    That air box requires the dash be pulled to get completely out if the internal door is jamming - but have to ask is this an LT with auto climate control (temps on dials and auto positions)? If so there is an additional electric blend motor accessible thru the glove box atop the air box that often fails. If not also look under hood at the drivers side vac lines 5/32" that run to the reservior in the fender and the last T in the system is a plastic line to the heater controls - rotted rubber lines may be causing the door to open then flip back as vac drops due to pressure and default for door is defrost.
  • wnewcombwnewcomb Posts: 1
    My blazer blows constant heat. The heat blows at the highest setting and no matter what I do to the climate control buttons, it still blows even when all settings are turned off. I believe the problem could be the air blend door actuator. I already have the part so that I may replace it, but I can not figure out where exactly the part is behind the dash in order to replace it. If someone could give me a detailed explaination as to the exact location of this part in the vehicle I would appreciate it.
  • repairdogrepairdog Posts: 948
    Are you installing the electric blend motor on an auto climate control with temps in degrees on the dials and auto positions? If so reach up and grab the little tab behind the glove box left side and pull it in then the box swings out and down. Its on top of the heater/AC bow.

    Found some info on another forum and summerized below:
    Remove the vac line that enters and then move the the vac assembly. Remove the electrical connector that feeds the Actuator. With a 7/32" remove the two (2) mounting screws. There is no screw on the back mounting post, just a pin that holds it steady. Pry the Actuator up off the blend door with a screwdriver. Install new one.
  • I have a 1999 Chevy Blazer with the climate control. The problem is with my heat, it never stops. It constantly blows heat out of the vents. I can still change the direction ( defrost, floor, vents) and the speed of the blower, but cannot shut it off. The AC will not come on, the light comes on, but never any cold air, which I am thinking that it has something to do with this. I am looking for any suggestions please. It is hot outside and is unbearable sometimes to drive. Thank you very much
  • I have a blazer with a heater core that got replaced last winter. Since then, it has only blown heat, no cold. It'll switch vents just fine but regardless of where I have the temp dial it only blows hot. The temp dial is just a blue line and red line, no indexed numbers.

    Could it be the temperature dial? I'm not thinking so, but I don't know what voltages to look for to see if its working right.

    I expect it is the temperature (air blend door) actuator, and I *think* I can see where it is. If I understand what it looks like, then if I open the glovebox and move the vacuum controlled actuator I see there, (I believe this one's for the footwell?) then I can look up behind there and see it.

    Is there a way to test the air blend door actuator? Is there a way to get it out without removing the whole dash?
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