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Chevrolet Blazer Heating and Air Conditioning

ssabiessabie Member Posts: 2
Just changed the water pump and the thermostat. Did step by step in accordance with a Chiltons back yard mechanic book. Got all put back together (with no spare parts) was connecting the negative battery cable back up and there was much clicking coming from the passenger side firewall area. Started the vehicle, let it warm up, put the air on max hot and fan speed hi, checked for leaks (none noted) and took it for a test drive. Air exiting the ventilation got extremely hot. Turned the climate control down to 66 (external ambient air temp was 53) and there was no change in ventilation air. Cycled the air positions (floor/dash vents, floor/defrost, floor, dash vents etc.) and cycled the fan speed. No change in temperature. Returned to house, left engine running, checked for leaks (none noted) and turned off the engine. Left it off for 5 minutes, started it back up, turned on ventilation and extremely hot air again, then it went to a cooler temp and right back to desert hot again. There is a clicking or popping type noise behind the dash somewhere. Any suggestions to what the problem may be? Is this a dealer service only fix? In advance thanks for any posts. 4.3 liter 4WD 121000 Miles, 24000 miles with brand new GM motor.


  • repairdogrepairdog Member Posts: 948
    Is this an LT with auto temp (temps marked on dials and auto positions)? If so theres an electric blend motor that can fail and the noise is it searching around for temp. Rotate the dails a bunch of times and hope its buildup crap on them and they clean off, if not plastic gear maybe stripped - use the dealer for this small shops do not understand this one and charge tons while dealer sees them alot. If standard controls check the vac line under hood drivers side that ends in a plastic line that runs to the control head under dash but of thats bad default is defrost.
  • ssabiessabie Member Posts: 2
    Yes, this is a LT. Will try your advice this evening. Thank your very much for your time and assistance. Will post results.
  • bigbear3bigbear3 Member Posts: 2
    I also have an LT which does the same thing but if I turn the dial all the way to cold and the fan all the way up it finally kicks cold air out. When I run the heater it is fine but when I turn everything off it still kicks hot air out. Although I do not have the clicking or popping noise it still will not stop when I turn the heat off. I occasionally here a water sound like coolant is still coming into the heater core. Do you think it is similar to SSABIE? thanks in advance.
  • repairdogrepairdog Member Posts: 948
    Yes, and you also have a partially clogged heater core with the classic noise - air in the system can also make the noise so check that the lower intake gasket is not leaking.
  • stobarstobar Member Posts: 110
    it is blowing blows cold aire and the temperature gauge keeps going up and down. what the heck is going on?
  • repairdogrepairdog Member Posts: 948
    Thermostat probably bad. Time for a radiator flush, new thermostat and Stant cap. Is the fan clutch OK (sounds like a jet if stuck on).
  • rev7rev7 Member Posts: 4
    My 99 Blazer LS won't blow air out of the floor vents. When you put the selector to floor it defaults to the defrost. The defrost works well, the dash vents works well, ac blows cold and the heat blows hot. I had the pressure checked and it is within range.

    It's pretty cold here in Iowa and we could use some heat blowing on our feet. Any help would be great.

    I'm not for sure if there is a switch or a lever that moves the door that directs the air flow. I'm guessing that I have to take the dash apart to fix this - Is that something that is somewhat easy to do? Or is this going to cost me alot to have some shop fix it.
  • rev7rev7 Member Posts: 4
  • repairdogrepairdog Member Posts: 948
    Default for a bad vac line is defrost so open up the hood and on the drivers side check the rubber vac lines (5/32") from the top of the engine by the PCV over to the cannister and the other assorted ones and replace the rotten out ones - the final end one in the series is the plastic one to the heater selector. Probably will have to use some pliers to grab them and they are a black mess due to rot. The cannister one is often bad too and with alittle time a new piece can be put on (its in the fender and a feel to fit job).
  • kcwebmonkeykcwebmonkey Member Posts: 3
    I've already replaced the thermostat, which made no difference.

    The car blows cold air until the temperature gauge gets up around 260, then suddenly drops down below 200.

    Would my next step be to flush the cooling system? I don't see why it would be running hot though.

  • repairdogrepairdog Member Posts: 948
    Hope it wasn't going to 260 before you did the thermostat! How about a new Stant cap - appears that the old one is not holding pressure. Then could be a clogged radiator. Dex cool should be flushed and changed 3/36 and that GM 5/100 info was crap. Air in the system would be another reason for a temp buildup as steam was hitting the temp sender mounted on the drivers side head between the rear 2 plugs. Make sure the heater core flows and see if the 2 hoses entering the firewall are hot and squeeze and see if water flowing. Sometimes due to the high mounting of the heater core air gets trapped in it and you hear gurggling.
  • kcwebmonkeykcwebmonkey Member Posts: 3
    it was staying right around 200 before this week, when i noticed the problem and replaced the thermostat. i'll go ahead and replace the radiator cap as well, and if that doesn't help then i'll look into flushing the radiator/cooling system.

    Thanks for the help.
  • kcwebmonkeykcwebmonkey Member Posts: 3
  • mksweet80mksweet80 Member Posts: 6
    I have a 94 S10 Blazer and it stopped throwing heat replaced the control panel assembly (used) and just replaced the heater blower motor the motor engages and runs but still not blowing like it should..the only time you can feel some of the heat coming in is from the force of the air going down the idea what to do HELP ANYONE!
  • repairdogrepairdog Member Posts: 948
    Heater core could be clogged (flush it), the resistor that runs the fan speed could be bad (believe up on underhood housing so check it replace if necessary), or the control door (heat vs air etc) not moving so check that and the vac lines underhood drivers side - if defrost only thats default for no vac - look behind glove box for the door vac switch. This all assumes engine temp running at normal 195 so good thermostat.
  • dizzyjonezdizzyjonez Member Posts: 3
    Ok...So I've got no heat blowing into my cab, only cold air, when temperature gauge is hot, and even colder air when the temperature gauge is cold. I've replaced the thermostat and flushed the entire coolant system. Flushed the heater core and there were no restrictions in the flow of water. In-feed to the heater core is hot and the outlet is significantly cooler. Where should I start to look from this point?
  • jlflemmonsjlflemmons Member Posts: 2,242
    The baffle door in the duct work. Sounds like it is stuck in the "all cold" position. It is basically just a door that mixes the air coming through the heater core with the air coming through from outside.
  • repairdogrepairdog Member Posts: 948
    Do you have an LT with auto climate? If so luckly you also has an electric blend door that has a plastic gear that often strips out. Get the dealer to look at it - they do these and will actually be cheaper.
  • dizzyjonezdizzyjonez Member Posts: 3
    I do have an LT, however it does not have the autoclimate. As for the baffle door, is there an easier approach to getting access tot his without having to rip out the entire dash. The Haynes book that I currently have has been useless.
  • cj4258cj4258 Member Posts: 4
    on this topic...

    mine is a 2001 Blazer and recently it started blowing a smell of coolant into the cab. worse than that - more like CROTCH and coolant. its disgusting. later it started blowing really humid, damp air into the cab - so much so that i could hardly see out of REALLY foggy windows. its winter, so i'm using the heat. but get this, the heat works. very well in fact. if i turn it over to a cooler temperature, mist starts coming out of the vents.

    just to get around, i'm riding with all windows cracked to keep the humidity in the cab down.

    everyone i've talked to says its the heater core. just got back from a dealership who ran diagnostics and gave me an estimate. it says that an intake gasket leaking coolant is causing heater core failure. calls for intake gasket replacement (59.83 parts and 492.00 labor), heater core replacement (137.03 parts and 492.00 labor).

    my thing is (and i'm probably really mistaken here) that the heater core is obviously working if i'm getting heat. so why does the core have to be replaced? fix the leak, replace the intake gaskets really should be all thats needed here, right?
  • dizzyjonezdizzyjonez Member Posts: 3
    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!
  • repairdogrepairdog Member Posts: 948
    Yes, thru the glove box you can get to that blend door.
  • repairdogrepairdog Member Posts: 948
    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.
  • repairdogrepairdog Member Posts: 948
    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.
  • stang_girl87stang_girl87 Member Posts: 2
    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.
  • repairdogrepairdog Member Posts: 948
    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.
  • stang_girl87stang_girl87 Member Posts: 2
    Thanks! Got it fixed now!
  • delbiagedelbiage Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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.
  • olddocolddoc Member Posts: 2
  • wnewcombwnewcomb Member 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 Member 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.
  • focker1993focker1993 Member Posts: 1
    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
  • ioldanachioldanach Member Posts: 1
    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?
  • answer987answer987 Member Posts: 6
    The heater in my Jimmy is blowing air out but it's not hot at all. It sucks in the winter time. I just put in a brand new radiator. I had it flushed and everything. Can someone please point me in the right direction?
  • mitch16mitch16 Member Posts: 11
    My AC only blows hot air. I don't have a automatic climate control system. It's just the standard round dials that you turn for hot or cold. Do I just need new refrigerant?
  • ital_ticoital_tico Member Posts: 1
    Three days ago, the system have a short circuit and the alarm turn on. Now the short circuit was repaired but three things remains:

    First: when I connect the remote control to open doors then the car open the 4 doors not only one.

    Two: when I connect the lights of the car, the central control of the doors sound like I try to open the doors and is the only way to move the electric mirrors (at the door) to see the sides of the car.

    Three: every time I put the ventilation system in my Blazer LT 2000 the air is very hot, even with air conditioning (probably I need to check this system too).

    Any suggestions... Thanks in advance.
  • jenups07jenups07 Member Posts: 2
    I live in WI and it's getting really cold outside. Well when I turn my heat on with the blower on 1 or 2 it blows warm air if it's above freezing if it's below freezing it's cold. Anything on blower 3 or 4 it's always cold. People tell me it's the heater core and to flush it. But when I looked under the hood the hoses from the radiator go to a canister type thing and then that leads into what I think is the heater core. So if I flush it what is that canister thing and will the flush not work then. I tried looking in my manual for a name for the canister thing and can't find a name I can find a pic though. Can someone help me?
  • jenups07jenups07 Member Posts: 2
    I live in WI and it's getting really cold outside. Well when I turn my heat on with the blower on 1 or 2 it blows warm air if it's above freezing if it's below freezing it's cold. Anything on blower 3 or 4 it's always cold. People tell me it's the heater core and to flush it. But when I looked under the hood the hoses from the radiator go to a canister type thing and then that leads into what I think is the heater core. So if I flush it what is that canister thing and will the flush not work then. I tried looking in my manual for a name for the canister thing and can't find a name I can find a pic though. Can someone help me?
  • jetson2001jetson2001 Member Posts: 4
    I have looked at all the posts for heating problems. I have a Haynes Manual. It shows how to remove and replace items but in the trouble shootiing there is nothing as to HOW to diagnose heater issues (or how to diagnose so may other things as well.)- just bought the Blazer 2 weeks ago. Replaced a 1992 that was totalled just 3 weeks ago- loved that one..... I could afford the warranty for the drive train - but not for other things- electrical etc.Soooooooo we get plenty of air- blows very hard - have moved all the dials etc- still no heat. What should we check 1st?
    Also.... last Sunday the drivers windshield wiper seemed to go "off track" - it is "spastic" in its actions. the passenger one works just dandy- however they are crossing over and getting stuck on each other- Manual only shows how to change wiper blades. Do the wipers have little teeth that could be eroded like starter teeth and that is making it just not catch all the time- how do I get the wiper assembly off to check? and then what do I do with it?
    Thanks so much.
  • toolzztoolzz Member Posts: 4
    I'm having identical issues as message # 49 - I have replaced my thermostat and checked my coolant levels. I have reduced heat in my system coming out of all air supplies.I'm trying to understand if the coolant flow through my heater core is controlled by a proportioning valve to reduce / increase heat or how it is controlled. My assumptions are that the select heat / cool knob on the front of the dash is a potentiometer but I do not not what it is controlling. Any help would be appreciated.
    Dean Arzberger
  • jetson2001jetson2001 Member Posts: 4
    I just had mine fixed at the dealer (see message #52) as I found out that we DID have a 90 day 3000 mile warranty. It was a spring inside the radiator that regulated the water flow- it would work sometimes and sometimes not- so as we did not fix it ourselves I canot tell you the absolute specific details of the particular spring- I am sure we could have never figured that one out- we thought it was the select heatt/cool knob at first that controlled the baffle that opens the heat. Good Luck.
    :} Anna
  • toolzztoolzz Member Posts: 4
    Anna - Thanks for the information. Was the replaced spring in the main radiator or in the heater core radiator ?
  • jetson2001jetson2001 Member Posts: 4
    Dear toolzz,
    The spring was in the main radiator. The heater core was fine.
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