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Chevy S10 - GMC S15 and Sonoma Climate Control



  • the_big_althe_big_al Member Posts: 1,079
    It seems that my heater is taking awhile to get warm. I have a 2001 4.3 V6 S-10. It used to be that the heater air would start getting warm as soon as the temp gauge moved past the 100 mark on the temp gauge. It only took maybe a mile of driving before it was warm enough to turn on full blast and not be chilled by the air.

    However, just recently the air won't get warm at all until the temp gauge reached 210 (midpoint) and then it would go from cold (not lukewarm, not even cool, but mostly cold - as cold as the outside air), to almost instantly hot. Almost like if you were to turn the cold water off on a faucet at the same time you were turning on the hot water. What is it that controls and regulates the airflow from hot or cold? Is there a valve somewhere that opens and closes? That is my first thought because the heater air is eventually hot. It gets as hot as it should and always has, it just takes until the truck warms all the way up to the midpoint temp which is 210. After that it stays warm, even if I shut the truck off for a couple of hours and come back later. As long as the temp hasn't dropped all the way back down to below 100 the heater stays warm.

    I should also note that I a while back, the switchover from floor to dash to defrost started taking a little longer as well as it seemed that the switch from fresh to re-circ A/C wasn't always happening. Again I have figured a slow moving valve and for the most part those switches always happen and I was able to mostly solve the recirc to fresh air switch by having moving from one to the other repeatedly and it seemed to "correct" the issue to the point that it is certainly usable but not and instant switchover from one mode to the next. It takes several seconds to switch from one mode to the next.
  • gonogogonogo Member Posts: 879
    The heat is controlled by a electric actuated door. It directs air through the heater core for heat and outside air for cold. Usually when door motor breaks you stuck in one mode. The heater cores have been known the plug, usually it give low or no heat.
    Reverse flush is the way to clear a heater core, from the pump side out the head side.
  • the_big_althe_big_al Member Posts: 1,079
    but what if I have good heat eventually?? The heater will get hot as soon as the temp reaches the 210 operating range, just not until then. It used to gradually warm up until then and was warm enough to operate as soon as the needle moved past the 100 mark, but not it stays completely cold until the 210 mark.... the system I'm sure needs to be flushed as it's been about 4 years since it was done so maybe that's the issue. Too bad the weather is trying really hard to warm up otherwise I would be more worried.
  • the_big_althe_big_al Member Posts: 1,079
    Here's a truly odd one. I think I solved the heater issue I was having though. I checked the coolant level and found that it was low. I added more coolant and all seems fine now. It is time for a coolant flush though. All three of my vehicles need it as well as 2 of them need an oil change... Looks like a good half a days work.

    Anyway, I am experiences a quirky turn signal. It is on the driver's side. It only happens when the lights are on and then only intermittently. When it happens it acts like a bulb is burnt out with the fast and short blinking. Only there are not any bulbs out. When it has happened, I have gotten out of my truck to see what is happening. The front seems fine. However, the rear lights are where the quirk is. When the turn signal is on the bright lights up, but near as bright as it should. When it goes of, the reverse light, driver's side license plate light and tail-light illuminate. Then alternates back to a not as bright turn signal.

    It's hard to explain... maybe I'll try taking a video of it when it happens again and posting it. But at this point I am at a loss as to where to even begin.... :confuse:
  • atls10atls10 Member Posts: 1

    I had this same exact problem and after trying a few things it ended up being the clutch on the A/Ccompressor. Once you replace this you'll be good to go, I haven't had a problem was an immediate fix. Hope this helps.

  • grumpyoldfartgrumpyoldfart Member Posts: 4
    My 2001 Jimmy has the same problem. The AC works great, plenty of heat but can't switch between defrost and floor. The problem was a broken shaft on the air door. This is the one controlled by the air motor directly above the accelerator pedal. It has two vac lines (red and blue) running to it. That's the good news. Bad news is repair requires removal of the dash board then the assy that houses the heater core. No easy task - takes many hours. I will attempt to photo sequence and post as I complete this repair.
  • grumpyoldfartgrumpyoldfart Member Posts: 4
    As of 12-12-09 Rock Auto had them for less than $13.
  • grumpyoldfartgrumpyoldfart Member Posts: 4
    The air control flapper inside the heater box is broken. It's the one controlled by the vac motor with red and blue lines.
  • grumpyoldfartgrumpyoldfart Member Posts: 4
    See this forum for diagrams and instructions.
  • abstalini429abstalini429 Member Posts: 1
    a man just read this post, the relay is the lil silver box just 2 the rite of ur motor, if that is fine follow the wire to the firewall and check the resistor switch
  • boat567bboat567b Member Posts: 1
    hello im having problems with 2001 s-10 .as the heater works great .but controls will not change from floor to defrost .it blows out both floor and defrost all the time no matter where i have the control. could this be the .control knob or a vacum issue i noticed there is 4 vacum assy . i think it is not the temp control.control. o took glove box out i can see it working ok all though i see a vacum ball right there in same area. that seems as soon as i start the egine . it pulls all the way open ? i have no clue to go from here . i do see it looks like 2 vacun balls down by floor on drivers side .. can any one help thanks bill b.
  • the_big_althe_big_al Member Posts: 1,079
    I think you have a stuck baffle somewhere. I know on my truck, also a 2001, it takes a few seconds to switch from mode to mode. It will take several seconds to switch to defrost and then back to dash vents and then to floor vents. I think it is because the baffle that directs the air into each location is sticky. I don't know where this is or how to fix it, but I think that might be your issue.
  • tucsonbilltucsonbill Member Posts: 1
    I have the same problem with my 2001 GMC Sonoma. Plus the blower (or something associated) starts sqeeking - especailly if I make a right-hand turn. Pretty weird! Perhaps the blower motor resister for the fan not working in first two postions and a drop of oil on the motor shaft? Is any of this halfway easy to get to?
  • sonnyfsonnyf Member Posts: 1
    I have a 2003 Chevy S10 with heater control problems, the heat will not switch from dash to floor or from dash to defrost. I tried looking up under the dash to see if I could see the control arms but everything is covered up.Any advice on how I can get to it to see if the flapper is stuck?
  • sandbermsandberm Member Posts: 1
    Did you fix this yourself? If so, what were the part #'s and how much did it cost? Where did you buy the parts? Thanks
  • dlt1558dlt1558 Member Posts: 1
    edited July 2011
    I was replacing the fan switch in the control module and the plug that allows me to switch from floor to dash vents came unplugged. I cant seem to find where it plugs back into.... Any help would be appreciated. This is in my 92 SLE
  • 1990s151990s15 Member Posts: 2
  • 1990s151990s15 Member Posts: 2
    On my 1990 S15, it seems like the volume of air coming out of the vents is extremely small. When the fan is on setting 1, there is almost nothing coming out of the vents. When it's on full, there is very little air coming out. Also, the floor vent is always open no matter what setting I have it on (Max A/C, Norm A/C, vent, HTR) and there is more air coming from the floor vent than there is from the dash vents. I'm assuming all the doors work properly because I can hear them moving. Someone told me that this is how these trucks were made, I don't believe this.
  • mrrosemrrose Member Posts: 1
    It is behind the glove box. Open the box and the stop is spring loaded so you can push it out of the way. be careful as all glovebox contents will spill on the floor.
  • sulley1sulley1 Member Posts: 1
    I have a 98 Blazer with AC, i can not controll the tempeture it is on high heat all the time, the AC/heat controlls work fine but i can not turn off the heat with the tempeture controll knob. Thanks for any help. Sulley
  • gonogogonogo Member Posts: 879
    4/09 wow. Most likely blend door motor is bad. You can try pulling the HVAC fuse or disconnect battery to see if it just need a reset.
  • taber33taber33 Member Posts: 1
    edited March 2012
    I have a similar problem with my 2000 Sonoma, but instead of it being stuck on one set of vents it is skipping over the floor vents n goes right to defrost... How could I fix this?
  • redstartnhredstartnh Member Posts: 1
    The blower in my 2004 GMC Sonoma has stopped working, that is, a couple of weeks ago it started to make clattering noises at the highest speed, now there is no "fan running noise" and no air pushing through at any setting, although there is warm air being produced (I want to defrost my windshield). Does it sound like something a novice DIYer could take on? Where should I start?

    Thank you!
  • clr_welderclr_welder Member Posts: 1
    Bet you have a vacuum leak. Your heater is controlled by vacuum, and acceleration will give you more vacuum. There is a bundle of wires that come through the firewall, about center, down 9" or so from top of it, in that bundle is a vacuum line. If it's hooked to thin air, or you have a rotten vacuum line in your system, you'd get that effect.
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