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2002 Silverado heater/cool control

boppascottboppascott Posts: 37
edited September 2017 in Chevrolet
earlier this summer I had problems getting cold air from myA/C to come through the dash vents until I switched back and forth between hot and cold several times now I only get warm air when it is on hot. I ask you if anyone knows if it could be a stuck door or maybe the switch its self? It is the plain jane blue for cold and red for hot...THANKS!!!


  • 0patience0patience Oregon CoastPosts: 1,712
    Most likely there is something stuck in teh blend door.
    Turning it hot to cold moves the blend door and probably moves what ever is stuck a little to get cooler air.
    It could also be the blend door actuator may have stripped on the cold end of the stroke.
  • thank-you Opatience
  • 0patience0patience Oregon CoastPosts: 1,712
    Please let us know what you find. It may help someone later on.
  • boppascottboppascott Posts: 37
    edited September 2017
    the actuator seems to be working o.k, the blend door works fine I am going to change the thermostat to see if it helps even though the temp. gauge says 195 degrees
  • 0patience0patience Oregon CoastPosts: 1,712
    If the blend door and actuator are working fine, then the thermostat isn't going to make any difference.
    You will need to check your AC pressures to see if you are low on refrigerant.
  • boppascottboppascott Posts: 37
    edited September 2017
    the A/C freezes me out .The heater only blows warm air even yesterday .It was 92 degrees here....thanks
  • 0patience0patience Oregon CoastPosts: 1,712
    Oh! I misunderstood/ misread.
    But the heater controller, actuator and blend door still controls the temp that comes out of your heater vents.
    So if the vehicle operating temps are 195 degrees, then either you have a plug in the heater core or the heating system is having fits.

    One thing you might try, as it would help determine if it is a module problem or not, is to get the vehicle warmed up, turn the heater to full heat. Is it luke warm? If so, turn the vehicle off, restart it and recheck the heat.
    Did it get warmer? If so, you have a heater controller problem.
    Restarting it will reset it.
    Sometimes it works, sometimes not.

    If both heater hoses are hot, then you have flow through the heater core and the coolant isn't likely the problem.
    That's not to say it couldn't be, but it is less likely.
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,701
    edited September 2017
    Does the heat blow through the heater vent onto the floor with hot air? Does the AC blow cold air there if
    the mode is set to heater and the temperature is on COLD? Are you able to change the air temperature
    on the floor with the blend door changes? Are you able to change the blend door settings when the air flow
    is set for defroster?

    Part #21 is the mode door that changes from floor, midvents, defrost, and directs the air flow.

    Part #22 is the blend door which modulates the amount of air that goes over the heater core and
    mixes it with the general air all of which goes through the AC coil and is cooled IF the AC is activated.

    If you take off a plastic shield under the dash, if there is one, you can watch the two motors work while you or someone else changes the settings on the dash--with the key on and motor running most likely. On most of the motors on my Buicks the rotating parts were white and showed up easily to see if they were stuck.

    I do not know if this is a problem with those motors, but for earlier H-bodies the axle in the motors could have the gear inside slip on the axle. This meant the gear wouldn't pull the door to the full extent of its travel.

    A quick way to test for the heater core being clogged is after engine is up to temperature turn the HVAC on heat with the blower on high for a few moments in heat then touch the two heater hoses and one should be cooler than the other by a little from the heat it gives up as the water flows through the heater core. IF THE HEATER CORE IS BLOCKED, the temperature of the water coming out will be much cooler because it's flowing through the core slowly and giving up most of its heat above outside intake temperature.

    Testing the AC for charge can be done similarly by touching the inlet and outlet to see if the outlet is relatively close in cold to the inlet temp.

    Be careful of loose clothing while reaching in and around a running engine.

    As Opatience says, it's not your thermostat.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • I will check everything thank you!!!!
  • boppascottboppascott Posts: 37
    edited September 2017
    I think I found the problem,unfortunately one heater hose running through the firewall is cool while the other one is hot when the heater is on full blast and the air blows correctly when I change the settingsThe youtube video shows me that it's not going to be fun changing the heater core!!Thanks for all or your advice everyone
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,701
    edited September 2017
    You might do a little more diagnosis on the heater core. try slowing the air in the heater to lowest speed. Then run the hot engine for a minute or so at 1500 or above rpms to see if the exit hose on the heater warms up any. That will tell you the degree of blockage.

    Was the DexCool in the cooling system discolored with a goopy brown sludge? That means someone contaminated the system with the old green coolant--not the new green that is compatible with all types of coolant. The problem is not the DexCool but that sometimes the old chemical type coolant was added which interacts with the DexCool in a bad way.

    You might be able to remove the heater hoses and run water from a hose in reverse to try to flush out the blockage. The rest of the system needs to be drained and purged of the sludge first. Do not put the hose directly against the tube for the core or you'll apply too much pressure to the tubing.

    If you're not into fiddling with it over a period of time to clear the sludge, you may be happier just to do the replacement, especially if you've got a video for that model. But on the Bonneville and leSabre forums folks did clear it up and some lost the battle.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • I drove it for 20 min then let run for a bit, I replaced the water pump & coolant last year and was thinking about back flushing it. I will try the low fan speed you talked about and thanks for the advice on not putting the hose directly on the outlet fitting-Thanks again
  • 0patience0patience Oregon CoastPosts: 1,712
    Agree with @imidazol97 great info there.
    Before you pull the heater core, you can try back flushing the heater core.
    It's a "hail Mary" attempt, but the blockage might flush back.
    The cooler hose is the outlet hose.
    They make a kit, like Prestone Flush 'n Fill Radiator Cleaner Kit that you can put a T in the heater hose and flush the entire system.
    You don't want to try putting direct water pressure on the heater core, because it is possible to blow the seam on the heater core and you don't want that.

    When you drain and refill, make sure you purge the air out of the radiator, you don't want an air lock, as it will give you just as many fits.
  • Thanks everyone and I have a T
  • boppascottboppascott Posts: 37
    edited September 2017
  • O.K. I took the heater core hoses off of the engine and very little coolant came out of the return hose so I back flushed it and the water flowed easily so I am guessing that it was an air pocket in the heater core . I flushed it out for a few minutes to make sure that if there was anything in there it was gone and it works great. thanks everyone
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,701
    Thanks for letting all of us know what you found. Old rule is to assume the easiest to fix first!

    I don't know if you responded before, but how does the coolant look in the tank? If there's any brown goo appearance or anything like that, do a full flush on the system even if you use a DexCool friendly flush compound that you run and then rinse out again or neutralize. If doesn't take much in the way of aged DexCool that's never been changed or contaminated DexCool with the old style green coolant, usually the cheapest in the store.

    With the heater cores in some H-bodies, folks would have repeat problems. So some prevention may be good.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • I changed the water pump last year along w/the coolant,thanks
  • 0patience0patience Oregon CoastPosts: 1,712
    Thanks for letting us know what you found.
    Glad it worked out for you.
  • boppascottboppascott Posts: 37
    edited October 2017
    you're welcome...the more information that is out there the easier it makes it for the next guy
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