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No air blowing (heat or cold) after driving a while

After 1/2 to an hour so of driving my 2000 Mercury Sable on the highway, the air almost completely stops coming out of the vents while using the automatic climate control (heat or cold), and the temp drops or rises noticeably. If I switch to vent, the air comes through, and if we leave it there for a several minutes, then switch back to auto, we seem to reset something?, and are able to get heat/cold blowing again for a while, then it cuts out again. Any idea what would cause this? Thanks for your help.

Comments

  • edited December 2009
    Does this happen only when it is cold outside?
  • edited December 2009
    No, it's summer and winter, both A/C and heat.
  • edited December 2009
    This is really just a wild guess, since I can't see the car from here. It may be that your blower speed control assembly (this is what you have instead of a blower resistor pack) is overheating. And, it may be that it is overheating because the bearings in the blower motor are going bad. You may have to replace both.
  • edited December 2009
    It would help us to know if the blower is working correctly. If that is working as it should be when the trouble occurs then the air blend door system may be having trouble. Also make sure the coolant level is topped off so no air bubbles are in the coolant. Another senario could be the coolant is getting pressured up due to a headgasket leak and air is getting into the coolant system. A block check test will show that problem up.
  • edited August 2010
    I have the exact same make, model, and year, and a very similar problem.

    Here are the symptoms I've noticed:

    1) Happens when the car has been driven for more than half an hour. (takes about 60 minutes for me)
    2) Seems to happen just with AC (for me).
    3) You can still hear the fan blowing inside the dash, but almost no air seems to make it to the vents.
    4) Turning off the air for a few minutes helps a little bit, but the problem returns after only a few minutes of the air being back on.
    5) (possibly related) Ice forms on parts of the AC system inside the engine compartment. LARGE pools of melt water will appear under the car after it has been parked long enough after this problem has occurred.

    So, it isn't the blower speed control assembly, since the blower can be heard laboring away as best it can. As a rank amateur, I'm not sure what the "air blend door system" is, but does this sound like it might be related? And, does the ice sound weird, or is it just me?
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