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This morning after running the car for 2 miles, my car was still blowing freezing cold air. I messed with the temp knob moving it all the way cold to all the way hot a few times. Then I started to get warm air. It happend again tonight. This time I had to turn off the car and turn it back on again. What could be going wrong? Where do I start?

This is on a '98 Chevy Malibu.

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First thing to check is the coolant level. –  mikes Oct 25 '12 at 23:21
    
I just topped off the tank –  Mike Wills Oct 26 '12 at 0:34
    
Don't forget to check the level again after you've driven the car until it got properly hot and the thermostat opened. Depending on the car and outside temperature, that's probably a good 8-10 miles. –  Timo Geusch Oct 26 '12 at 15:26
    
Did you check the heater hoses? See if they are hot on both hoses going to and from the heater core. I've had a thermostat get stuck before and then open up, but admittedly that is something rare. –  James Drinkard Nov 15 '12 at 7:11
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4 Answers

up vote 0 down vote accepted

Turns out I was just low on coolant. Once I filled the tank it was fine again.

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2 miles isn't enough for some cars to heat up, is this the first time this has happened?

First, check your coolant level, cold and hot. If it's good, You likely need a new thermostat, the piece that controls the flow of coolant to the radiator. If that doesn't fix it, then check the heater valve as FossilizedCarlos mentioned.

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I wasn't worried about a warm car, but the blowing cold air which should have been at least warm. I think it was due to low collant. I need to find where my coolant leak is. –  Mike Wills Nov 5 '12 at 2:19
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I've got a mitsubishi, so it's a different car, but there is a motor that opens and closes the heater door. It's going out, so sometimes I can hear it click and either engage/disengage when I turn the heat dial, so it's an erratic problem. Could be something similar on your car.

Right now it's not engaging, so it's blowing cold air, even though the heater itself is working fine.

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This is a very common issue. One thing you can do turn on the key (but don't start the engine) and turn on the heater on with the fan on low. Listen while you move the temp control knob. If you hear a clicking sound the servo is shot. –  NitroxDM Nov 4 '12 at 18:16
    
I just replaced the motor, it's a stepper motor, but mitsubishi calls it a motor-heater control. It fixed my issue. –  James Drinkard Nov 15 '12 at 7:08
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Find the location of your heater valve, and see what the temperatures are like on both sides. Might just need a new heater valve, which allows coolant to flow to heater.

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I suppose I need to wait until I have the problem again to test that. It doesn't happen all of the time. (Just twice so far.) –  Mike Wills Oct 26 '12 at 13:23
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