Why does my heater blow cold air even if I set the temp to 90?

Ozz

Ozz

Senior Member
Greetings,
Sometimes my heater works perfectly and then other times, it starts to heat up and then all of a sudden I get cool air (not as cold as the 15 degree air outside, but pretty cold). Even if I turn up the temp to 90, it still blows cold. All the while the fan is cranked up on high.
Sometimes turning it off and back on gets it working right again, other times it does not. Today, I couldn't get it to blow warm air no matter what I did.
Are there any easy (or cheap) things to try, check or do I need a new control unit?

What about a HVAC 'reset'? I read another thread which described how to do it.

Thanks!
 
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Either a problem with the HVAC head unit, vacume leak or air bubble in the cooling system would be my guesses.....
 
How do I get the air bubble out? Is there a plug or something that I can bleed the air from?

Today I put my hand down at the foot outlets and the air is not hot but probably about 60-65 degrees. It feels cold on the feet at full blast though.

Will doing the self diagnostic test help at all?

I looked at the service manual and is suggests checking for vacuum leaks, making sure the thermister tube is still attached to the sensor and checking to make sure the heater hoses going to and coming from the core are hot.

Thanks.
 
i had several rather large leaks in my water pump and had the air bubble issue. its probably the infamous air bubble. in the middle of the crossover pipe, there is a plug that with a 1/4" drive rachet, you can loosen. I cant remember how to do it exactly, but if you search the forums, you shall find the way.
 
I had identical (or very similar) symptoms. I did have one additional symptom: The temperature gauge needle would occasionally shoot up toward the "H" (hot) end of the gauge.

I first got rid of the air bubble. No improvement.

I took it to the L-M dealership, and they replaced the temperature control unit. That did not fix it.

Finally, took it back to the L-M dealer, and they replaced the water pump. The heat works perfectly now.
 
When should I bleed the cooling system of air - once the car is up to temperature?

Why would an air bubble keep coolant from flowing through the heater core?
Is the heater hose the highest point or something?
 
I opened the bleeder plug on the top of the crossover tube this morning and I saw no coolant so I filled it and then backed the car out into the driveway where it would be on an incline and ran it until fluid and some bubbles came out. I have not driven the car anywhere but I am hoping that my problem is solved (for now since I don't know how the bubble got there)

Thanks.
 
Open that plug on the cross over tube.

If it is empty.....fill it.

Run the car until HOT.

Repeat.

Once it is ALWAYS full.....try your heat ;)

KillJoy
 
I think my problem is fixed. Before I had to crank the temperature up to 75 or so to get warm (and sometimes higher - and sometimes heat never came) but now I am sweating when I set it at 69...

Thanks.
 
You burped it?

I'm gonna have to do that this weekend, I'm getting the same thing. My temp guage never goes high so I guess the air is around the heater core?

I get hot air when I give it gas. :)
 
Mine did this durring our full week of sub 20* temps. Just once thou. I got Temp was 1/4 of the way up and no heat. I was mad so I floored it. Then all of a sudden I had heat.

I've also noticed when I start the car in the morning I can softly hear "bubbling" under the dash. My guess is its coolent moving.
 
Stuck thermostat would be my guess.
Wife Exploder had same problem this week. Little heat and no temp on showing.
New t-stat we have heat and 1/4 up.

Oh, and no *****y wife.
 
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