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Heater not working

Tiny
ETERNALARIANNE
  • MEMBER
  • 1987 CHEVROLET CELEBRITY
  • 2.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 200,285 MILES
I have this car that when I turn the heater on, it just blows cool air. Sometimes it will get ever so slightly warm but most times just cool air.

I checked the metal coolant lines that run to the heater core. They get warm and even hot, except the ones immediately before the heater core stay cool. Could it be a blockage or is it supposed to be like that?

I have already replaced the thermostat and temperature sensor fixing other issues. Fuses look good as well. What else can I check?
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Friday, February 12th, 2021 AT 11:15 AM

12 Replies

Tiny
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  • 181 POSTS
Okay, after driving it a bit it does seem to be blowing warm air, but just barely. It appears to be split between the defrost and front facing vents, no matter what option I choose on the controls. Is there any way to fix the actuator or something?
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Friday, February 12th, 2021 AT 1:52 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,170 POSTS
Hi,

If you allow the engine to reach operating temperature with the heat on, do both the supply and return heater hose get hot? Can you upload a pic of the hose you are referring to that doesn't get hot? Also, are you sure the engine coolant is full?

Here is a link you may find helpful. Take a look through it and see if anything helps.

https://www.2carpros.com/articles/car-heater-not-working

Let me know if that helps or if you have other questions.

Take care and God Bless,

Joe
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Friday, February 12th, 2021 AT 3:53 PM
Tiny
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I added a second post that the heat does appear to work after driving for a bit but it blows out both the defrost and front vents at the same time. It’s like the damper it stuck open between them. Is there any way to fix that without disassembling the whole dash?
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Friday, February 12th, 2021 AT 4:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,170 POSTS
Hi,

That sounds like an issue with the mode door actuator. Because of the year, I don't have pics, but will try to help.

The actuator is run from the engine vacuum. If it isn't fully changing airflow direction, check under the dash for vacuum hoses. Make sure there are no broken, disconnected, or dry rotted hoses. With the engine running, you may hear a hissing sound which would indicate a leak.

Check it and let me know what you find.

Joe
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Friday, February 12th, 2021 AT 5:41 PM
Tiny
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Do you know if these vacuum lines would be far up inside the dash or down low where I could find them by removing the kick-plate?
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Saturday, February 13th, 2021 AT 4:43 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,170 POSTS
It has been some time since I've seen them, but you should be able to see them going to the heater box if you look under the dash. Actually, there should be a hose from the engine into the vehicle's HVAC control panel and distributed from that point.

Let me know if you find it or if you have other questions.

Take care,
Joe
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Saturday, February 13th, 2021 AT 6:44 PM
Tiny
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Default.
Okay, I managed to check inside the dash, all the vacuum lines look good there, no leaks.

But I am wondering if maybe I'm just not used to these older cars and how they operate the climate controls. I have noticed that if I set it to “vent” it will blow air from the front vents. If I set it to “defrost”, it will blow on the windshield. But if I set it to “heat”, it will blow only on the floor.

The A/C side seems to blow from the front vents only, unless I set it to bi-level then it will blow on the floor and front vents. But I have noticed the fan seems to blow stronger on A/C vs heat, not sure what that means, if anything.
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Tuesday, February 16th, 2021 AT 1:54 PM
Tiny
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  • MECHANIC
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Hi,

Based on how it's working for you, it sounds like it's correct. When you place it on heat, it should only come out on the floor level.

As far as the fan, if you place it on max ac, it will recirculate air and sounds louder. Is that what you experience?

Joe
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Tuesday, February 16th, 2021 AT 2:33 PM
Tiny
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Yeah, that’s it exactly. I guess I’m just used to these new-fangled cars where you can have it blow wherever you tell it to. Lol
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Tuesday, February 16th, 2021 AT 2:36 PM
Tiny
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Hi,

The newer ones allow you to split airflow in different directions. What you described is how this vehicle was designed.

I hope that helped. Please feel free to come back anytime in the future.

Take care and God Bless,

Joe
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Tuesday, February 16th, 2021 AT 6:14 PM
Tiny
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Small update: I think the control module might be a little wonky sometimes. I flip it to heat and stays on either the front facing vents or defrost (or both). At times it feels like it's coming from all the vents at once (floor, front, and defrost). Same thing with the A/C.

Sometimes if I move it to off then back over to heat it will rectify. It doesn't happen all the time, which makes me think it's the control module itself.
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Thursday, February 18th, 2021 AT 2:23 PM
Tiny
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Hi,

The change in direction is likely caused by low vacuum. Pay attention to if it happens more when climbing a hill or under acceleration. If that when it seems to happen, then check under the hood for vacuum leaks. There should be a vacuum hose that comes from the intake manifold and runs through the firewall into the vehicle

Let me know.

Joe.
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Thursday, February 18th, 2021 AT 6:03 PM

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