AC/heater and defrosters not blowing air out vents

Tiny
COOLOLDS85
  • MEMBER
  • 1989 BUICK REGAL
  • 2.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 55,900 MILES
A/C compressor and heater work and the blower motor turns on. But cannot feel any air coming out of vents with A/C and heat on. Defrosters do not even blow. Does anyone know if the A/C heater control ever go bad? Someone said vacuum lines, vacuum reservoir, HVAC lines or vacuum lines below brake booster could be old. Air is coming out from under the glove box, but not out of the vents. Anyone ever have this problem before?
Wednesday, May 16th, 2018 AT 2:16 PM

20 Replies

Tiny
KEN L
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Hello,

The first thing you must look for is to make sure the HVAC system is getting vacuum. Please inspect the vacuum lines from the engine to the firewall which feed the HVAC.

Here is a guide to help you see what I am talking about:

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

Please let us know what happens.

Cheers, Ken

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Friday, May 18th, 2018 AT 10:07 AM
Tiny
COOLOLDS85
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I checked all the vacuum lines and they seem to be okay. But my HVAC vacuum reservoir is not getting any vacuum and the vacuum line is not cracked or broken. I disconnected the line to see if any air would release and got nothing coming out.
I than reconnected the line to the canister and the inlet port broke off. Also, the defroster is not blowing much air out of the dash like it should to defog the windshields. When I use to press the control defroster button the air use to be full blast to defog the windshields. I am thinking the canister is the reason because no air is even coming out the instrument vents either.
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Friday, May 18th, 2018 AT 7:31 PM
Tiny
KEN L
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Yes, the system must have vacuum here is a diagram so you can see what happened (below).
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Saturday, May 19th, 2018 AT 9:11 AM
Tiny
COOLOLDS85
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All the vacuum lines are good under the hood. I just replaced some of the tubing on the egr harness. But the cruise control vacuum tank broke on me when I was disconnecting one of the vacuum lines to check if it still worked. Someone told me I would need to replace the Electric Vacuum Solenoid that works all the actuators. Would this fix my issue with getting no air out of the vents? Also would my defroster speed get stronger to clear the windshields?

Number 15 is what he told me to look at.
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Sunday, May 20th, 2018 AT 7:15 PM
Tiny
KEN L
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I remember a vacuum rotary valve on the rear of the control head that falls apart on these cars. Can you confirm you have vacuum at the control head?
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Monday, May 21st, 2018 AT 9:52 AM
Tiny
COOLOLDS85
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  • 173 POSTS
I do not think I do. I have a vacuum control solenoid that connects to the passenger side blend door. I think that is the bad part because it is not opening the door on the passenger side when the blower motor goes on to put air out of the vents.
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Monday, May 21st, 2018 AT 9:57 AM
Tiny
KEN L
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No vacuum to the control head is the issue. Find the broken line and it should be fixed.
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Monday, May 21st, 2018 AT 10:08 AM
Tiny
COOLOLDS85
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There is a vacuum line that connects to the control head? Are you referring to the A/C heater control module in the instrument panel?
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Monday, May 21st, 2018 AT 10:16 AM
Tiny
COOLOLDS85
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If no broken line at the control head could it be the control head it self? I heard they go bad sometimes.
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Monday, May 21st, 2018 AT 10:23 AM
Tiny
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I did check the lines and nothing broken near the control head. Only thing I found is the vacuum reservoir that broke. The line is not connected to that right now.
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Monday, May 21st, 2018 AT 12:34 PM
Tiny
KEN L
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I want to know if the control head is getting vacuum and the vacuum reservoir needs to work and be connected. Can you take a picture and upload it here so I can see what you are talking about with the reservoir?
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Tuesday, May 22nd, 2018 AT 9:46 AM
Tiny
COOLOLDS85
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The control head is getting vacuum and the vacuum reservoir is connected. I already replaced the vacuum reservoir anyhow because I cracked it by mistake where the vacuum line connects to on the vacuum reservoir. I also checked all actuators for vacuum between 15 psi to 25 psi. It holds good vacuum in all actuators like it should. I also checked the vacuum solenoid box and heater HVAC blend door actuator and the metal pintle still moves each direction when temperatures are adjusted on the control head. Everything I know of that holds vacuum still holds vacuum. The only place that I can feel air is blowing out is near the blower motor blend door and the evaporator core duct cover.
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Wednesday, June 6th, 2018 AT 4:28 PM
Tiny
KEN L
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Can you supply vacuum to each one of the blend door to see if there are any changes? It sounds like the door its self might have broken inside the heater plenum.
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Thursday, June 7th, 2018 AT 5:49 PM
Tiny
COOLOLDS85
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One thing I did notice was two of the HVAC vacuum panel mode actuators drop vacuum slowly when I was testing them. It is supposed to stay steady and it just begins to drop slowly. Also, the electronic HVAC blend door actuator barley moves and it connects to one of the doors. That actuator looks like it is connected to the passenger side blend door and it works the metal socket and spins each direction when cold/hot temperature is applied from the AC/heater controller.
The door should than open but it does not.
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Wednesday, June 13th, 2018 AT 9:51 AM
Tiny
KEN L
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Mode actuators will drop vacuum slowly which is normal. It sounds like the main controller is out. If you can move the door by hand and they seem to work and the unit has vacuum power and ground.
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Wednesday, June 13th, 2018 AT 2:50 PM
Tiny
COOLOLDS85
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If you are referring to the main controller on the instrument panel that is still working fine. I also tried replacing with a new one but did not fix anything. Please let me know what main controller you are referring to? I am thinking it is the actuator blend door that controls the temperature for AC and heat. Someone told me that had the same issue I am having when their vents are stuck in defrost mode. They said replacing the actuator blend door fixed the problem.
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Thursday, June 14th, 2018 AT 8:37 AM
Tiny
KEN L
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Yes, that could fix it. Here is another diagram I found for you.
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Thursday, June 14th, 2018 AT 10:09 AM
Tiny
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Ken, I had no luck with that part either. I am thinking it is something really serious now. I hope one of the doors is not broke. Because than does not that mean they have to remove the entire air duct door assembly?
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Friday, July 6th, 2018 AT 12:06 PM
Tiny
COOLOLDS85
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Ken with your experience of knowledge being in the automotive industry for so many years. What if my cars entire HVAC unit is bad? And if they do not make the unit because it is an older car. How much would it cost to replace the unit parts and labor? Is it in the ball park of what a house unit would cost? This is frightening me.
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Saturday, July 7th, 2018 AT 9:42 AM
Tiny
KEN L
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Do not get bummed yet, remove the blend door motors/actuators and move the doors by hand to see if they work. I have seen the blend doors break loose inside but it is rare. Also, while the actuators are off start the car and see if you can get them to move.
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Saturday, July 7th, 2018 AT 10:06 AM

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