92, buick lasabre a/c problem


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Old 08-06-06, 01:53 PM
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92, buick lasabre a/c problem

I have a 92' buick lasabre, the a/c blows cold air. Every few minutes though the a/c will go from front vents to the defrost vents, blowing cold for both of them. It will keep this cycle up all day long. Mean while you are roasting everytime it goes to the defrost vents. How can I stop this and what is the problem. I appreciate any words of wisdom.
 
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Old 08-06-06, 02:19 PM
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I'd say you have a vacuum leak for your control. Does this shifting between the vents happen at idle, or cruising?,... or does this shifting happen more when your car changes between load requirements, like when going up hills, coming to a stop...or from any change?

I had this problem in my 91 Spirit and found that the small vacuum tube that forks off of the brake booster was torn. Everytime I went up a hill or otherwise applied more throttle, the panel venting would shift to defrost venting. I fixed the tube and solved my problem.
 
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Old 08-07-06, 04:13 PM
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I am not sure, I will check to see if I have any vac leaks. Thanks for the tid bit.
 
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Old 08-08-06, 01:12 PM
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That thing is a check valve to momentarily hold vaccum to the air doors for when you press on the gas and vacuum disappears. For safety reasons, defrost mode is the design's default mode for when vacuum disappears.
 
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Old 08-08-06, 10:33 PM
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So, what you are saying is, You agree that there is a vaccum leak. Right, I still have not had a chance to check that theory out yet (due to illness and a job) but as soon as I get a chance to check, I will post it.
 
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Old 08-09-06, 05:09 AM
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Yes, there is a vacuum leak, but not to the outside. The leak is within the check valve. The check valve is essentially a one-way valve for air movement.
 
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Old 08-09-06, 03:32 PM
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where is the check valve located?
 
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Old 08-09-06, 04:46 PM
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BTW, you could also have a bad vacuum tank.

To answer your question though, the vacuum check valve is found behind the instrument panel on the engine vacuum source line (violet in color). You could also have a vacuum leak outside under the hood as obviously the vacuum source is the engine. This is also the most likeliest place to have a vacuum leak I have found. I would check under the hood...you should see where the violet line comes out of the firewall somewhere back behind the engine. Trace it to its source on the engine and make sure there are no leaks under the hood first.
 
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Old 08-10-06, 07:47 AM
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Thanks I'll look into that.
 
 

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