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Potential heater and AC control assembly problem

argentum50 on Fri July 03, 2009 1:26 AM User is offline

Year: 1997
Make: Chevrolet
Model: Lumina
Engine Size: 3.1L
Refrigerant Type: R134a
Country of Origin: United States

I have just finished repairing the ac system in my 1997 chev lumina sedan 3.1L, and everything seemed to be working fine until I started to drive the car. The system had been thoroughly flushed, and both a new evaporator and accumulator were installed. What happens is when the blower is set to the highest setting, hardly any air comes out of the dash registers (the air is cold, though). In fact, most of the air is felt blowing out of the heater core/evaporator cover assembly just above my legs . . . and the air coming from there is luke warm (definitely not cold).

Another interesting phenomenon happens when I accelerate the car. When I accelerate, the air stops flowing through the dash registers completely until I have reached a constant velocity.

So, I have poor flow through the dash registers when operating the car and I get no flow through the dash registers when I accelerate. Can somebody please tell me what is going on? How can I fix this? Would the problem lie in the heater and ac control assembly? Thanks.

mk378 on Mon July 06, 2009 2:31 PM User is offline

Sounds like the controls are operated at least partly by engine vacuum. These systems have a check valve and reservoir under the hood so it doesn't lose vacuum inside when accelerating heavily (during which time the vacuum at the manifold drops). The check valve could be leaking backwards or there could be a leak somewhere allowing the vacuum to go away, and then the air doors close.

knightgang on Tue July 21, 2009 8:55 PM User is offline

I have a 1997 Olds Cutlass that had the issue of airflow switching from vent to floor/defrost on acceleration and it turned out to be a vacuum line broken under the hood. Mine was located under the car (more or less) just in fromt of the front left side tire. Find that vacuum resevoir and trace the vacuum line, you will probably find a break.

As for the airflow poor airflow to begin with, have you checked the in cabin air filters on the system. Just a thought...

GM Tech on Tue July 21, 2009 10:26 PM User is offline

Another "W" car scenario-- just had the same posting 2 days ago -- broken black plastic vacuum line- under battery tray.....

Another W-car vacuum leak

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Wed July 22, 2009 at 8:41 AM by GM Tech

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