A/c 87 cutlass
- Thread starter Herbert hunter
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The vent mode switch and actuators are vacuum operated. Usually when the mode won't switch from defrost the system isn't getting any vacuum or is leaking vacuum. With the engine running can you hear a hissing sound inside the car or under the hood near the blower motor? Run the engine for a minute and then turn the engine off. Immediately change the mode selection say from defrost to normall. Do you hear anything? A slight hiss or the sound of movement under the dash?
x2 likely a vacuum leak. The system defaults to defrost when there is no vacuum present. Did you always have this problem or did it start recently?
In addition to listening for leaks at the controller in the dash I would also check for leaks under the hood. AC Cars got a black plastic ball mounted conveniently above the exhaust manifold on the passenger side ( which in my case has melted twice before I moved it to the inner fender ). This ball will keep the system under pressure when the engine comes under load and vacuum drops ). The plastic lines run off the intake to the ball and from the ball into the car as the vacuum source. Beware they become brittle and crack easily with age so don't be tugging on them too hard.
In addition to listening for leaks at the controller in the dash I would also check for leaks under the hood. AC Cars got a black plastic ball mounted conveniently above the exhaust manifold on the passenger side ( which in my case has melted twice before I moved it to the inner fender ). This ball will keep the system under pressure when the engine comes under load and vacuum drops ). The plastic lines run off the intake to the ball and from the ball into the car as the vacuum source. Beware they become brittle and crack easily with age so don't be tugging on them too hard.
That one should be for the cruise control. You should have another on the other side of the engine compartment, near the A/C accumulator (silver tank).
Does this problem occur in all the A/C positions (Max, Norm, Bi-level)? The other day when I was using my A/C, in the Max position, the air came out the defroster vents, but out the dash registers in Norm. I haven't looked into it yet. Might be an adjustment is needed.
Are these little silver tanks suppose to have any air in them like when u take off the little black caps an push the valve
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