intermittent AC prolem

[r book]

Hello all, I'm a new member and need help with intermittent blower problem.
My AC works fine for about 20 to 30 minutes then it seems the duct gate slowly starts to close until I get no air from the vents even though the blower is working fine. Was wondering if this is a possible vacum problem.
I'm really stumped on this and my wife would really like to have her AC working. Thanks in advance for any help you can offer.
RBook

 

[Brock94]

It sounds like your evaporator is freezing up. There should be a temperature sensor that shuts off your compressor if the evaporator gets too cold-- that could be malfunctioning. If your evaporator gets below freezing, the condensation from the air will freeze onto it and block the airflow.

 

[r book]

follow up AC problem

Thanks for the reply Brock. I think you're right on target. Should have thought
of that myself. GuessI'll get a low pressure switch and see if that does it.
Thanks again, Randy

 

[BrooklynBay]

The pressure switch is made to cut out the compressor if you are low on freon. It is not temperature controlled. Did you check those small, cylinder shaped check valves that look like a black, and white disk with 2 small vacuum fittings?

 

[BrooklynBay]

Here is a picture of that check valve: