I have a 1993 GMC safari van. When I accelerate on the highway the air slows or completely stops flowing from the ac vents. When I let off the gas and slow down it resumes the normal air flow. Does anyone know how to fix this?
Since no one has answered this- I'll get you started on a possible fix. My A/C system has dampers that default to Defrost Mode when they lose vacuum. This is so you can still see the road when you have a vacuum problem. Next, there are check valves in the vacuum system. I have even less knowledge of this but I believe the vacuum is proportional to engine RPM. When you accelerate, the vacuum controlling your A/C dampers is greater. Given that your system is 20 years old, I suspect you have a check valve leaking (or another leak) that opposes the selected damper position when you accelerate, causing the damper to go to default position and then back as the vacuum is reduced. You can get some quick diagrams on Ebay if you search for parts like 'expansion valve'. Just a thought...
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