What started as an inconvience has become an issue. The a/c would stop blowing when accelerating under load as going up hill. Has become no cold air from the dash vents at all. It does come out of the defrost vents. Is there an easy solution?
What year and model? Generally this is from a failing vacuum check valve that is near the intake manifold or brake booster and goes into the dash. When manifold vacuum drops under load, the valve keeps good vacuum in the HVAC control lines for holding the selected mode. It will always default to defrost for safety if the vacuum drops.
It should be pictured on your underhood vacuum map.
There is a re-designed vacuum check valve that prevents this. Look on your power brake booster for a small, disk-shaped plastic device that has a thin vacuum hose attached to it. The re-designed check valve is shaped and sized more like a 35mm film canister (if you know what that is). It simply pulls out for replacement.
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