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I would be inclined to think that you have a vacuum leak that is causing the blend doors to move when you go WOT and lose manifold vacuum.

If your AC is hooked up on switched power and relays with line pressure switches (i.e. totally isolated from the engine) then it has no way of knowing when you go WOT and shutting off the compressor.



The HVAC system on these cars has no connection what so ever to the engine besides the vacuum on the blend doors. The only way the compressor can shut off (in A/C mode) is with a low pressure situation from the drier sensor which will break the clutch circuit if the pressure drops to save the compressor from damage.

Replace the check valve on the vacuum harness. They have them in the HELP section at Advance Auto and similar chain stores. The next thing would be the vacuum servos themselves which could have a slightly torn diaphragm causing it to leak down prematurely and close the bend doors the moment vacuum drops.

You can also test this theory if you pump the brakes (if power) repeatedly and listen/feel for the doors to close while the A/C is on. This will have a similar effect to WOT on the vacuum.

Good luck but don't overthink this!