manifold pressure
 

I have a 2000 GT. On hard acceleration ( not full throttle) the a/c was changing from max air to defrost. I checked the manifold pressure and found it at 15 inches mercury at idle ( also saw that with no vacuum to the A/C control the system defaults to defrost.

15 inches seems very low. I checked for loose hoses and didn't find any. Since I have an extended warranty and the emmisssions warrantuy is still in affect I took it to the dealer ( also the transmission would not up shift to third till you let up on the gas).

Dealer says the transmission has a broken spring in the 2-3 accumulator.

But also says the 15 inches vacuum is normal for this car. The A/C guy is tearing everything apart.

I think the vacuum should be above 17 inches. I live in FL so hardly any elevation above seal level. The car is stock.

Caan some one confirm what the expected manifold vacuum should be.

Dont forget that mileage and wear on an engine will affect Engine Vacum.

How many miles you got? 15in of Vacum is about right.

Strange, but I never even thought if Mustangs have a WOT Air conditioner switch. I never noticed on mine, then again, I dont run the AC much at all...maybe 20 times since I've had the car, and I bought it new in 2000.

45000.

They changed the a/c switch and check valve. It acts normal now. I have not rechecked the manifold pressure since I got it back. There is a wide open throttle switch which cuts out the compressor