manifold pressure

Mathis · 07-28-2004, 06:34 PM

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.

Mercury · 07-30-2004, 12:47 AM

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.

Mathis · 07-30-2004, 07:31 PM

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

07-28-2004, 06:34 PM	#1
Mathis Registered Member Join Date: Jul 2004 Location: Winter Springs, Fl Posts: 4	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.

07-30-2004, 12:47 AM	#2
Mercury The Redneck James Bond Join Date: Sep 2000 Location: Fayetteville NC Posts: 1,707	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. __________________ 64 1/2 "D" code Red Mustang Coupe. Red Baron, 2000 Perf Red Mustang GT. 5spd. Stage 2 CNC heads with Large Valves, Comp Cams (270-274 dur .550 lift), Forged Crank, DRP pistons, Manly H-beams, Pro M 87 mm Mass Air, 24lb Inj, 75mm TB, Plenum Spacer ,Long Tube Headers, Homemade H-pipe, 2 chamber Flows, 4:10's, Steeda Tri-Ax, LKW 70/30's, Eibach Drag Springs, Steeda SubFrames, Battle Boxes, Rear Girdle, Adj uppers, Alunimum Drshft, Southside Lift Bars. Project Cars, 64 1/2 6cyl coupe, 1930 Model A Nostalgia Rod.

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07-30-2004, 07:31 PM	#3
Mathis Registered Member Join Date: Jul 2004 Location: Winter Springs, Fl Posts: 4	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