Head Pressure building up - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jeffro788 · 09-16-2010, 02:16 PM

Hey guys, we just put a serpentine set up on the truck, therefore we had to put the pancake style compressor on, I think it is what would go on an early 90's truck. I have dual electric fans (pullers) on the back of the radiator that are temperature controlled to kick on 190, and it still builds up head pressure. We tried to seal off the open area of the core support that is above the condenser (about a 4" gap), so the air would be pulled through the condensor. That didn't work...... Next we added a pusher fan on the front of the condenser that kicks on with the compressor only, along with with the dual pullers that kick on with the engine temperature. Still not working.... Not sure where to go from here, that 3" gap between the condensor and radiator is killing me..

Wrenchbender Ret · 09-16-2010, 04:40 PM

If you are using 134A it doesn't take as much coolant as R12 & naturally has more high side pressure. You may have too much in it. There is a special low pressure switch available for changeover. In real hot weather the high side pressure is going to be very high.

**DANTIP** · 09-16-2010, 09:12 PM

Over-charging is a possibility. Extra system charge effectively reduces your condenser's capacity. Also air in your system will end up in the condenser and will increase your discharge/head pressure. Was the system properly evacuated prior to charging?

jeffro788 · 09-17-2010, 11:37 AM

We are running r134 right now, but I think we are going to change over to freeze12. I really don't know a whole lot about a/c, so we had a local shop do the leak testing and charging. We did do the retro fit, I think that is the expansion valve that has the pressure switch on it. I do know that when you turn on that compressor you can really feel a "bump" in the engine right when you turn it on. I figured this can't be to hard since it came from the factory with this condensor set up, although it had a mechanical fan and not 3 electric fans.

dwcsr · 09-17-2010, 11:52 AM

Wire your fans to come on when the compressor comes on and the head pressure should drop. Head pressue will rise without propper air flow over the coil.

09-16-2010, 02:16 PM	#1
jeffro788 Registered User Join Date: May 2009 Location: Little Rock, AR Posts: 71	Head Pressure building up Hey guys, we just put a serpentine set up on the truck, therefore we had to put the pancake style compressor on, I think it is what would go on an early 90's truck. I have dual electric fans (pullers) on the back of the radiator that are temperature controlled to kick on 190, and it still builds up head pressure. We tried to seal off the open area of the core support that is above the condenser (about a 4" gap), so the air would be pulled through the condensor. That didn't work...... Next we added a pusher fan on the front of the condenser that kicks on with the compressor only, along with with the dual pullers that kick on with the engine temperature. Still not working.... Not sure where to go from here, that 3" gap between the condensor and radiator is killing me.. __________________ 1972 Chevy SWB - ZZ4 crate motor, 700r4, makes lots of noise! - SOLD 1987 Chevy SWB - SOLD 2000 Chevy SWB - 6.0L heads, Lunati cam, Whipple supercharger, 3.73 posi, caltrac traction bars, headers, custom tune and Borla race muffler. 500 H.P. 1970 Oldsmobile Cutlass 442 w-30 - original

09-16-2010, 04:40 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,228	Re: Head Pressure building up If you are using 134A it doesn't take as much coolant as R12 & naturally has more high side pressure. You may have too much in it. There is a special low pressure switch available for changeover. In real hot weather the high side pressure is going to be very high.

09-16-2010, 09:12 PM	#3
DANTIP Registered User Join Date: Sep 2001 Location: Fort Wayne, Indiana, USA Posts: 1,889	Re: Head Pressure building up Over-charging is a possibility. Extra system charge effectively reduces your condenser's capacity. Also air in your system will end up in the condenser and will increase your discharge/head pressure. Was the system properly evacuated prior to charging?

09-17-2010, 11:37 AM	#4
jeffro788 Registered User Join Date: May 2009 Location: Little Rock, AR Posts: 71	Re: Head Pressure building up We are running r134 right now, but I think we are going to change over to freeze12. I really don't know a whole lot about a/c, so we had a local shop do the leak testing and charging. We did do the retro fit, I think that is the expansion valve that has the pressure switch on it. I do know that when you turn on that compressor you can really feel a "bump" in the engine right when you turn it on. I figured this can't be to hard since it came from the factory with this condensor set up, although it had a mechanical fan and not 3 electric fans. __________________ 1972 Chevy SWB - ZZ4 crate motor, 700r4, makes lots of noise! - SOLD 1987 Chevy SWB - SOLD 2000 Chevy SWB - 6.0L heads, Lunati cam, Whipple supercharger, 3.73 posi, caltrac traction bars, headers, custom tune and Borla race muffler. 500 H.P. 1970 Oldsmobile Cutlass 442 w-30 - original

09-17-2010, 11:52 AM	#5
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,134	Re: Head Pressure building up Wire your fans to come on when the compressor comes on and the head pressure should drop. Head pressue will rise without propper air flow over the coil.

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