The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - AC high pressure cut out switch needed or not?

**hatzie** · 06-08-2013, 09:21 AM

Alabama qualifies as a HOT climate New England does not. R134 runs higher pressures than hydrocarbon blend or R12 refrigerants. The R134 system on my 2000 GMC C2500 T400 chassis has a high pressure cutoff switch. If GM decided it was necessary on the factory R134 system it should be installed on a retrofit.

On my 2000 GMC 2500 T400 chassis the switch on the accumulator is the LPCO and the switch on the compressor is the HPCO. I mimicked that setup on the '98 6.5L with its' H series compressor that I installed in my '76. I put in a parallel flow condenser, variable orifice valve and late 80's accumulator/evaporator. I have yet to see high pressure cutout... but #1 I was extremely careful about charging using gauges and thermometers not assuming using pounds of refrigerant. #2 I was in Cincinnati and am now in Northern New England so summer isn't as rough as the Deep South. On the 76 My high side pressure is reasonable at 90°F ambient temp and My vent temps are 40-45°F.

Make sure the HPCO is on the high side and LPCO is on the low side.

06-08-2013, 09:21 AM	#20
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,021	Re: AC high pressure cut out switch needed or not? Alabama qualifies as a HOT climate New England does not. R134 runs higher pressures than hydrocarbon blend or R12 refrigerants. The R134 system on my 2000 GMC C2500 T400 chassis has a high pressure cutoff switch. If GM decided it was necessary on the factory R134 system it should be installed on a retrofit. On my 2000 GMC 2500 T400 chassis the switch on the accumulator is the LPCO and the switch on the compressor is the HPCO. I mimicked that setup on the '98 6.5L with its' H series compressor that I installed in my '76. I put in a parallel flow condenser, variable orifice valve and late 80's accumulator/evaporator. I have yet to see high pressure cutout... but #1 I was extremely careful about charging using gauges and thermometers not assuming using pounds of refrigerant. #2 I was in Cincinnati and am now in Northern New England so summer isn't as rough as the Deep South. On the 76 My high side pressure is reasonable at 90°F ambient temp and My vent temps are 40-45°F. Make sure the HPCO is on the high side and LPCO is on the low side. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful. Last edited by hatzie; 06-08-2013 at 09:50 AM.