General Motors Retrofit Procedures

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Special Notes:
Recommendations From A/C Shops:
Any head pressure over 250 PSI will hamper cooling and any head pressure over 325 PSI should be considered overheating.
Adjust the low limit of the clutch cycling switch to 21 PSI.
On 1988 to 1992 Cadillacs, replace the low temperature sensor. This is to alleviate a false reading of codes 46 & 47 (low inlet temperature).
On all vehicles you should:
MINERAL OIL REMOVAL
None Recommended GM states that the normal charge of mineral oil left in the A/C system after retrofit with R134a will not harm system operation. There test indicate that mineral oil does not mix with R134a, and will park in places such as the accumulator and evaporator. GM further states that mineral oil and PAG oil are chemically compatible. After all this is said GM warns that overcharging may lead to pushing the mineral oil through the system leading to loss of performance and possible compressor failure. I recommend removing as much oil as possible!
FLUSHING THE SYSTEM
Flushing of the A/C system is not recommended or approved by GM. GM recommends the use of in-line filters as an alternative to flushing. GM states that any residual flushing solvent left in an A/C system may be very damaging and that it may also be incompatible with R134a. I recommend flushing, see general retrofit procedures.
O-RINGS & GASKETS
All o-rings and gaskets replaced should be R134a compatible. I cover o-rings and gaskets with mineral oil.
HOSE REPLACEMENT
GM does not recommend the replacement of hoses unless they show signs of leaking.
COMPRESSOR
GM states that the compressor is not part of the normal retrofit, unless indicated by their compressor replacement chart.
I have heard of some problems when retroffiting the GM V5 compressor. The GM V5 is a variable displacement compressor. It changes its displacement by changing the length of the pistons stroke. It does this by changing the angle of the swash plate that moves the pistons back and forth. There is a refrigerant control valve that controls the swash plate in relation to the pressure and temperature of the refrigerant. R-12 and R-135a have a slightly diferent Pressure Temperature relationship. If you retrofit a system with a GM V5 make sure you flush. Four Seasons has a V5 control valve for for R-134a use (Four Seasons PN 38846). GM states that the V5 compressor should be used with special non foaming oil GM PN . Four Seasons recommends their PAG oil PN 59003 for use with their remanufacture V5 compressor. When you do change a compressor, make sure you know what type oil it contains.
CONDENSER AND AIR FLOW (HEAT EXCHANGE)
GM does not make recommendations of condenser replacement. I see problems and needs in this area, see general retrofit procedures. When you do change a condenser try to use a multiflow model. General Motors recommends an auxiliary condenser fan for some models PN 22134515, with a fan mountin kit PN 10254709, a HPCO (high Pressure cut Out) switch PN 15981985 and a saddle clamp to mount it on PN 15985307.
FILTER DRIER / ACCUMULATOR REPLACEMENT
GM states that change is not mandatory or covered under warranty. They state that their test show, old driers used with R-12 are sutable for use with R-134a. This policy may be to keep them from spending money when the retrofit is done under warranty. Driers/accumulators over 5 years old should be replaced with the retrofit. When replacement is done, use driers/accumulators with XH-7 or XH-9 desiccant. 1993 and newer GM vehices have driers/accumulators with the new desiccant material.
EXPANSION VALVE
The expansion valve is not part of the normal retrofit. Some shops I have talked to install new expansion valves when they retrofit a dual evaporator systems.
EVAPORATOR
The evaporator is not part of the normal retrofit.
Suction Control Valves For Non-Cycling Compressors
General Motors has used various control valves, the STV (Suction Throttling Valve), the POA (Pilot Operated Absolute) valve, and the V5 compressor control Valve. They control and cycle the minimum pressure in the evaporator, there by controlling and cycling the minimum temperature. The aftermarket states that you should be adjusted back 3 to 4 PSI with R-134a in order to achieve the same temperature. This is because the pressure temperature relationship of R-12 and R-134a is different. For instance at 25 F the pressure of R-12 is 24.6 PSI and the pressure of R-134a is 22.1 PSI.
Pressure Temperature Table
Most valves will have a lock nut and an adjustment screw on the inlet end. One eight turn counterclockwise lowers the low side pressure approximately 2 PSI and one quarter lowers the low side pressure approximately 4 PSI. I have not heard of any mention of the V5 compressor control valve, which changes the compressor displacement acording to temperature.
CLUTCH CYCLING SWITCH
Recommendations From A/C Shops and Aftermarket:
Lower the adjustment of the clutch cycling switch to 21 to 22 PSI. This is because the pressure temperature relationship of R-12 and R-134a is different. For instance at 25 F the pressure of R-12 is 24.6 PSI and the pressure of R-134a is 22.1 PSI.
Pressure Temperature Table
If it is adjustable there will be an adjustment screw between the two terminals. One eight turn counterclockwise lowers the cut out pressure approximately 2 PSI and one quarter lowers the cut out pressure approximately 4 PSI.
HIGH PRESSURE RELIEF VALVE (HPRV)
No recommendations.
HIGH PRESSURE CUTOUT (HPCO) SWITCH
GM states that most trucks and some 1984-93 B nad D cars require that HPCO switch should be installed.
GM Car Model Body Styles
GM supplies various saddle clamp ports to add the HPCO switch. The HPCO switch is Gm PN (15981985), Delco PN (15-5514) and a saddle clamp to mount it on PN 15985307. I think a high pressure cut out switch is a worth while safeguard. A trinary witch could be added and function as a LPCO a HPCO and as a condenser fan switch.
OTHER PARTS
No recommendations.
OIL REPLACEMENT
GM recommends you refill the system with a full charge of the proper PAG oil. I recommend that you use Ester oil if you flush.
SERVICE PORT ADAPTERS
Special R134a only service ports that meet SAE requirements are required by law. Leave the valve core in straight service port adapters fittings and remove the valve core when using 90 degree adapters fittings.
REFRIGERANT REPLACEMENT FOR R12
R134a as the only substitute for R12 refrigerant that GM recommends. Recharge the system with about 15% less R134a than the R12 specification. Their formula is: (R12 lbs x .9) - .25 lb. = R134a Charge
LABELS
Special R134a service labels that meet SAE requirements are required by law.

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