Porsche P-80 2005, Manual

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Page 1.10
Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Mechanical Regulating Valve
Porsche Sports Cars use variable displacement compres-
sors with mechanical regulating valves. Cayenne models
have a variable displacement compressor controlled by a
PWM electronic control valve. Both types regulate
compressor displacement by changing pressure in the
crankcase under the pistons.
Pressure Relief Valve
Porsche A/C compressors have a spring loaded mechan-
ical pressure relief valve. If system pressures get danger-
ously high, the valve will open and vent the excess
pressure. The valve closes when pressures have dropped
to safe levels to prevent the complete loss of refrigerant.
Opening pressure is approximately 38 bar (550 psi). The
valve will close when pressures have dropped to approxi-
mately 30-35 bar (435-508 psi). Removal of the pressure
relief valve first requires recovery of the refrigerant from
the system.
Lubrication
All A/C compressors requires oil for lubrication. The oil
reduces internal friction and heat and helps to seal moving
parts. This lubricant is carried by the flow of refrigerant
throughout the system and it must be compatible with the
refrigerant, seals and components.
Porsche A/C systems with R-134a refrigerant use
synthetic PAG (polyalkylene glycol) or ester oil. R-12
systems use mineral oil. These oils are not compatible.
Mineral oil will not mix with R-134a refrigerant and must
not be used in R-134a systems. Since the oil flows with
the refrigerant throughout the system, a portion of the
total oil charge must be replaced when any component is
replaced. Some oil may also be removed along with the
refrigerant when discharging a system.
A/C service stations have provisions for capturing and
measuring any oil removed so that an equal amount can
be restored. A typical system contains approx. 195 cm3
(6.6 oz.) of ND8 PAG oil. Refer to Service Information for
specifications regarding the amount of oil to add for each
system component.
Caution:
• Always store refrigerant oil in closed containers. These
oils are very hygroscopic, that is, they readily absorb
moisture.
• Never reuse refrigerant oil from a system. Always
replace with fresh uncontaminated oil.
• Always consult the Repair Information for the correct oil
specification and quantity.