System Pressures and Checking
A/C REFRIGERANT SYSTEM (R-134A) PRESSURES, CHECKINGBefore checking system pressures, check A/C system cooling performance
Use A/C system high pressure service valve for checking A/C system pressure.
TEST CONDITIONS
^ condenser and radiator clean and free of obstructions (clean if necessary)
^ drive belts for compressor and Generator in good condition and properly tensioned
^ all air ducts, covers and seals OK and correctly installed
^ check On Board Diagnostic (OBD) Diagnostic Trouble Code (DTC) memory using VAG 1551 Scan Tool (ST) and eliminate/repair any malfunctions (DTC's) indicated (not affecting the A/C system)
^ all air distribution flaps reach end positions
^ engine at normal operating temperature
^ evaporator housing and heater box do not leak air (draw in secondary air) at high fresh air blower speed
^ with engine running, and system set to maximum cooling ("Auto" operating mode with "LO" temperature setting selected and recirculation button pressed),
- fresh air blower runs
- coolant fan runs
- fresh air/recirculating air flap in "recirculating air" position
- temperature flap in "cooling position"
^ outside (ambient) temperature must be between 59°F - 113°F (15 C - 45 C)
Checking
- switch ignition OFF
- connect high pressure hose of refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, or equivalent, to high pressure service valve
- leave low pressure hose of refrigerant recovery/recycling/recharging unit disconnected
Note
Only a high pressure service valve is used for A/C system servicing and checking pressures. A low pressure service valve is not installed in the A/C system. Perform all A/C system pressure checks through the high pressure service valve.
If A/C refrigerant system base pressure is less than specified on chart, system is low on refrigerant.
- check system for leaks using halogen leak detector Hitec HI400A-TEL or equivalent, repair system as necessary
- check pressure relief valve on A/C compressor
If the pressure relief valve has blown,
- check triggering of coolant fan according to wiring diagram
- check for pinched, kinked or damaged refrigerant lines/hoses
If no problems are found
- discharge A/C system, then evacuate and recharge
If A/C refrigerant system pressure corresponds to or is higher than base pressure specified on chart,
- start engine
- adjust A/C to maximum cooling
^ A/C compressor clutch engages and compressor is driven
Note
If A/C clutch (N 25) is not engaged, check voltage supply to A/C clutch according to wiring diagram. If voltage is OK, repair (replace) A/C clutch.
- raise Engine Speed (RPM) to 2000
- Note pressure on A/C high pressure gauge
Specified pressure values
^ high side (discharge) pressure increases from base pressure (engine OFF) to maximum 20 bar (290 psi)
Note
For switching pressure specifications of A/C refrigerant low pressure switch (F 73) and A/C refrigerant high pressure switch (F 118).