System Pressures, Checking
A/C REFRIGERANT SYSTEM (R-134A) PRESSURES; CHECKINGBefore checking system pressures1 check A/C system cooling performance, see page 87-130-1 (Manual A/C) or page 87-180-1 (Auto. climate control.)
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 or A/C and recirculation buttons pressed and temperature setting on full cold),
- 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.
* All components of A/C system must be at the specified temperature for an accurate pressure measurement.
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
^ NO compressor clutch engages and compressor is driven
Note!
If A/C clutch is not engaged1 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 and A/C refrigerant high pressure switch