Pressures, Checking

- Before 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 and eliminate/repair any malfunctions 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 - 113 °F (15 - 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/re- charging 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.


Outside (ambient) Base pressure in refrigerant
temperature1) system (engine OFF)
+15 °C ( 59 °F) 3.9 bar ( 56.5 psi)
+20 °C ( 68 °F) 4.7 bar ( 68.2 psi)
+25 °C ( 77 °F) 5.6 bar ( 81.2 psi)
+30 °C ( 86 °F) 6.7 bar ( 97.2 psi)
+35 °C ( 95 °F) 7.8 bar (113.1 psi)
+40 °C (104 °F) 9.1 bar (132.0 psi)
+45 °C (113 °F) 10.5 bar (152.3 psi)

1) 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.
A/C compressor clutch engages and compressor is driven


NOTE:
- If A/C clutch -N25- 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.
- Make note of 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 -F73- and A/C refrigerant high pressure switch -F118-