Pressures, Checking

- Before checking system pressures, check A/C system cooling performance. Evaluating 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 are 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). On Board Diagnostic, Air Conditioning 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/ recharging unit disconnected. 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. Carry out all A/C system pressure checks through the high pressure service valve.

Outside (ambient) Base pressure in refrigerant
temperature*) 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)

NOTE: 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 Hitec H1400A-TEL halogen leak detector (or equivalent) and 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 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 diagrams.
- 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).
- For switching pressure specifications of A/C refrigerant low pressure switch -F73- and A/C refrigerant high pressure switch -F118-