A/C Refrigerant System, Checking Pressures

A/C Refrigerant System, Checking Pressures

Safety measures
Before checking refrigerant system pressures, check A/C system cooling performance.
Use high pressure service valve for checking system pressures.

Test requirements
- 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 DTC memory using V.A.G 1551 scan tool and eliminate/repair any malfunctions indicated (not affecting 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
- Outside (ambient) temperature must be between 15-45 degrees C (59-113 degrees F)
- Engine running and system set to maximum cooling (AUTO operating mode with LO temperature setting selected):
- Switch compressor on (warning light in ECON button does not light up)
- Temperature selection LO (for driver and passenger side)

If the compressor is activated (A/C compressor is switched on):
- Fresh air blower -V2- runs
- Coolant fan -V7- runs (at least in 1st speed)
- Air flow flap closes and fresh air/recirculated air flap opens (within 1 minute after starting vehicle)

NOTE: With fresh air/recirculated air flap open air flows out of outlets in the instrument panel even though the air flow flap is closed.

Preparation work
- Check DTC memory and determine and repair all possible malfunctions.

Checking
- Switch ignition off.
- Connect high pressure hose of refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, or equivalent, to high pressure service connection.
- Leave low pressure hose of refrigerant recovery/recycling/recharging unit disconnected.

NOTE: Only the high pressure service valve is used for A/C system servicing. Perform all A/C system service operations (i.e. discharging, evacuating and charging) through the high pressure service valve only.

Outside (ambient) Base pressure in
temperature 1) refrigerant system
(engine OFF)
+15 degrees C (59 degrees F) 3.9 bar (56.5 psi)
+20 degrees C (68 degrees F) 4.7 bar (68.2 psi)
+25 degrees C (77 degrees F) 5.6 bar (81.2 psi)
+30 degrees C (86 degrees F) 6.7 bar (97.2 psi)
+35 degrees C (95 degrees F) 7.8 bar (113.1 psi)
+40 degrees C (104 degrees F) 9.1 bar (132.0 psi)
+45 degrees C (113 degrees 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 actuation of coolant fan -V7- according to wiring diagram.
- Check for pinched, kinked or damaged refrigerant lines/hoses.

If no problems are found:
- Discharge refrigerant 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.

Compressor runs continuously.
- Raise engine speed to 2000 RPM.
- Note pressure on A/C high pressure gauge.

Specified high pressure value: high side (discharge) pressure increases from base pressure (engine OFF) to maximum 20 bar (290 psi).

Pressure in A/C system corresponds to chart or is higher:
- Start engine.
- Adjust A/C to maximum cooling performance.

NOTE: If compressor is not activated, note test requirements.