A/C Refrigerant System (R-134a), Checking Pressures

A/C refrigerant system (R-134a), checking pressures

Before checking refrigerant system pressures, check A/C system cooling performance. A/C System Cooling Performance, Testing

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 VAG1551 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 °C (59 ° - 113 °F)
- Engine running and system set to maximum cooling ("Auto" operating mode with "LO" temperature setting selected):
- Switch compressor ON (the warning light in the ECON button does not light up.
- Temperature selection "LO" (for driver and passenger side).

If the compressor is activated (A/C clutch is switched ON):
- Fresh air blower -V2- runs
- Coolant fan -V7- runs (at least in stage 1)
- Closes back pressure door and opens recirculation door (within 1 minute after starting vehicle)


NOTE:
- With open recirculation door air flows out of outlets in the instrument panel even though the back pressure door is closed.
- If the air comes out of the instrument panel outlets, left and right heat regulating valves -N175- and -N176- of pump unit are closed and coolant pump -V50- does not run (the heater cores are not warmed up).

If one of the requirements is not met, check DTC memory and repair any malfunctions.

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 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 actuation of coolant fan 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.

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.
- 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)

NOTE: For switching pressure specifications of A/C refrigerant low pressure switch -F73- and A/C refrigerant high pressure switch -F118-.

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

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