Checking for Pressure

A/C Refrigerant System Pressures, Checking

Before checking refrigerant system pressures, Performance Checking

Test requirements
- Condenser and radiator clean and free of obstructions (clean if necessary)
- Expansion valve insulation properly installed and not damaged.
- Drive belts for compressor and generator in good condition and properly tensioned
- All air ducts, covers and seals OK and correctly installed
- Air flow through dust and pollen filter not obstructed by dirt
- Heating and A/C unit properly sealed (when fresh air blower is at maximum speed setting, no additional air is drawn in; air delivery is via vents only)
- Vehicle not standing in direct sunlight
- Outside (ambient) temperature more than 15 °C (59 °F).
- Engine at normal operating temperature
- All air distribution flaps reach end positions
- All instrument panel vents open
- Engine running and system set to maximum cooling (AUTO operating mode with LO temperature setting selected):
- A/C clutch -N25- engages compressor
- Coolant fan(s) -V7- run
- Fresh air blower -V2- running at maximum speed
- Fresh air/recirculated air flap moved to "recirculated air" setting (within 1 minute of starting the engine)
- Air should come out of the instrument panel vents
- Both temperature flaps in "cooling" position


NOTE: If any of the above test requirements is not obtained, check DTC memory and perform output Diagnostic Test Mode (DTM). Output Diagnostic Test Mode (DTM) (Function 03).


Preparation
- Check DTC memory and determine and repair all possible malfunctions Scan Tool Connecting and Initial Checks.

Checking pressures
- Switch ignition off.
- Connect refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, or equivalent..
- Read system pressures and compare temperature/pressure relationship with table:

Outside (ambient) temperature Refrigerant system pressure

+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)

If A/C refrigerant system 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(s) -V7- using wiring diagram.
- Check for pinched, kinked or damaged refrigerant lines/hoses.

If no problems are found:
- Discharge refrigerant system, flush with compressed air and nitrogen, evacuate and recharge.

If A/C refrigerant system pressure corresponds to or is higher than pressure specified on chart (vehicles with expansion valve and receiver drier):
- 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 Service and Repair.


- Raise engine speed to 2000 RPM.

Note high and low side pressures and compare with chart below.

Pressure specification chart (in bar)
A - High pressure
B - Low pressure
C - Allowable tolerance







- High side pressure may increase to, but not exceed 20 bar.
- Low side pressure may decrease to, but not exceed minimum value illustrated.

Determine high/low pressure relationship and refer to troubleshooting tables.


Troubleshooting tables