A/C Refrigerant System Pressures, Checking
A/C Refrigerant System Pressures, Checking
- Safety measures.
- Before checking refrigerant system pressures, check A/C system cooling performance. A/C Cooling Performance, Testing
- Service connections.
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 degrees C (59 degrees 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 Check DTC Memory (Function 02) and perform output Diagnostic Test Mode (DTM).
Preparation
- Check DTC memory and determine and repair all possible malfunctions. Check DTC Memory (Function 02)
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:
- If specified values are not obtained.
- 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
- 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
NOTE: If system performance does not meet specifications after evacuating and recharging system, flush system with compressed air and nitrogen.
NOTE: If system performance does not meet specifications after flushing with compressed air and nitrogen, evacuating and recharging system, replace expansion valve.
NOTE: Always replace receiver drier when refrigerant system has been left discharged with open components.
NOTE: If system performance does not meet specifications after repeating test, re-install original expansion valve, flush system with compressed air and nitrogen and replace compressor.
NOTE:
- If system performance does not meet specifications after repeating test, re-install original expansion valve, flush system with compressed air and nitrogen and replace compressor.
- In cases with "low pressure too low", and the refrigerant fill quantity is found to be OK, check for evaporator icing.
NOTE: In the above cases, a malfunctioning compressor may have been replaced without having compensated for the amount of refrigerant remaining in the system (replacement compressor was not drained accordingly).