A/C Refrigerant System Pressures, Checking
A/C Refrigerant System Pressures, Checking
Check A/C refrigerant system pressures using these tests:
1 - A/C system cooling performance
2 - Refrigerant system high side pressure test
3 - Refrigerant system low side pressure test
The combined results of these tests determines which part of the A/C system requires further troubleshooting and/or repairs.
Test conditions
- A/C refrigerant system fully charged; discharge, evacuate and recharge system if necessary
- Condenser and radiator clean and free of obstructions (spray clean if necessary)
- Air distribution can be adjusted correctly using control knobs (all air distribution flaps reach end positions)
- Wiring OK per wiring diagram
- No Diagnostic Trouble Codes (DTCs) and no A/C compressor shut-off conditions stored/visible in the Climatronic On Board Diagnostic system. Check with VAS 5051/5052 tester in operating mode "Guided Fault Finding".
- Outside (ambient) air temperature between 20-30 degrees C (68-86 degrees F)
- Vehicle is not parked in direct sunlight
- Engine at operating temperature.
- Drive belts for A/C compressor and Generator in good condition and properly tensioned
Test 1: A/C system cooling performance
- Start engine.
- Set temperature control to maximum cooling (LO").
- Adjust air distribution to instrument panel outlets.
- Insert thermometer into center instrument panel outlet
- Raise engine speed to approximately 2000 RPM.
Specified result
With humidity normal and outside (ambient) temperature between 20-25 degrees C (68-77 degrees F), system is cooling satisfactorily if air temperature from center instrument panel vent drops below 10 degrees C (50 degrees F) within 1 minute.
For higher ambient temperatures and/or higher humidity, specified air temperature from center instrument panel vent can be slightly higher.
If specified reading is not obtained, perform tests 2 and 3, then compare results of all three tests.
Test 2: A/C system high pressure, checking
- Connect high- and low-pressure hoses of refrigerant recovery/ recycling/recharging unit Kent-Moore ACR4 (or UL approved equivalent), to high- and low-pressure service valves.
- Start engine.
- Set temperature control to maximum cooling ("LO").
- Adjust air distribution to instrument panel outlets.
- Raise engine speed to approximately 2000 RPM.
Specified result
System high pressure rises from starting pressure to 20 bar (290 psi).
For higher ambient temperatures and/or higher humidity, specified pressure can rise to a maximum of 29 bar (420 psi).
If specified reading is not obtained, also perform test 3 and compare results of all three tests.
Test 3: A/C system low pressure, checking
- Connect high- and low-pressure hoses of refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, (or UL approved equivalent), to high- and low-pressure service valves.
- Start engine.
- Set temperature control to maximum cooling ("LO").
- Adjust air distribution to instrument panel outlets.
- Raise engine speed to approximately 2000 RPM.
Specified result
System low pressure falls from starting pressure to pressure indicated
A - Low pressure in bar
B - Actuating voltage for compressor regulating valve -N280-
C - Permissible tolerance
NOTE:
- Actuating voltage for -N280- is visible from Read Measuring Value Block.
- The low pressure adjusts automatically within the tolerance range within the output of the compressor depending on the actuating voltage for -N280-.
- For higher ambient temperatures and/or higher humidity, the output may not always be sufficient to attain the specified value.
- The specified working voltage for the regulating valve must be greater than 0.3 A in order to ensure that the regulating valve will be actuated.
- At setting "maximum cooling performance", the actuating voltage is regulated to about 0.8 A (displayed in Read measuring Value Block).
- In terms of absolute pressure, 0 bar corresponds to absolute vacuum. The normal ambient pressure (positive pressure) corresponds to 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (identifiable through the valve -1 below 0).
If specified reading is not obtained, compare results of all three tests.
Observed refrigerant pressures / cooling performance results
Observed refrigerant pressures / cooling performance results
Observed refrigerant pressures / cooling performance results
Observed refrigerant pressures / cooling performance results
