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

1. Overfilling with refrigerant oil can occur when compressor is replaced and the total system refrigerant oil quantity is not adjusted. Refrigerant oil distribution.