A/C Refrigerant System Pressures, Checking

A/C refrigerant system pressures, checking

Check A/C refrigerant system pressures using these three tests:

1- Air temperature drop from center instrument panel outlet (A/C system cooling performance)
2- A/C system high pressure
3- A/C system low pressure

The combined results of all three steps determine which part of the A/C system is causing the problem, refer the table given below.

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
Outside (ambient) air temperature between 20-30°C (68-86°F)
Drive belts for A/C compressor and Generator in good condition and properly tensioned

Test 1: Air temperature drop from center instrument panel outlet, checking (A/C system cooling performance)

- Start engine.
- Set temperature control to maximum "cold".
- Press "A/C" button and select second blower speed.
- Adjust air distribution to instrument panel outlets.
- Insert thermometer into center instrument panel outlet and raise engine speed to approximately 1500 RPM.

Specified result

With humidity normal and outside (ambient) temperature between 20-25°C (68-77°F), system is cooling satisfactorily if air temperature from center instrument panel vent drops below 10°C (50°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, refer the table given below.

Test 2: A/C system high pressure, checking

- Connect high and low pressure hoses of refrigerant recovery/recycling/recharging unit Kent-Moore ACR4 or equivalent, to high and low pressure service valves.
- Disconnect electrical connector from coolant fan.
- Start engine.
- Set temperature control to maximum "hot".
- Press "A/C" button and select highest blower speed.
- Adjust air distribution to footwell outlets.
- Raise engine speed to approximately 1500 RPM.

Specified result

System high pressure is normal if high-pressure gauge reads 232 psi (16 bar) within 30 seconds.

If specified reading is not obtained, also perform test 3 and compare results of all three tests, refer the table given below.

Test 3: A/C system low pressure, checking

- Connect high and low pressure hoses of refrigerant recovery/recycling/recharging unit Kent-Moore ACR4, or equivalent, to high and low pressure service valves.
- Start engine.
- Set temperature control to maximum "cold".
- Press "A/C" button and select first blower speed.
- Adjust air distribution to instrument panel outlets.
- Raise engine speed to 1500 RPM.

Specified result
System low pressure is normal if low-pressure gauge reads 22-36 psi (1.5-2.5 bar) within 30 seconds.

If specified reading is not obtained, compare results of all three tests, refer the table given below.