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, See table.

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" (if Manual A/C) or "LO" (if Climatronic).
- Manual A/C: press "A/C" button and select second blower speed.
- Climatronic: Select minimum blower speed (manual override) by pressing "decrease blower speed" button (observe front "blower speed" display in control head).
- 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 See table.

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" (if Manual A/C) or "HI" (if Climatronic).
- Manual A/C: 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 See table.

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" (if Manual A/C) or "LO" (if Climatronic).
- Manual A/C: press "A/C" button and select first blower speed.
- Climatronic: Reduce blower speed to lowest setting (manual override) by pressing "decrease blower speed" button (observe front "blower speed" display in control head).
- 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 See table.