F.Diagnosis and Service Procedures

1. WHITE AREA DIAGNOSIS AND SERVICE

White area diagnosis means that all components of the refrigerant system are functioning properly. If insufficient cooling exists, air handling system is at fault. Check for:

a. Temperature door setting. Make sure temperature control is set to full cold position. Check and adjust for proper closing.

2. GRAY AREA DIAGNOSIS AND SERVICE

Check the following if pressures intersect in the gray area:

a. Improper condenser operation. This can result from:

- Extremely high ambient humidity.
- Insufficient air flow across the condenser.
- Damaged or dirty condenser fins.
- Defective cooling fan.
- Improperly calibrated high pressure fan switch.
- Faulty fan relay.

b. High side refrigerant restriction. Feel liquid line before expansion tube (orifice). If line feels cold, it indicates restriction in high side. Visually check for frost spot to locate restriction and repair as necessary.

c. Refrigerant system overcharged (high discharge and high suction pressures). See below.

d. Orifice tube blocked (low suction pressures). See below.

e. Air in system (high discharge and high suction pressures). See below.

Items c, d, and e above can be corrected by the same procedure:

- Discharge refrigerant system slowly using the low pressure fitting to prevent oil loss.
- Check orifice tube for blockage. Clean or replace as required (small amount of metal chips may be normal).
- Evacuate system to a vacuum (improper evacuation of system prior to recharge will cause air to remain in system).
- Recharge system with proper amount of refrigerant.
- Leak check system.
3. BLACK AREA DIAGNOSIS AND SERVICE

Check the following if pressures intersect in the black areas:

a. Compressor may be internally damaged. If suction and discharge pressures are equal and do not change when the A/C mode is turned on and off, the compressor may be internally damaged. Excess heat at the clutch surfaces or a free wheeling clutch driver are signs of internal compressor damage. When replacing the compressor, follow component replacement procedures to maintain the correct oil charge in the system. Failure to do so may cause excessive noise and early compressor failure.

b. Missing expansion tube (orifice). Feel liquid line after expansion tube. If line is warm, discharge system and inspect for presence of expansion tube. If expansion tube or O-ring is missing, install new one in system. If expansion tube is present, remove, clean, or replace tube as necessary and install in system. Evacuate and charge system.

c. Compressor at minimum stroke. If compressor discharge pressure remains only 10-30 psi above suction pressure, compressor may be at minimum stroke. When noted, run engine at approximately 3000 rpm for three minutes until pressures become normal. During this period, cycle mode lever from vent to A/C every 20 seconds. If no change, perform control valve low load test.

d. Compressor control valve set improperly. Run low load test to verify. Follow this procedure exactly. It is designed to create a low cooling load causing the V5 compressor to go toward minimum stroke which is absolutely necessary for evaluation of control valve set point.

FIGURE 1 - TESTING HOOKUP:

- Connect gage set (Figure 1) to high and low A/C Service fittings.
- Check gage accuracy by reading both gages. Correct gages as necessary.
- Disconnect blower motor.
- Set test conditions:
1. Start engine and run at fast idle speed.
2. Open hood, close windows and doors.
3. Set A/C controls to LOW blower and MAX cooling.
- Record and evaluate test results:
1. If suction pressure is 25-35 psi, control valve is functioning properly.
2. If suction pressure is outside limits of 25-35 psi, replace control valve.
e. Refrigerant system undercharged. This condition may exist when suction pressure is below 35 psi during the high load test. The accumulator (A/D) and the suction line before the A/D, will be warm if charge is low. Add one can of refrigerant and recheck. Pressures should come into white area. If so, find source of refrigerant loss and repair leak. Evacuate and charge system with correct refrigerant amount.

f. Expansion Tube (orifice) Blocked. See Step e in Grey Area Diagnosis and Service.