W/ Fixed Displacement Compressor

A/C Performance Chart:

HUMIDITY
Humidity (the amount of moisture in the air) has an important bearing on the temperature of the air delivered to the vehicle's interior. It is important to understand the effect humidity has on the performance of the system. When humidity is high, the evaporator has to perform a double duty. It must lower the air temperature and the temperature of the moisture carried in the air. Condensing the moisture in the air transfers a great deal of heat energy into the evaporator fins and tubing. This reduces the amount of heat the evaporator can absorb from the air. High humidity greatly reduces the evaporator's ability to lower the temperature of the air delivered to the vehicle interior. Evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing some of the moisture out of the air entering the vehicle adds to the comfort of the passengers.

However, an owner may expect too much from their air-conditioning system on humid days. A performance test is the best way to determine whether or not the system is performing up to standard. This test also provides valuable clues to the possible cause of trouble.

CAUTION: Review General Information "Safety Precautions" before proceeding with this procedure.

This test requires the use of a "Manifold Gauge Set".

CAUTION: Air temperature in test room must be 70°F (21°C) minimum for this test.

1. Connect a tachometer and manifold gauge set.
2. Set control to A/C, RECIRC, PANEL, or MAX A/C, temperature lever on full cool, and blower on high.
3. Start engine and adjust to 1000 rpm with A/C clutch engaged.
4. Engine should be warmed up with doors and windows closed.
5. Insert a thermometer in the left center A/C outlet and operate the engine for 5 minutes. The A/C clutch may cycle depending on ambient conditions.
6. With the A/C clutch engaged, compare the discharge air temperature to the A/C Performance Temperature Chart.
7. Disconnect the gray vacuum line going to the heater water control valve. Observe the valve arm for movement as the line is disconnected. If it does not move, refer to the heater valve controls sections of this group. Plug the vacuum line to prevent leakage.
8. Operate the A/C for 2 more minutes and take the discharge air temperature reading again. If the temperature increased by more than 5°F (2°C), check the blend air door for correct operation. If the temperature does not increase more than 5°F (2°C), compare the discharge air temperature, suction, and discharge pressures with the values in the performance chart corresponding with the ambient temperature. Connect the gray vacuum line.
9. If the discharge air temperature fails to meet the specifications in the performance temperature chart, refer to Refrigerant System Diagnosis for further test information.