- Park the vehicle and set the engine speed at 1500 RPM.
- Set the HVAC controls to "MAX A/C", the blower at High-speed, and the temperature control dial to the coldest setting.
- Visually verify that the A/C compressor clutch is engaged, and the compressor is operating. Verify that the heater coolant valve is closed, and the heater coil tubes are neutral or cool to the touch.
- The suction hose fitting (at the evaporator outlet) should be cold to the touch. This fitting may sweat or even frost slightly. The liquid hose fitting (at the evaporator inlet) should be warm to the touch.
- Chilled air should be discharged from the supply louvers in the cab. After 3-5 minutes of A/C operation, the louver air temperature should be approximately 20-30 degrees (F) colder than the warmest air entering the A/C system (fresh or recirculated air).
- Air inlet/outlet temperature differentials are greatly affected by ambient temperature and relative humidity. In cool ambient conditions, differentials smaller than 30 degrees may be seen. Air can only be chilled to a certain level, and then the A/C compressor will cycle off to prevent evaporator freeze-up. High humidity may also result in smaller differentials; a large amount of cooling capacity is required to dehumidify air, as well as cool it.
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