| It has taken me some time to understand Nissan's air conditioning design philosphy. The a/c in the Z and other Nissan vehicles is unlike any system I have ever worked with. My previous experience had always been with "clutch cycling" systems of both EXPANSION VALVE or ORIFICE TUBE design type. The a/c in our beloved Z is operates with a constantly energized compressor clutch and an expansion/bypass, oil filled tube operated valve. Some Background: 1. Exp Valve systems - oil in a tube with a bulb at the end, in thermal contact with the evaporator and connected to the expansion valve, expands and contract in response to temperature. The system is calibrated to shut off the refrigerant expanding into the evaporator as well as the compressor clutch when the evaporator temperature reaches near 34F. These valves have a spring load that could be altered with a "temperature" button. 2. Orifice Tube systems - a pressure switch on the accumulator bottle shuts off the compressor clutch power in response to a pressure/temperature relationship that deteremines the temperature at the evaporator. The expansion at the orifice tube is "uncontrolled" and cabin temperature is adjusted by blending in heated air that has passed through the heater core.
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