| Message |
3. Expansion/Bypass - in this system, the temperature of the evaporator is controlled by bypassing or preventing the refrigerant from entering the evaporator and redirecting it back towards the compressor. (My guess is that the bypass is done to expanded refrigerant as compressors do not take well to receiving liquids. Liquids are incompressible.) In 1994 Nissan changed the refrigerant to r134a. Evaporator temperature control up to 1993 (r12 cars) was purely meachanical by means of the EXP/BYPASS and THROTTLE SUCTION valves. Cars with R134a saw the replacement of the TSV by the TCA, an electronic device that "helps" to control the temperature of the evaporator, at times when the exp/bypass valve fails (I guess the TSV may have payed a similar role). This is likely when ambient temps are on the low side and an electronically climate controlled car runs the a/c in order to adjust the temperature in the cabin. This pesky "sensor" is located on the surface of the evaporator box with its sensing element on the discharge face of the evaporator. The TCA sends a signal to the ECU if it senses a temperature below 34F. This shuts off the compressor until the sensor warms up and turns off its voltage output. In a sense one could say that TCA equipped cars are quasi clutch cyling, although the majority of the work is done by the expansion/bypass valve and clutch cycling is rather rare, particularly in the summer.
|
 |
