1B-6 AIR CONDITIONING Expansion Valve This expansion valve is external pressure type and it is installed at the evaporator intake port. The expansion valve converts the high pressure liquid refrigerant sent from the receiver/drier to a low pressure liquid refrigerant by forcing it through a tiny port before sending it to the evaporator. This type of expansion valve consists of a temperature sensor, diaphragm, ball valve, ball seat, spring adjust- ment screw, etc. The temperature sensor contacts the evaporator outlet pipe, and converts changes in temperature to pressure. It then transmits these to the top chamber of the dia- phragm.
The refrigerant pressure is transmitted to the dia- phragms bottom chamber through the external equaliz- ing pressure tube. The ball valve is connected to the diaphragm. The open- ing angle of the expansion valve is determined by the force acting on the diaphragm and the spring pressure. The expansion valve regulates the flow rate of the refrig- erant. Accordingly, when a malfunction occurs to this ex- pansion valve, both discharge and suction pressures get low, resulting in insufficient cooling capacity of the evaporator. For R-134a air conditioning, the expansion valve cali- bration has been changed from R-12 to match the R- 134a characteristics.
1 2 N1A0212E Evaporator The evaporator (1) cools and dehumidifies the air before the air enters the vehicle. High-pressure liquid refriger- ant flows through the expansion valve into the low-pres- sure area of the evaporator.The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the air. As heat is lost between the air and the evaporator core surface, moisture in the vehicle condenses on the out- side surface of the evaporator core and is drained off as water. When the evaporator malfunctions, the trouble will show up as inadequate supply of cool air.
The causes is typi- cally a partially plugged core due to dirt, or a malfunc- tioning blower motor. The evaporator core with a laminate louver fin is a sin- gle-sided tank type where only one tank is provided un- der the core. N1A0051E Legend 1. Expansion valve 2. Insulator 3. Evaporator core N1A0050E