RAM 1500 Van V8-5.9L VIN Z LDC (2001)
Evaporator Temperature Sensor / Switch: Description and Operation
A/C FIN SENSING CYCLING CLUTCH SWITCH
The fin sensing cycling clutch switch is used on this model to signal the Powertrain Control Module (PCM) to cycle the compressor clutch ON
and OFF in order to control the evaporator temperature. Controlling the evaporator temperature prevents condensate water on the evaporator fins
from freezing and obstructing air conditioning system air flow.
Fig. 7 Fin Sensing Cycling Clutch Switch
The fin sensing cycling clutch switch consists of a probe and a switch unit. The probe, which is a Negative Temperature Coefficient (NTC)
thermistor in a capillary tube, is inserted between the front evaporator coil fins to monitor evaporator temperature. The switch unit contains
internal control logic that monitors the input from the probe in order to switch an internal transistor that controls the output to the PCM.
When the fin sensing cycling clutch switch sees a temperature input below about 1.6 °C (35 °F), it signals the PCM to cycle the compressor OFF.
When the temperature input reaches above about 3.9 °C (39 °F), the switch signals the PCM to cycle the compressor back ON.
The fin sensing cycling clutch switch can be accessed for service by removing the screws and carefully lifting the front of the top cover up from
the heater-A/C housing. The fin sensing cycling clutch switch is a sealed unit and cannot be adjusted or repaired. If faulty or damaged, the switch
must be replaced.