Sprinter 2500 L5-2.7L DSL Turbo (2003)
Evaporator Temperature Sensor / Switch: Description and Operation
Evaporator Temperature Sensor
Front
The evaporator temperature sensor is a two-wire temperature sensing element located at the coldest point on the face of the evaporator. The sensor is
attached to the evaporator coil fins. The evaporator temperature sensor prevents condensation on the evaporator coil from freezing and obstructing A/C
system air flow. The evaporator temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
The evaporator temperature sensor monitors the temperature of the evaporator. The sensor will change its internal resistance in response to the
temperatures it monitors. The ATC control module is connected to the sensor through a sensor ground circuit and a sensor signal circuit. As the
evaporator temperature increases, the resistance of the sensor decreases and the voltage monitored by the module decreases. The module uses this
monitored voltage reading to an indication of the evaporator temperature. The ATC control module is programmed to respond to this input by cycling
the air conditioning compressor clutch as necessary to optimize air conditioning system performance and to protect the system from evaporator freezing.
The external location of the sensor allows the sensor to be removed or installed without disturbing the refrigerant in the system. The evaporator
temperature sensor is diagnosed by performing the ATC Function Test using a DRBIII(R) scan tool. Refer to Computers and Control Systems/ Body
Control Module / Testing and Inspection / Procedures.
Rear
The rear evaporator temperature sensor is used to signal the rear A/C control module to cycle the rear A/C solenoid valve open and closed in order to
control rear evaporator temperature. Controlling the evaporator temperature prevents condensation on the evaporator fins from freezing and obstructing
rear air conditioning system air flow.
The rear evaporator temperature sensor 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 rear 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 signal to the rear A/C control module.
When the rear evaporator temperature sensor sees a temperature input below about 1.6° C (35° F), it signals the rear A/C control module to cycle the
rear A/C solenoid valve closed. When the temperature input reaches above about 3.9° C (39° F), the switch signals the control module to cycle the valve
open.
The rear evaporator temperature sensor can be accessed for service by removing the air inlet grate from the rear evaporator housing. The rear evaporator
temperature sensor cannot be adjusted or repaired. If faulty or damaged, the sensor must be replaced.
