Evaporator Temperature Sensor / Switch: Description and Operation
CIRCUIT OPERATIONElectronic Thermostat
The electronic thermostat senses the temperature of cool air from the evaporator by means of the evaporator temperature sensor. This information determines whether the thermostat will provide ground to the thermo switch relay. When the temperature becomes too low, ground is not provided.
OFF: Below 1.0 ± 0.5 °C (33.8 ± 0.9 °F)
ON: Above 3.5 ± 0.3 °C (38.3 ± 0.9 °F)
Electronic Thermostat
The thermostat consists of the duct sensor and thermostat unit which functions electrically to reduce the noises being generated while the system is in operation.
The electronic duct sensor is mounted at the evaporator core outlet and senses the surface temperature of the evaporator core. Temperature signals are input to the thermostat unit. This information is compared by the thermo unit and results in the output to operate the A/C thermostat relay and turn the magnetic clutch ON or OFF to prevent evaporator freeze-up.
A characteristic of the sensor is that the resistance decreases as the temperature increases and the resistance increases as the temperature decreases.