Dodge RAM 1500 1998 Owner's Manual page 2509

24 - 22 CONTROLS
EVAPORATOR TEMPERATURE
SENSOR
DESCRIPTION
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 dam-
aged, it must be replaced.
OPERATION
The evaporator temperature sensor monitors the
temperature of the evaporator. The sensor will
change its internal resistance in response to the tem-
peratures it monitors. The A/C-heater 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 tempera-
ture. The A/C-heater control module is programmed
to respond to this input by cycling the air condition-
ing compressor clutch as necessary to optimize air
conditioning system performance and to protect the
system from evaporator freezing. The external loca-
tion of the sensor allows the sensor to be removed or
installed without disturbing the refrigerant in the
system. The evaporator temperature sensor is diag-
nosed using a DRBIII scan tool. Refer to Body Diag-
nostic Procedures.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the HVAC housing from the vehicle
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL).
(3) Disconnect the HVAC wire harness connector
from the evaporator temperature sensor (Fig. 20).
(4) Disassemble the HVAC housing to gain access
to the evaporator coil (Refer to 24 - HEATING & AIR
CONDITIONING/DISTRIBUTION/HVAC HOUSING
- DISASSEMBLY).
(5) Remove the evaporator temperature sensor
probe from the evaporator coil (Fig. 21).
INSTALLATION
(1) Install the evaporator temperature sensor
probe into the evaporator coil.
Fig. 20 Evaporator Temperature Sensor Wire
Connector
1 - HVAC HOUSING
2 - EVAPORATOR TEMPERATURE SENSOR
3 - HVAC WIRE HARNESS
Fig. 21 Evaporator Temperature Sensor Probe
1 - EVAPORATOR COIL
2 - EVAPORATOR TEMPERATURE SENSOR PROBE
3 - BLEND DOOR
4 - HVAC HOUSING
DR