Temperature Sensors - Lennox MS8 SERIES Installation And Service Procedures

TEMPERATURE SENSORS (LOCATION, FUNCTION AND TROUBLESHOOTING)
Refer to tables 15, 16 and 17 for sensor resistance valves and figure 63 for location of sensors.
INDOOR UNIT
1. Indoor Air Temperature Sensor (RT1): This sensor measures the return air temperature coming into the indoor coil
and sends this information to the indoor and outdoor controls.
2. Indoor Coil Temperature Sensor (RT2): This sensor is located on one of the copper tubes of the indoor coil. This sensor
is used to:
S
Control the electronic expansion valve (EEV) in cooling mode;
S
Prevent freezing. During cooling operation, if the temperature drops abnormally, the compressor speed is
decreased. If the temperature continues to fall, the compressor will be cycled OFF;
S
Terminate defrost cycle.
OUTDOOR UNIT
1. Outdoor Coil Temperature Sensor (RT3): This sensor is located on one of the copper tubes of the outdoor coil. This
sensor is used to:
S
Control the electronic expansion valve (EEV) in heating mode;
S
Protect the system from high temperatures during cooling mode;
S
Terminate defrost cycle.
2. Outdoor Air Temperature Sensor (RT4): This sensor measures the outdoor air temperature coming into the outdoor
coil and sends this information to the outdoor controls.
3. Discharge Line Temperature Sensor (RT5): This sensor is used to monitor the discharge line temperature. If the
temperature of the discharge pipe rises abnormally, the compressor speed is decreased. If the temperature continues
to rise, the compressor will be cycled OFF.
Page 47
Corp. 1244-L9