Lennox LGH094U Unit Information page 36

9-Freezestats S49 and S50
Standard and high efficiency units are equipped with a low
temperature switch (freezestat) located on the return
bend of each evaporator coil. S49 (first circuit) and S50
(second circuit) are located on the corresponding evapo­
rator coils. Ultra high efficiency units are equipped with
S49 only which is located on the return bend of the com­
mon evaporator coil.
Each freezestat is wired to the A55 Unit Controller. Each
freezestat is a SPST N.C. auto-reset switch which opens at
29°F + 3°F (‐1.7°C + 1.7°C) on a temperature drop and
closes at 58°F + 4°F (14.4°C + 2.2°C) on a temperature
rise. To prevent coil icing, freezestats open during com­
pressor operation to temporarily disable the respective
compressor until the coil warms sufficiently to melt any ac­
cumulated frost.
If the freezestats are tripping frequently due to coil icing,
check the unit charge, airflow and filters before allowing unit
back in operation. Make sure to eliminate conditions which
might promote evaporator ice buildup.
10-Temperature Sensors RT37 and RT38
Ultra high efficiency units are equipped with a temperature
sensor (thermistor) located on the back of each compres­
sor underneath the crankcase heater. The A55 Unit Con­
troller uses input from RT37 (compressor 1), RT38 (com­
pressor 2) and A185 pressure transducer to calculate sump
superheat for each compressor. The Unit Controller uses
this information to optimize system reliability.
Verify the sensor value using the menu path:
MAIN MENU > DATA > IN/OUTPUTS > SENSORS > LOCAL
Sensors should read within +/- 5 degrees of actual com­
pressor sump temperature. Make sure the sensor is mak­
ing sufficient contact with the compressor shell.
11-Pressure Transducer A185
Ultra high efficiency units are equipped with a pressure
transducer located on the common suction line. The Unit
Controller uses the input from the transducer, RT37 and
RT38 to calculate sump superheat for each compressor.
The Unit Controller uses this information to optimize sys­
tem reliability.
Verify the sensor value using the menu path:
MAIN MENU > DATA > IN/OUTPUTS > SENSORS > LOCAL
A185 should read within +/- 10 psi of actual suction pressure.
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