Recommendations For Operation At Low Temperatures - Thermo Pride OPA Installation And Service Manual

All installations and services must be performed by qualified service personnel.
Once the liquid line pressure is known, the refrigerant temperature must be taken
on the liquid line as it enters the evaporator. Use a good resistive thermometer or
thermocouple protected with a rag or insulation. Subtract the measured
temperature from the saturation temperature of the refrigerant. The result is the
degree of refrigerant subcooling.
Refer to Example 4, in Appendix B: Calculations of this manual, for a sample
calculation of how to figure the degree of subcooling for the condenser. In
general, Thermo Pride recommends the evaporator operate with a subcooling of
between 5° and 15°F.

6. Recommendations for Operation at Low Temperatures

If the cooling system will be operated with outdoor ambient air temperatures
below 65°F, Thermo Pride strongly recommends the following modifications be
made to the system to aid in promoting the longevity and durability of the
compressor.
1. To help evaporate any liquid refrigerant that accumulates in the compressor,
a crankcase heater should be installed in the compressor.
2. A low temperature (45°F minimum) ambient control (contact) should be added
to the 24-volt leg of the control circuit to the contactor coil. This contact should
act to shutdown the cooling system in the event that outdoor temperatures
drop below 45°F.
3. To assist the system in temporarily storing unneeded refrigerant charge, a
suction line accumulator should be installed in the system.
4. Test and confirm the compressor is receiving superheated vapor under the
coldest of expected operating conditions. Adjust the superheat, if required.
These items will assist in preventing liquid floodback, flooded starts, and
refrigerant migration to the compressor during off cycle. These situations are
detrimental to the service life of the compressor.
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