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All installations and services must be performed by qualified service personnel.
5. Evaporator Superheat:
Before taking a superheat measurement allow the system to stabilize for 15
minutes under continuous operation. To measure superheat at the evaporator, a
suction pressure reading at the outlet of the evaporator would be desirable. Since
most residential cooling systems (including Thermo Pride evaporators) do not
provide a test port (sometimes referred to as a Schraeder port) at the evaporator,
the suction pressure must be read at the suction inlet to the compressor.
Typically, it would be necessary to compensate for the pressure drop through the
line connecting the evaporator and the compressor. However, due to the close
proximity of these components, the pressure drop will be small and can be
neglected. A good resistive-type thermometer or thermocouple-based sensor
should be used to measure the suction line temperature exiting the evaporator.
On evaporators using thermal expansion valves, read the temperature directly
under the expansion bulb, located on the side of the suction line exiting the
evaporator.
Measure refrigerant temperature at the 2:00 or 10:00 positions on the outer
surface of the evaporator suction tube. Wrap the thermometer or thermocouple
with a rag, or insulation, to insure system airflow does not influence the
temperature readings.
Refer to Example 3, in Appendix B: Calculations of this manual, for a sample
calculation of how to figure the degree of superheat for the evaporator. In
general, Thermo Pride recommends an operating evaporator superheat of
between 5° and 12°F.
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