Bulletin 30-020.007
Copyright © 2019 Unico Inc. Page 25
To measure the superheat, use the following:
1. Measure and record the suction pressure at the
evaporator outlet using an accurate refrigerant
gauge. If this is not possible, measure the pressure
at the service port on the suction valve fitting at the
condensing unit and add the estimated pressure loss
in the suction line between the condensing unit and
evaporator. Record the corresponding saturation
temperature for this pressure (see Table 10).
2. Measure the suction line temperature at the
evaporator outlet using an accurate metal or glass
thermometer, or thermocouple. Insert the
thermometer under the insulation on the suction
line and tape firmly against the surface of the
suction tube.
3. Determine the superheat with the following
equation:
Suction Line Temperature
— Saturated Temperature
= Superheat
Charging by Gauge Pressures It is not possible to
charge the system by gauge pressures. Gauge pressure
should only be used to verify the system is working
properly.
The Unico System will show a lower suction pressure
during the cooling mode than a conventional system.
Generally, it will be 10 to 15 psi (70 to 100 kPa) less.
For example, a normal suction pressure for the Unico
System will be about 114 psig (786 kPa) with an 85 to
95°F (29 to 35°C) outdoor temperature. Expect lower
pressures when the outdoor temperatures are lower.
The head pressures should be similar to a conventional
system when in the cooling mode.
Table 11. R410A Saturation Pressure -
Temperature
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