Section 22: HEATING AND AIR CONDITIONING
PA1562
28
FIGURE 33: SUPERHEAT ADJUSTMENT INSTALLATION22046
3. Install a remote reading thermometer to the
evaporator outlet line near the existing
remote bulb (Fig. 33).
4. Apply thermostatic tape around the bulb
and evaporator outlet line to get a true
reading of the line temperature.
5. Block condenser if necessary to keep
pressure over 150 psi.
FIGURE 34: HIGH & LOW SWING TEMPERATURE AT
REMOTE BULB
22047
6. Check approximately 5 readings of
pressure at 2-minute intervals and convert
to temperature using the temperatures &
pressures table (page 33). Likewise check
the temperature reading at the remote bulb
at the same 2-minute intervals and record
the low and high swing readings of the
needle (refer to Fig. 34).
Example of readings taken at fig. 34:
A/C pressure gauge
converted to
temperature at
expansion valve fitting
Temperature on
remote bulb
40°F (4,4°C)
Low-
swing
44°F
(6,6°C)
High
swing
54°F
(12,2°C)
Formula for superheat
49°F-40°F=9°F
(9,4°C-4,4°C = 5°C)
Average of low and
high swing is 49°F
(9,4°C)
NOTE
The low swing of the superheat should be a
minimum of 4°F (2,2°C) higher at the remote
bulb and have an average of 8 to 12°F (4 to
6°C) higher range at the bulb than the fitting at
the expansion valve.
NOTE
To reduce the superheat, flow of refrigerant is
increased by turning adjusting screw of
expansion valve lower evaporator temperature
counterclockwise. To increase temperature or
increase superheat, flow of refrigerant is
reduced by turning adjustment screw of
expansion valve clockwise.
6. Regulate suction pressure to temperature
reading according to temperature chart or to
the R-134a temperature scale on the
pressure gauge.
Example: Suction pressure 30 psi (207 kPa)
converted to 32
o
F (0
o
C) on chart. If temperature
reading is 40
o
F (4,4
o
C), subtract 32
o
F (0
o
C) and
the result will be 8
o
F (4,4
o
C) of superheat.
CAUTION
Before proceeding to the expansion valve
adjustment, check for restriction on suction
side for plugged filter dryer and partially open
valves. These conditions will give a high
superheat.
Maintenance
1. Pump down the system as previously
indicated in this section.
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