SECTION 22: HEATING AND AIR CONDITIONING
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
37
compressor suction
converted to temperature
with chart
Temperature on remote bulb
Low swing 44°F
High swing 54°F
Average of low and high
swing
49°F
Formula for superheat
T° at bulb – T° suction = T° superheat
49°F
‒
40°F = 9°F
NOTE
The low swing of the superheat should be a
minimum of 4°F higher at the remote bulb and
have an average of 8 to 12°F higher range at
the bulb than the fitting at the expansion valve.
NOTE
The thermal expansion valve has a MOP
(maximum operating pressure) of 55 psi. At
this setting, the valve is completely opened.
If the temperature at the bulb is greater than
50°F, do not try to adjust superheat as the
valve is almost completely opened.
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 converted
to 32
o
F on chart. If temperature reading is 40
o
F,
subtract 32
o
F and the result will be
8
o
F 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.
2. Disconnect the external equalizer line from
the underside of the power head, and
unclamp the remote control bulb from the
evaporator coil outlet line.
3. Remove the two cap screws holding the
power assembly to the valve body flange.
Lift off the power assembly and remove the
cage assembly.
4. When reassembling, replace with the new
gaskets in proper location. Make sure the
two lugs on the cage assembly fit into
grooves provided in the power assembly.
Do not force the valves together. The cage
must fit properly before tightening the body
flange. Tighten bolts evenly.
5. Check for leaks.
Safety Instructions
1. Make sure the valve is installed with the
flow arrow on the valve body corresponding
to the flow direction through the piping
system.
2. Before opening any system, make sure the
pressure in the system is brought to and
remains at the atmospheric pressure.
Failure to comply may result in system
damage and/or personal injury.
7.10.2 Driver’s HVAC Unit
The function and operation of the expansion
valve for the driver’s HVAC unit are similar to the
passengers’ HVAC unit but no superheat
adjustment is required (see
FIGURE 3
and
FIGURE
41
).
7.11 TORCH BRAZING
Use electrode containing 35% silver.
CAUTION
When using heat near a valve, wrap with
water saturated rag to prevent overheating of
vital parts.
DANGER
Before welding any part of refrigeration
system, make sure the area is well ventilated.
