Maintenance; Driver's Unit - PREVOST H3-41 Maintenance Manual

Example of readings taken:
A/C pressure gauge at
compressor suction
converted to temperature
with chart
Temperature on remote bulb
Average of low and high
swing
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 (2,2°C) higher at the remote
bulb and have an average of 12 to 16°F (4 to
6°C) 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, increase refrigerant
flow by turning
counterclockwise on expansion valve. To
increase superheat, flow of refrigerant is
reduced by turning adjustment screw of
clockwise.
7. 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 F (0 C) on chart. If temperature
o o
reading is 40 F (4,4 C), subtract 32
o o
the result will be 8 F (4,4
o
40°F
Low swing 44°F
High swing 54°F
49°F
adjusting screw
F (0 C) and
o o
C) of superheat.
o
PA1621 Maintenance Manual All Series | Revised February 2019
SECTION 22: HEATING AND AIR CONDITIONING
CAUTION
Before proceeding with 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.
4.11.3

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
Failure to comply may result in system
damage and/or personal injury.
4.11.4

Driver's Unit

The function and operation of the driver's unit
expansion valve are similar to the central
system, but no superheat adjustment is required
( ).
FIGURE 53
the atmospheric pressure.
41