United Technologies Carrier TRANSICOLD 68RM35-604-20, Operation And Service

Page: 31 / 45

4-7
T-288
b. Unit operation in cool mode and the
compressor
fully loaded (6-cylinder
operation) for 15 minutes.
c. Head pressure at least 150 psig (for R-134a
systems). (It may be necessary to block
condenser air flow to raise head pressure.)
Under the above conditions, the system is properly
charged when the bottom receiver sight glass
appears half full with refrigerant. If the bottom sight
glass is not half full, add or delete refrigerant
charge to the proper level.
4.10 FILTER-DRIER REMOVAL
If a pressure drop across the filter-drier is indicated
or the moisture-indicator may show an abnormal
(wet) condition, the filter-drier must be changed.
a. Check for a restricted filter. Backseat the inlet
and outlet valves of the filter-drier and attach
the gauge manifold set. Midseat both valve
and start unit. Observe the pressure reading. If
a pressure drop of more than 10 psig is
indicated the filter is plugged and must be
changed.
b. Pump down the system as outlined in section
4.4.
c. Turn the driver’s A/C switch and rear control
switch to the “OFF” position.
d. Place a new filter-drier near the unit for
immediate installation.
e. Using two open end wrenches, slowly crack
open the flare nuts on each side of the
filter-drier. Remove the filter-drier.
CAUTION
The filter-drier may contain liquid
refrigerant. Slowly open the flare nuts and
avoid contact with exposed skin or eyes.
f. Remove seal caps from the new filter-drier.
Apply a light coat of compressor oil to the
O’rings.
g. Assemble the new filter-drier to lines ensuring
that the arrow on the body of the filter-drier
points in the direction of the refrigerant flow
(refrigerant flows from left to right, as viewed).
Finger tighten flare nuts.
h. Tighten filter-drier flare nuts using two open
end wrenches.
i. Install vacuum pump on filter drier inlet valve.
Evacuate to 500 microns and disconnect
vacuum pump.
j. Open both inlet and outlet valves.
k. Test filter-drier for leaks.
l. Check refrigerant level.
1 2 3 4
1. Valve Service Port
2. Filter-Drier Inlet
Liquid Line Valve
3. Flare Nut
4. Filter-Drier
5. Filter-Drier Outlet
Liquid Line Valve
1 3 5
Figure 4-5. Filter-Drier Removal
4.11 CHECKING PRESSURE SWITCHES
The recommended procedure for testing the High
Pressure Switch (HPS), Low Pressure Switch
(LPS),
Condenser Fan Switch (CFS) and
Unloader Pressure Switches #1, #2 & #3 (UPS1,
UPS2 & UPS3) is to remove the switch from the
unit and bench test it as described in the following
procedure.
All pressure switches are threaded into positive
shut off valve connections (schrader valves) to
allow easy removal and installation without
pumping down or removing refrigerant from the
unit. All wire leads to the switches are quick
disconnects.
The High Pressure Switch (black wire leads) and
Low Pressure Switch (red wire leads) are located
on the compressor. The Condenser Fan Speed
Switch (gray wire leads) and the Unloader
Pressure Switch #3 (white wire leads) are located
on the discharge line above the curbside
evaporator fan blower assembly. The Unloader
Pressure Switches #1 and #2 are located on the
suction line near the curbside evaporator motor.
If the switch does not function as described below,
the switch is defective and should be replaced.
a. Remove switch from the unit.
b. Connect an ohmmeter across switch leads
(with no pressure applied to the switch) and
check for continuity. Low Pressure Switch
(LPS) and Unloader Pressure Switch (UPS3)
will show no continuity (switches will be open).
(See Table 4-1.)
c. Connect switch to a cylinder of dry nitrogen as
shown inFigure 4-6.