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4-6
4.10 FILTER-DRIER REMOVAL
If the sight glass on the receiver appears to be flashing
or excessive bubbles are constantly moving through the
sight glass, the unit may have a low refrigerant charge, or
the filter-drier could be partially plugged.
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.
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2
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4
1. Filter-Drier Inlet Valve
2. Valve Service Port
3. Flare Nut
4. Filter-Drier
5. Filter-Drier Outlet Valve
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3
5
Figure 4-5. Filter Drier Removal
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 run control switch
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. After
remaining refrigerant has escaped, 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 flares.
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
right to left as viewed). Finger tighten flare nuts.
h. Tighten filter-drier inlet line flare nut using two
open end wrenches.
i. Open the filter-drier inlet valve slowly to purge the
filter-drier momentarily. Tighten the outlet flare nut
using two open end wrenches.
j. Immediately backseat (fully close both service
valve ports and replace valve caps.
k. Test filter-drier for leaks.
l. Check refrigerant level.
4.11 CHECKING PRESSURE SWITCHES
The recommended procedure for testing the High
Pressure Switch (HPS), Low Pressure Switch (LPS),
Condenser Fan Speed Switch (CFS), and Unloader
Pressure Switch #2 (UPS2) is to remove the the switch
from the unit and bench test as described in the following
procedure.
All pressure switches are threaded into positive shut
off connections (schrader) 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) is located on the discharge line near the roadside
evaporator fan blower assembly. (See Figure 1-1.) The
Unloader Pressure switch #2 (tan wire leads) is located
on the suction line near the roadside evaporator fan
blower assembly. (See Figure 1-1.)
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). A continuity reading
should indicate a closed switch. If the switch is good,
continue.
c. Connect switch to a cylinder of dry nitrogen as
shown in Figure 4-6.
1. Cylinder Valve and
Gauge
2. Pressure Regulator
3. Nitrogen Cylinder
4. Pressure Gauge
(0 to 500 psig =
0 to 36 kg/cm
@
)
5. Bleed-Off Valve
6. 1/4 inch Connection
7. High or Low Pressure
Switch
8. Ohmmeter
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Figure 4-6. Checking High Pressure Switch