Thermo King 002008, Manual

Page: 87 / 155

87
Refrigeration Service Operations
NOTE: It is generally good practice to replace
the filter drier whenever the high side is opened
or when the low side is opened for an extended
period of time.
Low Side Pump Down
NOTE: Operate all the evaporators in Cool for
2 to 5 minutes with the service valves in their
normal operating positions before performing
the low side pump down. Install a gauge
manifold at the compressor.
1. Run all the evaporators in cool, front seat the
receiver tank outlet valve and the bypass hand
valve, and pump down the low side to 20 to
25 in. Hg vacuum (-68 to -85 kPa). Turn the
Zone 1/Host On/Off switch Off.
If the unit pumps down acceptably and then
holds at least 15 in. Hg vacuum (-51 kPa) for
2 minutes or more, it can be assumed that the
receiver tank outlet valve, the compressor
discharge valve plates, the HGS solenoid, the
HGS2 solenoid, the HGS3 solenoid, and the
purge valve solenoid are sealing acceptably.
2. Prepare to perform service on the unit’s low
side by equalizing the high side and low side
pressures.
a. Disconnect the purge valve solenoid wires
from the main wire harness.
NOTE: If the purge valve solenoid wires are
not disconnected from the main wire
harness, the purge valve is energized when
the unit is placed in the Evacuation mode.
This allows the refrigerant in the condenser
to flow into the accumulator, undoing the
low side pump down.
b. Place the unit in the Evacuation mode.
Refer to the Service Test mode in the
appropriate Microprocessor Diagnosis
Manual. The high and low side pressures
should equalize in the Evacuation mode.
NOTE: Repeat the pump down procedure
if the pressures equalize above 20 psi
(138 kPa). If suitably low pressures cannot
be achieved after the third pump down, the
refrigerant must be recovered to perform
service on the low side.
c. If the reading on the gauge manifold’s
high pressure gauge increases after the
high and low side pressures have been
equalized, the condenser inlet check valve
is leaking.
d. Remember to reconnect the purge valve
solenoid wires to the main wire harness
when the service procedures have been
completed.
Compressor
The 7-quart sump extends below the top of the
lower frame rails. Therefore, a flat board cannot
be used as a support when removing or installing
a compressor with a 7-quart sump. A Compressor
Installation Tool P/N 204-1087 (two pieces) has
been developed to aid in the removal and
installation of the 7-quart sump compressors.
Removal
1. Pump down the low side and equalize the
pressure to slightly positive.
2. Loosen the compressor belts on Model 50
units.
3. Front seat the discharge and suction service
valves. Remove the remaining refrigerant
pressure from the compressor.
4. Unbolt the discharge and suction service
valves from the compressor.
5. Remove the compressor oil filter and its lines.
6. Disconnect the HPCO wires and the HPSW
wires.