Thermo King 920000, Manual

Page: 117 / 190

117
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.
Commissioning Unit
The following procedure should be followed after
any of these conditions:
• The compressor has been replaced
• There has been a large oil loss in the system
• There has been a complete clean up or flush of
the refrigeration system.
1. Set both zone thermostats to their highest
setpoint.
If the ambient temperature is above set point
range, jump power from the 2 circuit to HGS
and RHGS to allow the valves to open.
2. Run the unit for ten minutes to allow for
wetting of the system.
3. Set both zones for Cool (remove jumpers if
installed in the previous step).
Low Side Pump Down
NOTE: Operate both 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 both evaporators in Cool, front seat the
receiver tank outlet valve, and pump down the
low side to 20 to 25 in. Hg vacuum
(-68 to -85 kPa). Press the
O
FF
key. 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
RHGS 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.
b. Remove the CYCLE-SENTRY module
from the option board to prevent the Auto
Start system from preheating and cranking
the engine.
c. Keep the Zone 1 thermostat set for Cool
and press the
O
N
key to turn the Zone 1 on.
Set the Zone 2 thermostat for Heat and
press the
O
N
key to turn the Zone 2 on.
Leave Zone 2 turned on for 1/2 second.
The gauge manifold’s high pressure gauge
will indicate a pressure decrease and the
low pressure gauge will indicate a pressure
increase when the RHGS solenoid opens.
d. Press the
O
N
key to turn Zone 2 off. Set the
Zone 1 thermostat for Heat and leave Zone
1 turned on for 1/2 second. The gauge
manifold’s high pressure gauge will
indicate a pressure decrease and the low
pressure gauge will indicate a pressure
increase when the HGS solenoid opens.
e. Set both the thermostats for Heat and press
the
O
N
key to turn both zones on. The
manifold’s high and low pressure gauges
will equalize.
NOTE: If the box temperatures are high, the
HGS and RHGS solenoids must be energized
with a test lead.
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.
f. 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.
g. Remember to replace the
CYCLE-SENTRY module and reconnect
the purge valve solenoid wires to the main
wire harness when the service procedures
have been completed.