Thermo King SB-190 30, Manual

Page: 70 / 119

Refrigeration Maintenance (Rev. 12/03)
60
To add compressor oil pump down the compressor and
equalize the pressure to slightly positive. Disconnect the
compressor oil filter return line from the top of the compres-
sor and add the oil. Reattach the oil filter return line to the
compressor. Evacuate the compressor before opening the
service valves.
HIGH PRESSURE CUTOUT SWITCH
(HPCO)
The HPCO is located on the compressor discharge
manifold. If the discharge pressure rises above 470 psi
(3241 kPa), the HPCO opens the 8D circuit, de-energizing
the fuel solenoid. To test the HPCO, rework a gauge
manifold following the High Pressure Cutout Manifold
illustration.
1. Connect the gauge manifold to the compressor dis-
charge service valve with a heavy duty, black jacketed
thick wall #HCA 144 hose with a 900 psi (6204 kPa)
working pressure rating.
2. Use the Service Test Mode to run the unit in high speed
cool.
3. Raise the discharge pressure of the compressor first by
blocking the condenser coil air flow by covering the
condenser grille with a piece of cardboard. If this does
not raise the discharge pressure to the cutout level of
the HPCO, increase the engine speed by overriding the
throttle solenoid. This should increase the discharge
pressure enough to cause the HPCO to cut out.
NOTE: The discharge pressure should never be allowed to
exceed a pressure of 470 psi (3241 kPa).
Failure of the HPCO system to stop compressor operation
should be investigated first by checking the control circuit
operation and secondly by HPCO switch replacement.
THREE-WAY VALVE CONDENSER
PRESSURE BYPASS CHECK VALVE
A three-way valve condenser pressure bypass check valve is
used in this unit. This check valve controls the bypass flow
of refrigerant gas between the condenser inlet line and the
compressor discharge line.
The check valve is closed when the unit is running on cool,
or whenever the discharge pressure is higher than the con-
denser pressure.
1. Relief Valve (66-6543)
2. O-Ring (33-1015)
3. Adapter Tee Weather Head No. 552X3
High Pressure Cutout Manifold