Thermo King 920000, Manual

Page: 109 / 190

Refrigeration Maintenance
109
High Pressure Cutout Switch
(HPCO)
The HPCO is located on the compressor. If the
discharge pressure rises above the switch setting
470 psi (3241 kPa) the HPCO opens and
de-energizes the 8H circuit, which stops the unit.
To test the HPCO, rework a gauge manifold as
shown in the High Pressure Cutout Manifold
illustration and use the following procedure.
1. Connect the gauge manifold to the compressor
discharge service valve with a heavy duty,
black jacketed thick wall #HCA 144 hose with
a 900 psi (6204 kPa) working pressure rating.
2. Set both thermostats well below the
compartment temperatures so both
evaporators run in Cool and the condensing
unit runs in high speed.
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).
4. 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.
1. Relief Valve (66-6543)
2. O-Ring (33-1015)
3. Adapter Tee Weather Head (No. 552x3)
Figure 59: High Pressure Cutout Manifold