Thermo King UT-1200, Manual

Page: 137 / 169

Refrigeration Service Procedures
137
High Pressure Cutout Switch
(HPCO) Test
The HPCO is located on the discharge line. If the
discharge pressure rises above 470 ± 7 psig (3241
± 48 kPa), the switch opens the HPCO circuit the
to run relay and stops the unit. To test the switch,
rework a gauge manifold per the following
illustration.
1. Connect the gauge manifold to the discharge
service port with a heavy duty, black jacketed
thick wall #HCA 144 hose with a 900 psig
(6204 kPa) working pressure rating.
2. Set the thermostat well below the box
temperature so that the unit will be in High
Speed Cool.
3. Raise the discharge pressure of the
compressor by blocking the condenser coil air
flow by covering the condenser with a piece of
cardboard.
NOTE: The discharge pressure should never
be allowed to exceed a pressure of 477 psig
(3289 kPa) on R-404A systems.
4. If the HPCO opens too soon or does not open
to de-energize the run relay and stop the unit,
it must be replaced.
High Pressure Cutout Switch
(HPCO) Replacement
Removal
1. Recover the refrigerant charge.
2. Disconnect the wires and remove the HPCO
from the discharge tube.
Installation
1. Apply a refrigerant Loctite to the threads of
the HPCO.
2. Install and tighten the HPCO and reconnect
the wires.
3. Pressurize the system and test for leaks.
4. If no leaks are found, evacuate the system.
5. Recharge the unit with refrigerant and check
the compressor oil.
High Pressure Relief Valve
Replacement
NOTE: Determine the cause of extremely high
discharge pressure before replacing the High
Pressure Relief Valve.
Removal
1. Recover the refrigerant charge.
2. Unscrew and remove the high pressure relief
valve from the receiver tank.
Installation
1. Apply a refrigerant oil to the O-ring of the
high pressure relief valve.
2. Install and tighten the high pressure relief
valve.
3. Pressurize the system and test for leaks.
1. Relief Valve
2. O-ring
3. Adapter Tee Weather Head
Figure 207: High Pressure Cutout Manifold