Thermo King 914970, Manual

Page: 121 / 186

Refrigeration Maintenance
121
After the unit has maintained the above conditions
for 15 minutes, observe the oil level. The oil
should be 1/4 to 1/2 up in the sight glass.
To check compressor oil level with an ambient air
temperature below 10 C (50 F):
Run the unit
through a complete Defrost cycle. After
completing the Defrost cycle, run the unit on Cool
for ten minutes. Observe the oil level. The oil
should be 1/4 to 1/2 up in the sight glass.
If the box is empty, you can run the unit on the
Heat cycle instead of the Defrost cycle.
NOTE: Use refrigeration compressor oil ONLY.
Polyol Ester type, P/N 203-413 is required on
R-404A.
High Pressure Cutout (HPCO)
The high pressure cutout is located on the
compressor. If the discharge pressure rises above
470 psig (3241 kPa), the switch opens the 8H
circuit to stop the unit. To test the switch, rework a
gauge manifold per the following procedure.
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 roadside condenser grille
with a piece of cardboard.
NOTE: The discharge pressure should never
be allowed to exceed a pressure of 470 psig
(3241 kPa) on R-404A systems.
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.
Compressor Pump Down and
Checkout
1. Install a gauge manifold set on the
compressor. Open the service valves (crack
the valves off of the back seated position) to
access system pressure.
NOTE: Purge air from the gauge set.
2. Set the thermostat well below box
temperature, and run the unit in Cool mode
until temperature is stabilized (at least 5
minutes).
3. Close (front seat) the suction service valve.
Pump the compressor down into a deep
vacuum (25 in.). Stop the unit. If the suction
pressure does not rise above 10 psig (69 kPa)
in 2 minutes, perform check procedures on the
three-way valve and the bypass check valve. if
the pressure does not rise, go to step 4.
1. Relief Valve
2. O-ring
3. Adapter Tee Weather Head
Figure 47: High Pressure Cutout Manifold