Thermo King MD-MT, Operator'S Manual

Page: 109 / 192

Refrigeration Maintenance
109
To check compressor oil level with an ambient air
temperature below 50 F (10 C):
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 evaporator temperature is above 32 F (0 C),
it will be necessary to force Defrost. To force
Defrost, use a jumper wire and jump the number
12 wire at the defrost relay to ground. Then push
the Manual Defrost switch. Allow evaporator
temperature to rise to approximately 45 F (72 C).
Remove the jumper wire from the defrost relay.
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.
R-404A systems use a special Ester oil TK No.
203-413.
To add oil to the compressor, pump down
compressor, see “Compressor Pump Down and
Checkout.”
Compound Pressure Gauge
(Optional Equipment)
The suction pressure at the compressor is shown
on the compound pressure gauge. The compound
gauge monitors the low side pressure of the
refrigeration system.
The compound pressure gauge should be
recalibrated occasionally by comparing it with a
gauge of known accuracy or by adjusting to zero
at atmospheric pressure.
To recalibrate the compound gauge, pump down
the unit and pressurize the low side to slightly
positive (2 to 5 psig [14 to 34 kPa]). Disconnect
the gauge line and turn the adjustment screw on
the unit gauge to bring the reading to zero.
NOTE: If the compound pressure gauge does
not stay in calibration, replace the compound
gauge.
High Pressure Cutout (HPCO)
The high pressure cutout is located on the
compressor cylinder head. If the discharge
pressure rises above 450 psig (3103 kPa) on
R-404A and R-502 units, the switch opens the 8
circuit, de-energizing the fuel solenoid. To test the
switch, rework a gauge manifold per illustration.
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 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.
1. Relief Valve (66-6543)
2. O-ring (33-1015)
3. Adapter Tee Edelmann (P/N 22-7200)
Figure 59: High Pressure Cutout Manifold