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Refrigeration Maintenance
NOTE: The following procedures involve
servicing the refrigeration system. Some of these
service procedures are regulated by Federal, and
in some cases, by State and Local laws.
In the USA all regulated refrigeration service
procedures must be performed by an EPA
certified technician, using approved equipment
and complying with all Federal, State and Local
laws.
Refrigerant Charge
Testing The Refrigerant Charge With
An Empty Trailer
If the unit has an insufficient charge of refrigerant,
the evaporator will be “starved” and the box
temperatures will rise even though the unit is
operating. The suction pressure will drop as the
refrigerant charge decreases. If the unit has an
overcharge of refrigerant, the unit may not cool
properly and the suction and discharge pressure
may be high. The charge may be determined by
inspection of the refrigerant through the receiver
tank sight glasses with the following conditions
established:
1. Place a test box over the evaporator.
2. Install a gauge manifold.
3. Use the Service Test Mode to run the unit in
high speed cool. Refer to the appropriate
Diagnostic Manual for specific information
about the Service Test Mode.
4. Use the microprocessor thermometer to
monitor the return air temperature.
5. Run the unit on high speed cool until the air in
the box is at 0 F (-18 C). By allowing the box
to leak a small amount, you will be able to
maintain 0 F (-18 C).
6. The suction pressure should be 13 to 18 psig
(90 to 124 kPa).
7. The discharge pressure should be at least 275
sag (1896 kPa). If the pressure is below this, it
can be raised by covering a portion of the
condenser grille with a piece of cardboard to
block condenser airflow.
8. Under these conditions, refrigerant should be
visible in the receiver tank sight glass. If
refrigerant is not visible in the receiver tank
sight glass, the unit is low on refrigerant.
Testing the Refrigerant Charge with
a Loaded Trailer
1. Install a gauge manifold.
2. Use the Service Test Mode to run the unit in
high speed cool. Refer to the appropriate
Diagnostic Manual for specific information
about the Service Test Mode.
3. Build up and maintain 275 psig (1896 kPa) of
head pressure. If the pressure is below this, it
can be raised by covering the roadside
condenser grille with a piece of cardboard to
block condenser air flow.
4. Cool the compartment to the lowest
temperature required.
5. Check suction pressure. It should be 13 to 25
psig (90 to 165 kPa).
6. Under these conditions, refrigerant should be
visible in the receiver tank sight glass. If
refrigerant is not visible in the receiver tank
sight glass, the unit is low on refrigerant.
Testing for an Overcharge
Use the following procedure to identify a Thermo
King unit with an excessive refrigerant charge:
1. Install a calibrated gauge manifold on the
compressor.
2. Use the Service Test Mode to run the unit in
high speed cool. Refer to the appropriate
Diagnostic Manual for specific information
about the Service Test Mode.
3. Operate the unit in high speed cool long
enough to stabilize system pressures and
reduce the box temperature to approximately
60 F (16 C) or colder.
4. Observe discharge pressure and cover the
condenser to increase the discharge pressure
approximately 75 to 100 psig (500 to 690 kPa)
above observed pressure.
