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TK 54343-18-MM-EN
Refrigeration Maintenance
Evacuating and Charging the Refrigeration System
Checking the Refrigerant Charge
If the unit has an insufficient charge of refrigerant, the evaporator will be “starved” and the box temperature will rise
even though the unit is operating. Also, an insufficient charge does not circulate enough oil to properly lubricate the
compressor. The charge can be determined by inspection of the refrigerant through the sight glass with the following
conditions established:
Testing the Refrigerant Charge with an Empty Box
1. Install gauge manifold set on the on the engine driven compressor.
2. If the unit is equipped with Electric Standby, operate the unit in Cool on Electric Standby for 5 minutes.
a. Connect the power cord.
b. Turn the unit ON and place the unit in Cool Mode for 5 minutes.
c. Turn the unit OFF and disconnect the power cord.
3. Start the vehicle’s engine and operate it at 1000 RPM.
4. Turn the unit ON and place the unit in Cool Mode. Lower the setpoint(s) to the following:
• R-134a: 25 degrees F (-4 degrees C)
• R-404A: 0 degrees F (-18 degrees C)
• R-452A: 0 degrees F (-18 degrees C)
5. Operate the unit until the following box temperature(s) are reached:
• R-134a: 35 degrees F (2 degrees C)
• R-404A: 10 degrees F (-12 degrees C)
• R-452A: 10 degrees F (-12 degrees C)
6. Check to ensure the following discharge pressures are met or exceeded:
• R-134a: 180 psig (1241 kPa)
• R-404A: 275 psi (1896 kPa)
• R-452A: 275 psi (1896 kPa)
NNoottee:: Partially blocking the condenser grille may be necessary to achieve these pressures.
7. Inspect the sight glass.
• NO BUBBLES PRESENT: The system is full of refrigerant. Proceed to Step 8.
• BUBBLES PRESENT: The system is low on refrigerant. Proceed to the “Suction (Low Side) Bump Charging”
procedure listed below.
8. Verify the unit is not over charged. Elevate engine RPM to 3000-4000 RPM for three minutes. Verify that the unit
does not shutdown on high head pressure. If unit shuts down on high head pressure the system is overcharged.
Reduce the refrigerant charge amount until the unit no longer shuts down on high head pressure.
NNoottee:: If the condenser coil was covered in previous Step 6 leave the condenser coil covered for Step 8.
Testing the Refrigerant Charge with a Loaded Box
1. Install gauge manifold set on the on the engine driven compressor.
2. Run the unit in Cool on engine driven compressor operation.
3. Cover the condenser to drive any excess refrigerant from the condenser into the receiver tank.
4. As the head pressure rises, check the liquid line sight glass. There should be no bubbles in the flow of refrigerant
through the liquid line sight glass. Bubbles in the refrigerant indicate the unit is low on refrigerant. Refer to the
“Suction (Low Side) Bump Charging” procedure listed below to top-off the system.
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