Checking The Refrigerant Charge - Thermo King V-500 Series Manual

Refrigeration Maintenance
8. When the system reaches 500 microns, close
the vacuum valve at the evacuation station
manifold. The system is now ready to charge.
9. Close the low side valve on the gauge
manifold, leave the high side valve on the
gauge manifold open, and open the valve on
the refrigerant drum to deliver liquid.
10. Allow 2.60 lb (1.20 kg) of R-134a or 2.75 lb
(1.25 kg) of R- 404A refrigerant to enter the
system. Then close the valve on the refrigerant
drum and the high side valve on the gauge
manifold.
11. Start the unit on engine operation and run the
truck engine at approximately 1000 rpm.
12. Set the thermostat at 32 F (0 C), and run the
unit in cool until the box temperature
approaches 32 F (0 C).
13. Make sure that the unit is running in cool, the
compressor is running at approximately 1000
rpm, the suction pressure is 2 to 8 psig (14 to
55 kPa), and the head pressure is at least
180 psig (1241 kPa) for R-134a systems or
275 psig (1896 kPa) for R-404A systems. If
necessary, raise the head pressure by covering
the condenser grille.
14. With these conditions established, open the
valve on the refrigerant drum to deliver liquid.
15. Observe the suction pressure and slowly open
the low side gauge manifold valve to allow
liquid refrigerant to flow into the compressor
suction service valve.
16. Control the liquid flow so the suction pressure
increases approximately 20 psig (138 kPa).
17. Observe the liquid line sight glass. Close the
valve on the refrigerant drum when the
bubbles disappear from the sight glass or
when the system capacity has been reached
(see unit specifications).
18. Close the low side valve on the gauge
manifold and operate the unit for 15 minutes.
19. Model 20 only.
a. Turn the unit Off and shut off the truck
engine.
48
b. Connect the electric power receptacle to
an appropriate electric power supply. Start
and run the unit in cool on electric
operation for a minimum of 15 minutes.
c. Turn the unit Off and disconnect the
electric power supply. Start the truck and
run the unit in cool on engine operation for
a minimum of 15 minutes.
20. Check the liquid line sight glass for bubbles.
Repeat steps 13 through 20 if bubbles are
visible.
21. Stop the unit, shut off the truck engine and
remove the gauge manifold set.
22. The above conditions MUST be established
each time the refrigerant level is checked, or if
refrigerant needs to be added for any reason.
NOTE: To prevent oil migration from one
compressor to another, and for proper oil
return when a compressor is operating,
operate a compressor for a minimum of 15
minutes. Do not operate a compressor for
shorter intervals.

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. Place a test box over the evaporator.
2. Install gauge manifold set.
3. Run the unit in cool on engine driven
compressor operation until the thermometer
reads 32 F (0 C).
4. Establish head pressure of 180 psi (1241 kPa)
for R-134a systems or 275 psi (1896 kPa) for
R-404A systems. It may be necessary to