Table of Contents
Advertisement
P24A & P34A Service Manual
Pumpdown. The function of the pumpdown is to transfer all the liquid refrigerant from the freezer
(evaporator) into the receiver. Pumpdown should only be performed when the freezer is clear of ice.
Its main purposes are:
1. To check the total refrigerant charge.
2. To perform service or repair work on the machine.
3. To winterize the machine.
4. To remove excess water from the ammonia.
5. To prepare the machine for disconnection or moving.
To perform a pumpdown, follow this procedure:
1. With the machine running, close the liquid feed stop valve (58) nearest the receiver.
2. Open the water tank drain valve partially to allow a continuous flow of warm make-up water into
the water tank and still maintain a good level in the tank. An auxiliary supply of warm water (not
to exceed 100°F) may be used if available. Warmer water affords a more complete pumpdown.
3. Allow the machine to operate and complete two freeze and harvest cycles.
4. After the second harvest cycle, stop the machine, throw the electrical disconnect, and lock-out all
power to the machine.
5. Remove wire #17 from the freezer pressure switch (2PS) and insulate the end to prevent a short
circuit.
6. Restore power to the machine and start the water pump only, to circulate warm water through the
freezer.
7. When the suction pressure increases to 70 psig or higher, start the compressor and allow the
machine to stop automatically by the low pressure switch at approximately 15 psig. (Lower
pressure can be obtained by jumping out the pressure switch.) Remove all power from the
machine before opening the control panel cover. With the pressure switch jumped out, the
machine can be manually started and stopped. Do not operate the machine below 2 psig.
8. When the desirable pumpdown is obtained, close the thawing gas stop valve, #90, and the
discharge line stop valve, #55. Other valves may also be closed to isolate a particular area which
may require attention.
9. To perform a total pumpdown, it may be necessary to apply heat directly to the oil trap in order to
boil off the liquid ammonia and oil mixture.
Removal of Ammonia Refrigerant from the Machine. Liquid ammonia can be removed from the
machine through the receiver drain valve, #44. Refer to Sections 1, 2 and Appendix A for special
warnings and instructions regarding the handling of ammonia. Make sure you are familiar with and
technically qualified to handle anhydrous-ammonia refrigerant.
12/18/12
9-17
SERVICING OPERATIONS
Advertisement
Table of Contents
