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8.6.7 Evacuation and Dehydration
Moisture is detrimental to refrigerant systems. The presence of moisture in a refrigeration system can have many
undesirable effects such as: copper plating, acid sludge formation, “freeze-up” of the expansion valve, and forma-
tion of acids, resulting in metal corrosion. Proper evacuation of the system will remove any moisture from inside the
system.
NOTES
• Essential tools to properly evacuate any system include a good vacuum pump (5 cfm/8m
3
H volume dis-
placement, Carrier Transicold P/N 07-00176-11) and a good vacuum indicator such as a digital vacuum
gauge (micrometer). Carrier Transicold P/N 07-00414-00.
• The use of a compound gauge is not recommended for use in determining when the evacuation process is
completed because of its inherent inaccuracy.
• Standard service hoses are not recommended for evacuation purposes. Evacuation hoses are recom-
mended for this procedure.
8.6.7.1 Evacuation of Complete System
1. Evacuate only after leak check. (Refer to Section 8.6.6.)
2. If possible keep the temperature of the major components (condenser, evaporator, compressor and
receiver) above 60°F (15.6°C) to speed evaporation of moisture. If the temperature is lower than 60°F
(15.6°C), ice might form before moisture removal is complete. Heat lamps, heat guns or alternate sources of
heat may be used to raise temperature.
3. The recommended method to evacuate the system is to connect three evacuation hoses with vacuum pump
and vacuum indicator (see Figure 8.15).
4. Ensure that the operator message panel displays “RECOVER/LEAK CHK/EVAC MODE” during the
evacuation and dehydration procedures. (Refer to Section 5.2.5.) If the control system switches to Charge
mode during the process, switch it back to the “RECOVER/LEAK CHK/EVAC MODE”.
5. Backseat (turn counter-clockwise) the liquid line service valve, suction service and discharge service valves.
6. With the unit service valves closed (back seated) and the vacuum pump and vacuum indicator valves open,
start the pump and draw a deep vacuum. Shut off the pump and check to see if the vacuum holds. This
operation is to test the evacuation setup for leaks. Repair if necessary.
7. Midseat the refrigerant system service valves and install the service valve caps. Ensure that the operator
message panel displays “RECOVER/LEAK CHK/ EVAC MODE”.
NOTE
The service valve caps help minimize leakage through valve stems during midseat operation.
8. Start the vacuum pump. Evacuate unit until the vacuum indicator indicates 2000 microns. Close the vacuum
pump valve and shut off the pump. Wait a few minutes to ensure the vacuum holds.
9. Break the vacuum with dry nitrogen through the discharge service valve. Raise system pressure to
approximately 2 psig (0.1 bar). Ensure that the control system does not switch to the Charge mode. If this
occurs, switch it back to the “RECOVER/LEAK CHK/EVAC MODE” (Refer to Section 5.2.5)
10. Purge nitrogen from system at the suction service valve.
11. Open the vacuum pump valve and start the pump. Evacuate unit to 500 microns. Close the vacuum pump
valve and shut off the pump. Wait a few minutes to be sure the vacuum holds below 2000 microns.
12. If vacuum holds below 2000 microns continue to step 14. If vacuum rises above 2000 microns continue to
step 13.
13. Repeat steps 8 through 11 until the vacuum stays below 2000 microns.
14. Once the system holds a good vacuum, it is ready to be charged with refrigerant. Refer to Section 8.6.2.
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