Carrier 69NT40-541-306, Операция и обслуживание

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7–5 T-354
5. When opening up the refrigerant system, certain parts may frost. Allow the part to warm to ambient tempera-
ture before dismantling. This avoids internal condensation, which puts moisture in the system.
6. After repairs have been made, be sure to perform a refrigerant leak check (refer to Section 7.5 ), and evac-
uate and dehydrate the low side ( Section 7.6 ).
7. Check refrigerant charge (refer to Section 7.7 ).
7.5 REFRIGERANT LEAK CHECKING
WARNING
!
Never use air for leak testing. It has been determined that pressurized, air-rich mixtures of
refrigerants and air can undergo combustion when exposed to an ignition source.
1. The recommended procedure for finding leaks in a system is with a R-134a electronic leak detector. Testing
joints with soapsuds is satisfactory only for locating large leaks.
2. If the system is without refrigerant, charge the system with refrigerant 134a to build up pressure between 2.1
to 3.5kg/cm

(30 to 50psig). Remove refrigerant cylinder and leak-check all connections.
NOTE
Only refrigerant 134a should be used to pressurize the system. Any other gas or vapor will contami-
nate the system, which will require additional purging and evacuation of the system.
3. If required, remove refrigerant using a refrigerant recovery system and repair any leaks.
4. Evacuate and dehydrate the unit (refer to Section 7.6 ).
5. Charge unit per Section 7.7 .
7.6 EVACUATION AND DEHYDRATION
7.6.1 General
Moisture is the deadly enemy of refrigeration systems. The presence of moisture in a refrigeration system can have
many undesirable effects. The most common are copper plating, acid sludge formation, “freezing-up” of metering
devices by free water, and formation of acids, resulting in metal corrosion.
7.6.2 Preparation
1. Evacuate and dehydrate only after pressure leak test (refer to Section 7.5 ).
2. Essential tools to properly evacuate and dehydrate any system include a vacuum pump (8m

/hr = 5cfm vol-
ume displacement) and an electronic vacuum gauge. The pump is available from Carrier Transicold (P/N
07-00176-11).
3. If possible, keep the ambient temperature above 15.6
°
C (60
°
F) to speed evaporation of moisture. If the
ambient temperature is lower than 15.6
°
C (60
°
F), ice might form before moisture removal is complete. Heat
lamps or alternate sources of heat may be used to raise the system temperature.
4. Additional time may be saved during a complete system pump down by replacing the filter-drier with a sec-
tion of copper tubing and the appropriate fittings. Installation of a new drier may be performed during the
charging procedure.
7.6.3 Procedure - Complete System
1. Remove all refrigerant using a refrigerant recovery system.
2. The recommended method to evacuate and dehydrate the system is to connect three evacuation hoses
(see Figure 7.5 ) to the vacuum pump and refrigeration unit. Be sure the service hoses are suited for evacu-
ation purposes.
3. Test the evacuation setup for leaks by backseating the unit service valves and drawing a deep vacuum with
the vacuum pump and gauge valves open. Shut off the pump and check to see if the vacuum holds. Repair
leaks if necessary.
4. Midseat the refrigerant system service valves.