4-4
T-312
4.5 REFRIGERANT LEAK CHECK
A refrigerant leak check should always be performed
after the system has been opened to replace or repair a
component.
To check for leaks in the refrigeration system, perform
the following procedure:
NOTE
It must be emphasized that only the correct
refrigerant drum should be connected to
pressurize the system. Any other gas or
vapor will contaminate the system, which will
require additional evacuation.
a. Ensure all the service valves and solenoid valves are
open. It will be necessary to energize the solenoid
valves from an external power source.
b. If the system is without refrigerant, charge the system
with refrigerant vapor to build up pressure between 30
to 50 psig
(2.74 to 3.40 BAR)
.
c. Add sufficient nitrogen to raise system pressure to a
maximum of 150 psig
(10.21 BAR)
.
d. Check for leaks. It is recommended that an electronic
leak detector be used to find refrigerant leaks in a
system. Testing joints with soapsuds is satisfactory
and may be necessary under conditions when an
electronic leak detector will not function correctly.
e. Remove refrigerant from system and repair any
leaks.
f. Evacuate and dehydrate the system. (Refer to
paragraph 4.6)
g. Charge the unit. (Refer to paragraph 4.7)
h. Ensure that self-test has been performed and that
there are no errors or alarms indicated. (Refer to
paragraphs 2.1.5 and 2.1.6)
4.6 EVACUATION AND DEHYDRATION
4.6.1 General
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.
4.6.2 Preparation
NOTE
1. Using a compound gauge for
determination of vacuum level is not
recommended because of its inherent
inaccuracy.
2. Never evacuate an open drive
compressor below 500 microns.
a. Evacuate and dehydrate only after pressure leak test.
(Refer to paragraph 4.5)
b. Essential tools to properly evacuate and dehydrate
any system include a good vacuum pump with a
minimum of 6 cfm
(10.2 m
3
/hr)
volume displacement,
(CTD P/N 07-00176-11), and a good digital (micron)
vacuum indicator (CTD P/N 07--00414--00).
c. Keep the ambient temperature above 60
_
F
(15.6
_
C)
to speed evaporation of moisture. If ambient
temperature is lower than 60
_
F
(15.6
_
C)
, ice may
form before moisture removal is complete. It may be
necessary to use heater blankets, heat lamps or
alternate sources of heat to raise system
temperature.
4.6.3 Procedure for Evacuation and Dehydrating
System
a. Remove refrigerant using a refrigerant recovery
system. (CTD P/N MVS--115--F--L--CT for 115 volt
power source or CTD P/N MVS--240--F--L--CT for 240
volt power source)
b. The recommended method is connecting two lines
(3/8” OD copper tubing or refrigerant hoses designed
for vacuum service) to the manifold guage set. Attach
one line to the condenser service (King) valve and the
other line to the evaporator service port. (See
Figure 4-4)
c. Connect lines to unit and manifold and make sure
vacuum gauge valve is closed and vacuum pump
valve is open.
d. To speed up evacuation time, open solenoid valves
electrically. An additional vacuum pump may be
added and connected to the compressor suction
service port. (See Figure 4-4)
e. Start vacuum pump. Slowly open valves halfway and
then open vacuum gauge valve.
f. Evacuate unit until vacuum gauge indicates 1500
microns vacuum. Close gauge valve, vacuum pump
valve, and stop vacuum pump.
g. Break the vacuum with clean dry refrigerant or dry
nitrogen. Use the refrigerant that the unit calls for.
Raise system pressure to approximately 2 psig
(0.14
BAR)
.
h. Remove refrigerant using a refrigerant recovery
system, or if using nitrogen vent to atmosphere.
i. Start vacuum pump and open all valves. Evacuate
unit to 500 microns vacuum.
j. Close off pump valve, isolate vacuum gauge in
system and stop pump. Wait five minutes to see if
vacuum holds.
k. With a vacuum still in the unit, the refrigerant charge
may be drawn into the system from a refrigerant
container on weight scales. (Refer to paragraph 4.7)
