6-3
T-296
c. Frontseat the suction service valve. The refrigerant
will be trapped between the compressor suction ser-
vice valve and the liquid line valve.
d. Before opening up any part of the system, a slight
positive pressure should be indicated on the pressure
gauge. If a vacuum is indicated, emit refrigerant by
cracking the liquid line valve momentarily to build up a
slight positive pressure.
e. When opening up the refrigerant system, certain
parts may frost. Allow the part to warm to ambient
temperature before dismantling. This avoids internal
condensation which puts moisture in the system.
f. After repairs have been made, be sure to perform a
refrigerant leak check (refer to paragraph 6.5), and
evacuate and dehydrate the low side (refer to para-
graph 6.6).
g. Check refrigerant charge (refer to paragraph 6.7).
6.5 REFRIGERANT LEAK CHECKING
WARNING
Never use air for leak testing. It has been
determined that pressurized, air-rich mix-
tures of refrigerants and air can undergo
combustion when exposed to an ignition
source.
a. 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.
b. If the system is without refrigerant, charge the system
with refrigerant 134a to build up pressure between 2.1
to 3.5 kg/cm
@
(30 to 50 psig). Remove refrigerant cyl-
inder and leak-check all connections.
NOTE
Only refrigerant 134a should be used to pres-
surize the system. Any other gas or vapor will
contaminate the system, which will require
additional purging and evacuation of the sys-
tem.
c. If required, remove refrigerant using a refrigerant
recovery system and repair any leaks.
d. Evacuate and dehydrate the unit. (Refer to paragraph
6.6.)
e. Charge unit per paragraph 6.7.
6.6 EVACUATION AND DEHYDRATION
6.6.1 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.
6.6.2 Preparation
a. Evacuate and dehydrate only after pressure leak test.
(Refer to paragraph 6.5.)
b. Essential tools to properly evacuate and dehydrate
any system include a vacuum pump (8 m
3
/hr = 5 cfm
volume displacement) and an electronic vacuum
gauge. (The pump is available from Carrier Trans-
icold, P/N 07-00176-11.)
c. 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.
d. Additional time may be saved during a complete sys-
tem pump down by replacing the filter-drier with a
section of copper tubing and the appropriate fittings.
Installation of a new drier may be performed during
the charging procedure.
6.6.3 Procedure - Complete system
a. Remove all refrigerant using a refrigerant recovery
system.
b. The recommended method to evacuate and dehy-
drate the system is to connect three evacuation
hoses (see Figure 6-5) to the vacuum pump and
refrigeration unit. Be sure the service hoses are
suited for evacuation purposes.
c. 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.
d. Midseat the refrigerant system service valves.
e. Open the vacuum pump and electronic vacuum
gauge valves, if they are not already open. Start the
vacuum pump. Evacuate unit until the electronic vac-
uum gauge indicates 2000 microns. Close the elec-
tronic vacuum gauge and vacuum pump valves. Shut
off the vacuum pump. Wait a few minutes to be sure
the vacuum holds.
f. Break the vacuum with clean dry refrigerant 134a
gas. Raise system pressure to approximately 0.2 kg/
cm
@
(2 psig), monitoring it with the compound gauge.
g. Remove refrigerant using a refrigerant recovery sys-
tem.
h. Repeat steps e.and f. one time.
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