6-3
T -309
gauge. If a vacuum is indicated, emit refrigerant by
crackingtheliquidlinevalvemomentarilytobuildup
a slight positive pressure.
g. Whenopeninguptherefrigerantsystem,certainparts
mayfrost.Allowtheparttowarmtoambienttemper-
ature before dismantling. This avoids internal con-
densation which puts moisture in the system.
h. 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).
i. Check refrigerant char ge (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
systemiswithaR-134aelectronicleakdetector.Test-
ingjointswithsoapsudsissatisfactoryonlyforlocat-
ing large leaks.
b. Ifthesystemiswithoutrefrigerant,chargethesystem
with refrigerant 134a to build up pressure between
2.1to3.5kg/cm@(30to50psig).Toensurecomplete
pressurization of the system, refrigerant should be
charged at the compressor suction and economizer
servicevalvesandtheliquidlineservicevalve.Also,
the area between the suction m odulating valve and
evaporatorexpansionvalvemaynot beopentothese
charging points. Pressurebetweenthesecomponents
maybechecked atthelowsideaccessvalve(item1 1,
Figure 2-2) or by checking t hat the suctionmodulat-
ing valve is more than 10% open at controller func-
tion code Cd01. The suction modulating valve may
beopenedbyuseofthecontrollerfunctioncodeCd41
valve override control (refer to paragraph 6.19). Re-
moverefrigerantcylinderandleak-checkallconnec-
tions.
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. Evacuateanddehydratethe unit. (Refertoparagraph
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 devicesby free water, and formation of acids,
resulting in metal corrosion.
6.6.2 Preparation
a. Evacuate and dehydrateonly afterpressure leaktest.
(Refer to paragraph 6.5.)
b. Essential tools to properly evacuate and dehydrate
anysystemincludeavacuumpump(8 m
3
/hr= 5cfm
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 l ower than 15.6_C
(60_F), ice might form before moisture removal is
complete.Heatlampsoralternatesourcesofheatmay
be used to raise the system temperature.
d. Additionaltimemaybesavedduringacompletesys-
tem pump down by replaceing the filter-drier with a
sectionof coppert ubing and the appropriate fittings.
Installation of a new drier may be performed during
the charging procedure.
6
4
5
D
S
2
3
11
9
10
1
7
8
1. Liquid Service Valve
2. Receiver or Water
Cooled Condenser
3. Compressor
4. Discharge Service
Valve
5. Economizer Service
Valve
6. Suction Service Valve
7. Vacuum Pump
8. Electronic Vacuum
Gauge
9. Manifold Gauge Set
10. Refrigerant Cylinder
11. Reclaimer
Figure 6-5. Refrigeration System Service
Connections
6.6.3 Procedure - Complete system
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