6--6
T-334
valve is more than 10% open at controller function code
Cd01. The suction modulating valve may be opened by
use of the controller function code Cd41 valve override
control (refer to paragraph 6.20).
Remove refrigerant cylinder and leak-check all
connections.
If required, remove refrigerant using a refrigerant
recovery system and repair any leaks
Evacuate, dehydrate and charge the unit in accordance
with the following paragraphs
6.4.4 Evacuation and Dehydration
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.
Preparation
Evacuate and dehydrate only after pressure leak test.
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 Transicold, part number
07-00176-11.)
Additional time may be saved during a complete system
pump down by replacing the filter drier with a section of
copper tubing.
Procedure
a. Remove all refrigerant using a refrigerant recovery
system. Refer to section 6.4.2.
b. The recommended method to evacuate and dehy-
drate the system is to connect evacuation hoses at
the liquid, economizer and suction access val-
ves.(see Figure 6-6). Be sure the service hoses are
suited for evacuation purposes.
c. The area between the suction modulating valve and
evaporator expansion valve may not be open to the
access valves. To ensure evacuation of this area,
check that the suction modulating valve is more than
10% open at controller function code Cd01. If re-
quired, the suction modulating valve may be opened
by use of the controller function code Cd41 valve
override control.
d. Test the evacuation setup for leaks 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.
e. If possible, keep the ambient temperature above
15.6C (60F) to speed evaporation of moisture. If the
ambient temperature is lower than 15.6C (60F), ice
might form before moisture removal is complete.
Heat lamps or alternate sources of heat may be used
to raise the system temperature.
f. 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.
g. Break the vacuum with clean dry refrigerant 134a gas.
Raise system pressure to approximately 0.2 kg/cm
2
(2 psig), monitoring it with the compound gauge.
h. Remove refrigerant using a refrigerant recovery sys-
tem.
i. Repeat steps f.and g. one time.
j. Remove the copper tubing and change the filter drier.
Evacuate unit to 500 microns. Close the electronic
vacuum gauge and vacuum pump valves. Shut off the
vacuum pump. Wait five minutes to see if vacuum
holds. This procedure checks for residual moisture
and/or leaks.
k. With a vacuum still in the unit, the refrigerant charge
may be drawn into the system from a refrigerant con-
tainer on weight scales.
6.4.5 Refrigerant Charge
Checking the Refrigerant Charge
NOTE
To avoid damage to the earth’s ozone layer, use
a refrigerant recovery system whenever remov-
ing refrigerant. When working with refrigerants
you must comply with all local government envi-
ronmental laws. In the U.S.A., refer to EPA Sec-
tion 608.
a. Connect the gauge manifold to the liquid and suction
access valves. For units operating on a water cooled
condenser, change over to air cooled operation.
b. Bring the container temperature to approximately 0C
(32F) or below. Then set the controller set point to
-25C (-13F) to ensure that the suction modulation
valve is fully open. Also, check function code Cd21.
The economizer valve should be open. If ambient is
between 16C (60F) and 49C (120F), proceed to step
d.
c. If ambient is below 16C (60F), partially block the con-
denser coil inlet air. Increase the area blocked until
the compressor discharge pressure is raised to
approximately 13 kg/cm
2
(185 psig).
d. On units equipped with a receiver, the level should be
between the glasses. On units equipped with a water
cooled condenser, the level should be at the center of
the glass. If the refrigerant level is not correct, contin-
ue with the following paragraphs to add or remove re-
frigerant as required.
6.4.6 Adding Refrigerant to System (Full Charge)
a. Evacuate unit and leave in deep vacuum.
b. Place cylinder of R-134a on scale and connect charg-
ing line from cylinder to liquid line valve. Purge charg-
ing line at liquid line valve and then note weight of cyl-
inder and refrigerant.
c. Open liquid valve on cylinder and allow the liquid
refrigerant to flow into the unit until the correct amount
of refrigerant has been added.
d. Close liquid valve on cylinder.
e. Start unit in cooling mode. Run approximately 10 min-
utes and check the refrigerant charge.
f. On units equipped with a receiver, the level should be
between the glasses. On units equipped with a water
cooled condenser, the level should be at the center of
the glass. If the refrigerant level is not correct, go to
section 6.4.7.
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