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Once all of the piping connections are complete, leak test
the unit and then pull a deep dehydration vacuum. Connect the
vacuum pump to the low side and high side of the system. For
best results, it is recommended that a vacuum of at least 500
microns (0.5 mm Hg) be obtained. Afterwards, to ensure that
no moisture is present in the system, perform a standing vacu-
um-rise test.
With the unit in deep vacuum (500 microns or less), isolate
the vacuum pump from the system. Observe the rate-of-rise of
the vacuum in the system. If the vacuum rises by more than
50 microns in a 30-minute time period, then continue the dehy-
dration process. Maintain a vacuum on the system until the
standing vacuum requirement is met. This will ensure a dry
system.
By following these evacuation and dehydration procedures,
the amount of moisture present in the system will be mini-
mized. It is required that liquid line filter driers be installed be-
tween the condenser(s) and the expansion devices to capture
any foreign debris and provide additional moisture removal ca-
pacity. Be sure to consider the pressure drop of the filter drier
when determining piping requirements.
REFRIGERANT LINE SIZING — Sizing depends on length
of lines between various sections of the refrigerant system. See
Tables 2-6 for pipe connection details. Consider the amount of
liquid lift and drop in the system as well as proper compressor
oil return. See Liquid Lift section for more information. Con-
sult Carrier System Design Manual, Part 3, or Carrier E20-II
Refrigerant Piping Computer Program for proper piping sizes
and design.
PRESSURE RELIEF — The ASHRAE Standard 15, Safety
Code for Mechanical Refrigeration states: “Every refrigerat-
ing system shall be protected by a pressure relief device or
some other means designed to safely relieve pressure due to
fire or other abnormal conditions.” The 09DP units are pro-
vided with a 210 F temperature fusible plug on the liquid line
of each circuit. This may or may not meet local code require-
ments.
REFRIGERANT RECEIVER — A refrigerant receiver is
not
furnished with 09DP units and is
not
recommended for normal
applications as its use will be detrimental to the desired effects
of subcooling. However, if a particular application requires a
receiver to increase refrigerant holding capacity of the con-
denser, a receiver can be used. Recommended receiver and
valve installation and piping are shown in Fig. 18. When a
receiver is to be used year-round, it should be installed indoors.
Procedure for Using the Refrigerant Receiver (Fig. 18)
1.
During normal operation —
Valve A is open and valves
B and C are closed. Receiver is isolated from the system.
2.
For servicing —
Valves A and C are closed and valve B is
open. Run unit until all the refrigerant is in the receiver
and then close valve B. Unit is now ready for servicing.
3.
To resume operation —
Leave valve A closed and open
valves B and C. Run unit until the stored refrigerant is
drawn into the system. To completely remove the refrig-
erant from the receiver, throttle valve B while noting con-
dition of refrigerant in the liquid line sight glass; also,
watch the suction pressure. A sudden surge of bubbles in
the sight glass and a rapid decrease in suction pressure
indicate that all the refrigerant has been withdrawn from
the receiver. Immediately close valves B and C and then
open valve A. The unit should now be ready for normal
operation, with the receiver isolated from the system.
The
system should be charged to a clear sight glass when un-
der normal operation.
LIQUID LIFT — Amount of liquid lift available before refrig-
erant flashing occurs depends on amount of liquid sub-cooling
in the system.
All 09DP condensers have positive subcooling when ap-
plied with optimum charge. With subcooling, it is possible to
overcome an appreciable pressure drop and/or static head (due
to elevation of the liquid metering device above the condenser).
When 09DP condensers are applied with minimum charge,
they do not provide positive subcooling. If subcooling is re-
quired, it must be obtained by external means such as a liquid
suction interchanger.
The average amount of liquid lift available is shown in
Tables 7 and 8 for refrigerants R-410A and R-134a. It is rec-
ommended that the evaporator be at the same level as the con-
denser, or lower.
LEGEND
SAE —
Society of Automotive Engineers
Fig. 16 — Fan Cycle Pressure Switch
a9-
248tf.tif
TUBING
PACKAGE
Fig. 17 — Tubing Package Installed in Unit
WARNING
Do not apply pumpdown cycle with MCHX (microchannel
heat exchanger) condensers. Damage to unit or personal
injury may occur.
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