Dometic DX Remote & Self-Contained A/C, Инструкция по установке и эксплуатации

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L-2086
New A/C units are available from the factory with non-HCFC refrigerants.
R-417A (also known as NU-22
® or Isceon 59 ® ) is a direct drop-in replace-
ment for R22. It will work with Alkyl Benzene and mineral lubricants so
standard compressors can be used. Note that some self-contained units
(with rotary compressors) and chillers (with scroll compressors) might have
R-407C with POE lubricant.
Both R-417A and R-407C are blended refrigerants, meaning they are made
up from multiple component refrigerants. In most cases the user will not
notice a change in operation or performance of these systems, but charging
a system with a
blend requires some special considerations.
• We currently don’t have charging curves for either gas. A system with a
blend must be charged by superheat.
• The system should be charged with liquid refrigerant from the tank to
prevent fractionation. Note that some tanks have a dip tube so the tank
is used in the upright position, while other tanks will need to be turned
upside down to get liquid. This should be clearly marked on the tank.
• A partial leak in the system doesn’t necessarily mean that the refrigerant
needs to be removed and recharged. However, it is possible that enough
fractionation can occur that would require a complete evacuation and
recharge. This will be evident when trying to charge the system and the
temperature/pressures will not respond correctly.
To charge a split system with a blend:
1. Evacuate lines and evaporator (cooling unit) as normal.
2. Open base valves to release the refrigerant in the condensing unit.
3. Attach an accurate thermometer or temperature sensor to the suction
line near the base valve, at the 3 or 9 o’clock position on the line. Insu-
late over the sensor so that the ambient temperature does not affect the
reading.
4. Open the suction base valve to the test position. The low-side gauge
should now register a pressure reading.
5. Turn on the system in the cooling mode, and set the thermostat to a low
setting so the unit will stay on.
6. Allow the system to run for five minutes so the pressures will stabilize,
then measure the superheat. This must be done using the Dew Point for
conversion.
Note: There is no ideal superheat temperature. It should be in the range
of 10° to 20°F (5.6° to 11.1°C), depending on the heat load. On cool
days, superheat will be lower, and on hot days it will be higher.
7. To reduce superheat, slowly add liquid refrigerant to the suction line. Do
this in very small increments and allow the system to stabilize before
taking another reading. DO NOT OVERCHARGE! If the system is
overcharged, refrigerant must be removed from the liquid line, using an
approved recovery cylinder.
Warning: You are charging with liquid refrigerant. To prevent liquid from
“slugging” the compressor, open the manifold valve only a small amount
to allow the refrigerant to flash from liquid to vapor in the charging hose.
GO SLOWLY! A special valve is available for charging liquids.
8. Once the superheat is set properly, close the manifold gauge valves,
and backseat the discharge base valve. Tighten the stem packing nuts,
remove manifold gauges, and replace service port caps.
Glossary
Blend - A refrigerant that is made up of two or more single-component
refrigerants.
Fractionation - Change in the composition of a blend because one (or
more) of the component refrigerants is lost (or removed faster than the
others). This happens because the components have different boiling
points. It can occur in a tank or system that has lost gas, or locally in a
system component such as a coil or accumulator.
Temperature Glide - Because of the different boiling temperatures of
the components, a blend will evaporate over a range of temperatures
(at a constant pressure). The difference between the Bubble Point and
the Dew Point is the Temperature Glide.
Superheat - The “extra” heat (beyond what is required to fully evap-
orate the refrigerant) that the refrigerant picks up in the evaporator.
Superheat is determined by measuring the refrigerant temperature (at
the suction line) and then subtracting the saturation temperature (found
from the pressure-temperature chart using suction pressure). Use the
Dew Point pressure for blends.
Bubble Point - The pressure at which a blend starts to boil. Listed in
the pressure-temperature chart.
Dew Point - The pressure at which a blend finishes boiling. Listed in
the pressure-temperature chart.
Fig. 34 Charging Systems with Alternative Refrigerants