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B – Evacuating the System
IMPORTANT
The compressor should never be used to evacuate
a refrigeration or air conditioning system.
1– Attach gauge manifold. Connect vacuum pump (with
vacuum gauge) to center port of gauge manifold.
With both manifold service valves open, start pump
and evacuate indoor coil and refrigerant lines.
IMPORTANT
A temperature vacuum gauge, mercury vacuum
(U–tube), or thermocouple gauge should be used.
The usual Bourdon tube gauges are not accurate
enough in the vacuum range.
2– Evacuate the system to 29 inches (737mm) vacuum.
During the early stages of evacuation, it is desirable
to stop the vacuum pump at least once to determine
if there is a rapid loss of vacuum. A rapid loss of
vacuum would indicate a leak in the system and a
repeat of the leak testing section would be necessary.
3– After evacuating system to 29 inches (737mm), close
gauge manifold valves to center port, stop vacuum
pump and disconnect from gauge manifold. Attach
an upright nitrogen drum to center port of gauge
manifold and open drum valve slightly to purge line
at manifold. Break vacuum in system with nitrogen
pressure by opening manifold high pressure valve.
Close manifold high pressure valve to center port.
4– Close nitrogen drum valve and disconnect from
gauge manifold center port. Release nitrogen
pressure from system.
5– Connect vacuum pump to gauge manifold center
port. Evacuate system through manifold service
valves until vacuum in system does not rise above
29.7 inches (754mm) mercury (5mm absolute
pressure) within a 20–minute period after stopping
vacuum pump.
6– After evacuation is complete, close manifold center
port, and connect refrigerant drum. Pressurize
system slightly with refrigerant to break vacuum.
C – Leak Testing (To Be Done Only After
Pump Down)
1– Attach gauge manifold and connect a drum of dry
nitrogen to center port of gauge manifold.
2– Open high pressure valve on gauge manifold and
pressurize line set /indoor coil to 150 psig (1034 kPa).
3– Check lines and connections for leaks.
4– Release nitrogen pressure from the system,
correct any leaks and recheck.
CAUTION
When using dry nitrogen, a pressure reducing
regulator must be used to prevent excessive
pressure in gauge manifold, connecting hoses, and
within the system. Regulator setting must not
exceed 150 psig (1034 kpa). Failure to use a regulator
can cause equipment failure resulting in injury.
NOTE-If electronic leak detector is used, add a trace of
refrigerant to the nitrogen for detection by the leak
detector.
D – Charging
Charging must be done in the cooling mode. If system
is completely void of refrigerant, the recommended and
most accurate method of charging is to weigh the
refrigerant into the unit according to the total amount
shown on the unit nameplate.
If weighing facilities are not available or if unit is just
low on charge, the following procedure applies. RFC
and TXV systems use different charging methods.
Separate discharge and vapor line service ports are
provided outside the unit for connection of gauge
manifold during charging procedure as well as a
suction line service port.
1 – Expansion Valve Systems
The following procedures are intended as a general
guide for use with expansion valve systems only. For
best results, indoor temperature should be between 70
°
F
and 80
°
F. If outdoor temperature is 60
°
F (16
°
C) or above
the approach method of charging is used. If outdoor
temperature is less than 60
°
F (16
°
C) the subcooling
method of charging is used. Slight variations in charging
temperature and pressure should be expected. Large
variations may indicate a need for further servicing.
IMPORTANT
The following procedures require accurate
readings of ambient (outdoor) temperature, liquid
temperature and liquid pressure for proper
charging. Use a thermometer with accuracy of +2
°
F and a pressure gauge with accuracy of +5 PSIG.
APPROACH METHOD (TXV SYSTEMS)
(Ambient Temperature of 60
F [16
C] or Above)
1 – Connect gauge manifold. Connect an upright
R–22 drum to center port of gauge manifold.
2 – Record outdoor air (ambient) temperature.
3 – Operate indoor and outdoor units in cooling
mode. Allow outdoor unit to run until system
pressures stabilize.
4 – Make sure thermometer well is filled with
mineral oil before checking liquid line
temperature.
