Evaporator; Refrigerant Charging - McQuay AGZXXXBS Series Installation, Operation And Maintenance Manual

Evaporator

The evaporators are the direct expansion, shell-and-tube type with refrigerant flowing
through the tubes and water flowing through the shell over the tubes or stainless steel
brazed-plate type. The tubes are internally finned to provide extended surface as well
as turbulent flow of refrigeration through the tubes. Other than cleaning and testing, no
service work should be required on the evaporator.

Refrigerant Charging

AGZ air-cooled chillers are shipped factory charged with a full operating charge of
refrigerant but there can be times that a unit must be recharged at the job site. Follow
these recommendations when field charging. Refer to the unit operating charge found
in the Physical Data Tables.
Unit charging can be done at any steady load condition (preferably at 75 to 100% load)
and at any outdoor temperature (preferably higher than 70°F (21.1°C). Unit must be
allowed to run 5 minutes or longer so that the condenser fan staging is stabilized at
normal operating discharge pressure.
condenser fans operating on each refrigerant circuit.
The AGZ units have a condenser coil design with approximately 15% of the coil tubes
located in a subcooler section of the coil to achieve liquid cooling to within 5°F (3°C)
of the outdoor air temperature when all condenser fans are operating. This is equal to
15°F to 20°F (8.3°C to 11.1°C) subcooling below the saturated condensing temperature
when the pressure is read at the liquid valve between the condenser coil and the liquid
line filter-drier. Once the subcooler is filled, extra charge will not lower the liquid
temperature and does not help system capacity or efficiency.
One of the following three scenarios will be experienced with an undercharged
unit:
1. If the unit is slightly undercharged, the unit will show bubbles in the sight glass.
2. If the unit is moderately undercharged, it will normally trip on freeze protection.
3. If the unit is severely undercharged, the unit will trip due to lack of liquid flow to
IOMM AGZ-5
Recharge the unit as described in the charging procedure below.
Recharge the unit as described in the charging procedure below. However,
freezestat trips can also be an indication of low flow or poor heat transfer due to
tube fouling. Anti-freeze solutions can also cause freezestat trips.
the expansion valve. In this case either remove the remaining charge by means of a
proper reclamation system and recharge the unit with the proper amount of
refrigerant as stamped on the unit nameplate, or add refrigerant through the suction
valve on the compressor. If the unit is severely undercharged, the unit can nuisance
trip during this charging procedure. If this happens, operate the unit at minimum
load, adding charge until the sight glass is clear. Once the unit has enough charge
so that it does not trip out, continue with step 2 of the charging procedure below.
AGZ 026B through 130B
For best results, charge with two or more
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