Operating instructions

Remote Evaporator (AGZ-BM Only)
The evaporator is the direct expansion, shell-and-tube type with refrigerant flowing through the tubes
and water flowing through the shell over the tubes. The tubes are internally finned to provide
extended surface as well as turbulent flow of refrigeration through the tubes. Models AGZ 070BM
or smaller have a stainless steel brazed-plate type evaporator. Other than cleaning and testing, no
service work should be required on the evaporator.
Refrigerant Charging
Units are shipped with a holding charge of refrigerant and the system must be charged 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. For
best results charge with two or more condenser fans operating on each refrigerant circuit.
The ACZ/AGZ units have a condenser coil design with approximately 15% of the coil tubes located
in a subcooler section of the coil. This results in liquid cooling to within 5°F (3°C) of the outdoor air
temperature when all condenser fans are operating. This is equal to about 15°F-20°F (8.3°C-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. Recharge the
unit as described in the charging procedure below.
2. .If the unit is moderately undercharged, it will normally trip on freeze protection. 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 in the system evaporator.
3. If the unit is severely undercharged, the unit will trip due to lack of liquid flow to 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.
Procedure to charge a moderately undercharged ACZ/AGZ unit:
1. If a unit is low on refrigerant, you must first determine the cause before attempting to recharge
the unit. Locate and repair any refrigerant leak. Evidence of oil is a good indicator of leakage,
however, oil can not be visible at all leaks. Liquid leak detector fluids work well to show
bubbles at medium sized leaks, but electronic leak detectors can be needed to locate small leaks.
2. Add the charge to the system through the suction shutoff valve or through the Schrader fitting on
the tube entering the evaporator between the compressor and the evaporator head.
3. The charge can be added at any load condition between 25-100% load per circuit but at least two
fans should be operating per refrigerant circuit if possible. The suction superheat should be in
the 8 to 12 degree F (4.4°C - 6.6°C) range.
4. Add sufficient charge to clear the liquid line sight glass and until all flashing stops in the sight
glass.
IMM ACZ/AGZ-4 ACZ / AGZ-BM 67