Operating instructions

62 IMM AGSB-60
1. On the circuit controller, under the "SET EXV SPs (2)", change the "Service Pumpdown"
set point from "No" to "Yes".
2. If the circuit status is "Off:PumpDwnSw", move the circuit pumpdown switch from
"Pumpdown and Stop" to "Auto". Also clear the anticycle timers through the MicroTech
keypad.
3. Move the circuit switch to the OFF position. The compressor will unload to minimum
slide position and the unit will pump down.
4. Upon completing the full pumpdown per step 3, the "Service Pumpdown" setpoint is
automatically changed back to "No" which reverts back to standard 25 psig (172 kPa)
pumpdown stop pressure.
5. If the pumpdown does not go to 15 psig (103 kPa) on the first attempt, one more attempt
can be made by repeating the above steps. Do not repeat "Service Pumpdown" more than
once to avoid excessive screw temperature rise under this abnormal condition.
6. The circuit is now in the deepest pumpdown that can be achieved by the use of the
compressor. Close the two liquid line shutoff valves upstream of the filter-drier, on the
circuit to be serviced plus the optional suction shutoff valve. Manually open the EXV,
then pump the remaining refrigerant from the evaporator. Any remaining refrigerant must
be removed from the circuit by the use of a refrigerant recovery unit.
7. Loosen the cover bolts, remove the cap and replace the filters.
8. Evacuate and open valves.
Evacuate the lines through the liquid line manual shutoff valve(s) to remove noncondensables
that can have entered during filter replacement. A leak check is recommended before returning
the unit to operation.
Compressor Slide Valves
The slide valves used for unloading the compressor are hydraulically actuated by pulses from
the load/unload solenoid as controlled by the circuit controller. See OM AGS for details on
the operation.
Electronic Expansion Valve
The electronic expansion valve is located in the liquid line entering the evaporator.
The expansion valve meters the amount of refrigerant entering the evaporator to match the
cooling load. It does this by maintaining constant condenser subcooling. (Subcooling is the
difference between the actual refrigerant temperature of the liquid as it leaves the condenser
and the saturation temperature corresponding to the liquid line pressure.) All AGS chillers are
factory set at 20 degrees F subcooling at 100% slide position and approximately 5 degrees F
subcooling at minimum slide position. The controller will offset these settings based on
discharge superheat.
When the control panel is first powered, the microprocessor will automatically step the valve
to the fully closed (shut) position. The valve will take approximately 30 seconds to go from a
full open position to a full closed position.
The position of the valve can be viewed at any time by using the MicroTech II controller
keypad through the View Refrigerant menus. There are 6386 steps between closed and full
open. There is also a sight glass on the EXV to observe valve movement.
Evaporator
The evaporator is a flooded, shell-and-tube type with water flowing through the tubes and
refrigerant flowing up the shell over the tubes. The tubes are internally enhanced to provide