Product manual

42 IOMM ACR/AGR-1
System Adjustment
To maintain peak performance at full load operation, the system superheat and liquid subcooling may
require adjustment. Read the following subsections closely to determine if adjustment is required.
Liquid Sightglass and Moisture Indicator
The color of the moisture indicator is an indication of the dryness of the system and is extremely
important when the system has been serviced. Immediately after the system has been opened for
service, the element may indicate a wet condition. It is recommended that the equipment operate for
about 12 hours to allow the system to reach equilibrium before deciding if the system requires a
change of drier cores.
Bubbles in the sightglass at constant full load conditions indicates a shortage of refrigerant, a
plugged filter-drier, or a restriction in the liquid line. However, it is not unusual to see bubbles in the
sightglass during changing load conditions.
Refrigerant Charging
Liquid line subcooling at the liquid shut-off valve should be between 15° and 20°F at full load. If the
unit is at steady full load operation and bubbles are visible in the sightglass, then check liquid
subcooling.
Thermostatic Expansion Valve
The expansion valve performs one specific function. It keeps the evaporator supplied with the proper
amount of refrigerant to satisfy the load conditions.
The sensing bulb of the expansion valve is installed in the closest straight run of suction line from the
evaporator. The bulb is held on by clamps around the suction line and is insulated to reduce the
effect of surrounding ambient temperatures. In case the bulb must be removed, simply slit the
insulation on each side of the bulb, remove the clamps and then remove the capillary tubing that runs
along the suction line from the valve.
The power element is removable from the valve body without removing the valve from the line.
Note: The superheat is factory set and adjustment is not needed unless operation is outside
the 8° to 12°F range.
CAUTION
Before adjusting superheat, check unit charge is correct and liquid line sightglass is
full with no bubbles.
The suction superheat for the suction leaving the evaporator is set at the factory for 8 to 12 degrees F
at full load. To have full rated unit performance the superheat must be about 8 degrees F at 95°F
outdoor ambient temperature.
Crankcase Heaters
The screw compressors are equipped with internal crankcase heaters. The function of the heater is to
keep the temperature in the crankcase high enough to prevent refrigerant from migrating to the
crankcase and condensing in the oil during off-cycle.
Power must be supplied to the heaters 24 hours before starting the compressors.