IV. CAPACITY CONTROL (576B120 Only)
A suction
A. Control Set Point
The control set point (cylinder load point) is adjustable from 0 to 85 psig. To adjust, turn control set point adjustment nut (Fig. 12) clockwise to its bottom stop. In this position, set point is 85 psig. Then, turn adjustment counterclockwise to desired control set point. Every full turn counterclockwise decreases set point by 7.5 psig.
B. Pressure Differential
The pressure differential (difference between cylinder load and unload points) is adjustable from 6 to 22 psig. To adjust, turn pressure differential adjustment screw (Fig. 12) coun- terclockwise to its back stop position. In this position, differ- ential is 6 psig. Then, turn adjustment screw clockwise to desired pressure differential. Every full turn clockwise increases differential by 1.5 psig.
Fig. 12 — Compressor Capacity Control Unloader
V. COMPRESSOR REMOVAL
See Table 1 for compressor information.
Follow safety codes and wear safety glasses and work gloves.
1.Shut off power to unit and install lockout. Remove unit access panel (front of unit).
2.Remove refrigerant from system using refrigerant removal methods described in GTAC II, Module 5, Charging, Recovery, Recycling, and Reclamation.
3.Disconnect compressor wiring at compressor termi- nal box.
4.Remove bolts from suction flange and discharge ser- vice valve (576B units).
CAUTION: Excessive movement of copper lines at compressor may cause higher levels of vibration when unit is restored to service.
5.Remove crankcase heater from compressor base (576B units only).
6.Remove compressor holddown bolts.
7.Remove compressor from unit.
8.Clean system. Add new liquid line filter drier.
9.Install new compressor in unit.
10.Connect suction and discharge lines to compressor. Ensure that compressor holddown bolts are in place.
11.Install crankcase heater.
12.Connect wiring.
13.Evacuate and recharge unit, per Step VII.
14.Restore unit power.
VI. CRANKCASE HEATER
The crankcase heater prevents refrigerant migration and compressor oil dilution during shutdown when compressor is not operating.
Close both compressor service valves if applicable when crankcase heater is deenergized for more than 6 hours.
VII. REFRIGERANT CHARGE
Unit panels must be in place when unit is operating during charging procedure. Unit is shipped with a holding charge only. Weigh in 7 lbs of
See Troubleshooting Guide on page 13 for additional information.
A. Low Charge Cooling
Using Cooling Charging Charts, Fig. 13 and 14, vary refrig- erant until the conditions of the appropriate chart are met. Note the charging charts are different from type normally used. The charts are based on charging the units to the cor- rect
Connect the pressure gage to the service port on the liquid line service valve. Mount the temperature sensing device on the liquid line, close the liquid line service valve, and insu- late it so that outdoor ambient temperature does not affect the reading.
Operate unit a minimum of 15 minutes. Ensure that temper- ature and pressure have stabilized. Plot liquid pressure and temperature on chart and add or reduce charge as required. Do not vent refrigerant to the atmosphere. Recover any excess charge. Operate the unit until the system stabilizes. Adjust charge to conform with charging chart, using liquid pressure and temperature to read chart.
B. Refrigerant Leaks
Proceed as follows to repair a refrigerant leak and to charge the unit:
1.Locate the leak and ensure that refrigerant system pressure has been relieved.
2.Repair leak following accepted practices.
NOTE: Install a new filter drier in the liquid line whenever the system has been opened for repair.
3.Add a small charge of
4.Evacuate refrigerant system up to 500 micons. If additional leaks are not found.
5.Charge unit with
NOTE: Do not vent refrigerant to the atmosphere. Recover any excess charge.
