CHARGING and START-UP
The control circuit should be energized 24 hours before charging and start-up to open the liquid line solenoid and turn on the crankcase heater. This will assist the evacuation and dehydration process and provide additional compressor protection during the charging and start-up.
Charge refrigerant into a system through a filterdrier in the charging line. This provides further assurance the refrigerant charge is clean and dry. The system refrigerant capacity is approximately 80% of the condenser, receiver, and liquid line capacity. If the condenser volume or refrigerant capacity is unknown, the system refrigerant capacity is often calculated at 90% of the receiver and liquid line capacity. Be cautious if the calculated charge is exceeded. Weigh the refrigerant. The actual refrigerant charge should be less than the calculated capacity. DO NOT charge liquid refrigerant into the suction side of the compressor.
Be sure the compressor discharge valve is open. The suction valve should be open 2 or 3 turns, with a valve stem wrench attached for quick throttle adjusting. High and low pressure gauges should be attached. Liquid charging is faster.
If R-404A or R-507 is used, liquid charging is mandatory. R-404A and R-507 refrigerant cylinders have a dip tube and liquid is charged with the cylinder upright. Break the final vacuum by charging liquid refrigerant into the receiver outlet valve access or the area of liquid line downstream from the receiver outlet.
Approximately 50 to 60% of the system charge can usually be injected into the receiver area before it is necessary to start the compressor for the system to accept more refrigerant . It may be necessary to throttle the compressor suction valve to keep suction pressures reasonable and prevent tripouts during charging and pull-down. If it is necessary to add liquid refrigerant to the suction side, a full control ball valve must be used in the charging line to slowly meter refrigerant vapor into the system.
If the condensing temperature is 105°F or greater, charge the system until the sight glass just clears, being careful not overcharge. If the condensing temperature is below 105°F, a part of the condenser coil can be blocked to raise the condensing temperature to 105°F. Be careful not
to block the air blast against the compressor. This procedure satisfies systems with floating head pressure control. Follow the same procedure for systems with low-ambient flooded condenser head pressure control.
With 105°F condensing temperature, charge until the sight glass just clears. Then accurately weigh in the additional pounds of refrigerant specified in the chart on page 19. There is also a charging tag on the unit. The pounds specified on the tag supercedes this IOM. This will provide adequate charge for all ambient operation. The actual charge should not exceed the calculated systems capacity. After system charging and room pulldown is complete , test the ability of the system to successfully pump down. Raise the room thermostat setting to close the liquid solenoid.
The system must pumpdown and shut off at the low pressure cutout setting. See Table 13.
Unblock the condenser coil and return the room thermostat to the desired setting.
The first two to three hours of operation after start-up is a critical time. Do not just start-up and walk away. Watch for floodback and adjust the expansion valve if necessary. Observe system pressures. Check all fans on the evaporator and condensing unit to be sure they are operational and turning the proper direction. Record the pounds of refrigerant charged into the system. Check the compressor oil level frequently. On low temperature systems the fan delay control may cycle the evaporator fans. To keep the fans on until the room pulls down, it may be necessary to jumper the fan delay control.
Check voltage and amperage at the compressor. Voltage must be within 10% of the specplate rating. Amperage should be approximately equal across all three lines. Check the piping for vibration and add supports if needed. Check electrical conduit for vibration and route to prevent contact with tubing.
Use the Start-Up Check List on page 24 to assist you. Don’t forget to remove the fan delay jumper if one was used. Also, fully open the suction valve. After the room has pulled down to design temperature and held for 24 hours, review the system guidelines on page 23 and complete a system service record on page 25.
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