CyberChiller Series Installation, Operation & Maintenance Manual

CAUTION

POE oil is used in systems with R-407C refrigerant. POE oil quickly absorbs moisture when exposed to air. High POE oil moisture levels react with refrigerant to form acid, which results in system contamination. Keep entire system sealed as much as possible and minimize exposure of POE oil to outside air. Familiarize yourself with the charging procedures discussed in section 2.7.3 of this manual. Instead of adding R-22 vapor to the suction port as described under “Preparing System For Charging”, the initial charge will be performed by introducing R-407C liquid to the discharge side of the compressor.

PREPARING SYSTEM FOR CHARGING

1.With all the system piping connections made, perform a dry nitrogen leak detection test on the system. Using dry nitrogen only, pressurize the system to 150 psig. Since there is no refrigerant in the system to detect, leaks may be detected by observing the standing pressure.

2.After ensuring there are no leaks, evacuate the system to 50 microns and hold the vacuum for 2 hours.

3.Break the vacuum by supplying R-407C liquid to the discharge port near the compressor until the pressure is raised to about 50 psig. This small holding charge allows the low pressure switch to “make” through the process of fine tuning the system charge.

FINE TUNING THE SYSTEM CHARGE

4.Disconnect the refrigerant cylinder from the discharge side of the compressor and connect it to the suction side.

5.Start the system and use the microprocessor controller to lower the supply water temperature setpoint 3-5°F below actual water temperature, ensuring cooling remains on as the unit is charged.

6.Allow the discharge pressure to rise to 225-280 psig and hold it constant. On cool days it may be necessary to restrict the airflow across the

condenser (or reduce the water glycol flow), to raise the pressure.

7.Slowly meter R-407C liquid refrigerant through the suction side while watching the sight glass to clear of bubbles.

CAUTION

Add liquid refrigerant slowly to prevent the refrigerant oil from “washing out” of the compressor.

8.While monitoring the sight glass, take a sub- cooling temperature reading on the output side of the condenser. The sub-cooling temperature should be 10-12°F.

9.If necessary, add liquid refrigerant to maintain adequate sub-cooling temperature.

10.Take a superheat reading on the suction line 6" from the compressor. The superheat should be 12- 20°F.

2.7.5High/Low Pressure Limit Switch

CyberChiller units utilizing thermal expansion valves are equipped with hermetically sealed high-pressure and low-pressure switches. These switches are preset by the manufacturer and cannot be adjusted. The high pressure switch will open the control circuit to disengage power to the compressor contactor if the discharge pressure rises above a specific pressure. The high pressure switch also triggers an alarm signal at the controller. To restore operation of a compressor after shut down due to high or low pressure, re-set the alarm at the remote panel. If a compressor was disabled due to high pressure conditions, a manual reset of the high pressure safety switch is also required. The high-pressure switch opens at 410 psig and has a manual reset.

The Low pressure switch will open the control circuit to the microprocessor digital input to disengage power to the compressor contactor if suction pressure drops below a specific pressure. The microprocessor will ignore the absence of this signal during the cold start delay period after starting of a compressor. Should this signal continue to be absent or open after the cold start period, the affected compressor will be shut down with an alarm indication at the controller. The low-pressure switch opens at 10 psig (± 4) and closes at 32 psig (± 5) and has an automatic reset.

(©October, 2006)

2-12