User manual

Piping
91 Liebert
®
DS
™
9.3 Dehydration/Leak Test and Charging Procedures for R-407C
9.3.1 Air-Cooled Condenser with Variable Fan Speed Head Pressure Control Systems
The Variable Fan Speed Control systems (FSC & VFD) use pressure activated electronic fan speed
control systems and remotely located thermostat(s) to ensure operation at ambient temperatures as
low as 0°F (-18°C). For this ambient temperature range, the VFD Control Condenser must be used
with digital scroll indoor units and can be used for energy savings with any Liebert DS indoor unit.
Variable Fan Speed Control Piping
Two discharge lines and two liquid lines must be field-installed between the indoor unit and the
outdoor condenser. See Figures 68 and 70 for details.
Variable Fan Speed Control Materials Supplied
•Built-in, pre-wired condenser control box
• Air-Cooled condenser
• Piping access cover to be reinstalled when piping is complete
• Bolts—four per leg (3/8" x 5/8")
• Terminal block for two-wire, 24V interlock connection between unit and condenser
• Condenser legs—four with 1-fan, 2-fan and 3-fan models; six with 4-fan models
Variable Fan Speed Control Leak Check and Evacuation Procedure
Proper leak check and evacuation can be accomplished only with all system solenoid valves open and
check valves accounted for.
1. If unit power is available, open the unit liquid line solenoid valves using the evacuation function
for System #1 and System #2 in the diagnostic section of the Liebert iCOM control (refer to the
Liebert iCOM user manual, SL-18835). If unit power is not available, a field-supplied 24VAC /
75VA power source must be directly connected to each of the unit solenoid valves.
2. Connect refrigerant gauges to the suction rotalock valves and discharge line Schrader valves (see
Note above) on both compressors.
3. Starting with Circuit #1, open the service valves and place a 150 PSIG (1034 kPa) of dry nitrogen
with a tracer of refrigerant. Check system for leaks with a suitable leak detector.
4. With pressure still in Circuit #1, open the compressor service valves in Circuit #2. If pressure
increases in Circuit #2, the system is cross-circuited and must be rechecked for proper piping. If
there is no pressure increase, repeat the leak check procedure for Circuit #2.
5. After completion of leak testing, release the test pressure (per local code) and pull an initial deep
vacuum on the system with a suitable pump.
6. After four hours, check the pressure readings and, if they have not changed, break vacuum with
dry nitrogen. Pull a second and third vacuum to 250 microns or less. Recheck the pressure after
two hours. After completing this step, proceed to Variable Fan Speed Charging.
NOTE
Systems with scroll, digital scroll and four-step semi-hermetic compressors include a
factory-installed check valve and an additional downstream Schrader valve with core in the
compressor discharge line. Proper evacuation of the condenser side of the compressor can be
accomplished only using the downstream Schrader valve. See piping schematic (Figure 69).