Liebert CHALLENGER 3000 - Manual (Page 54)

Component Operation and Maintenance
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6.4 Refrigeration System
Each month, the components of the refrigeration system should be inspected for proper function and
signs of wear. Since, in most cases, evidence of malfunction is present prior to component failure, peri-
odic inspections can be a major factor in the prevention of most system failures.
Refrigerant lines must be properly supported and not allowed to vibrate against ceilings, floors or the
unit frame. Inspect all refrigerant lines every six months for signs of wear and proper support. Also
inspect capillary and equalizer lines from the expansion valve and support as necessary.
Each liquid line has a sight glass that indicates liquid refrigerant flow and the presence of moisture.
Bubbles in the sight glass indicate a shortage of refrigerant or a restriction in the liquid line. The
moisture indicator changes from green to yellow when moisture is present in the system.
6.4.1 Suction Pressure
Suction pressure will vary with load conditions. The low pressure switch will shut the compressor
down if suction pressure falls below the cut-out setting. High suction pressure reduces the ability of
the refrigerant to cool compressor components and can result in compressor damage. Minimum (pres-
sure switch cut-out setting) and maximum (design operating) suction pressures are in Table 18.
6.4.2 Discharge Pressure
Discharge Pressure can be increased or decreased by load conditions or condenser efficiency. The high
pressure switch will shut the compressor down at its cut-out setting. Refer to Table 19, below.
6.4.3 Superheat
Superheat can be adjusted by the Thermostatic Expansion Value (TEV). To determine superheat:
1. Measure the temperature of the suction line at the point the TEV bulb is clamped.
2. Obtain the gauge pressure at the compressor suction valve.
3. Add the estimated pressure drop between bulb location and suction valve.
4. Convert the sum of the two pressures to the equivalent temperature.
5. Subtract this temperature from the actual suction line temperature. The difference is superheat.
Table 18 Suction pressures
System
Minimum
PSIG (kPa)
R–22
Maximum
PSIG (kPa)
R–22
Air w/FSC
(Fan Speed Control)
15 (103) 90 (620)
Air w/Lee-Temp Control
(Floodback head
pressure control)
20 (137) 90 (620)
Water Cooled 20 (137) 90 (620)
Glycol Cooled 20 (137) 90 (620)
Table 19 Discharge pressures
System Design
Discharge Pressure
PSIG (kPa)
Air Cooled 260 (1795)
Water/Glycol Cooled 65-75 ° F (18-24 ° C) fluid 210 (1450)
85 ° F (29 ° C) fluid 225 (1550)
115°F (46°C) fluid 295 (2035)
Maximum 330 (2275)
High Pressure Cut-Out 360 (2482)