Liebert 3000 6.4.1Suction Pressure, 6.4.2Discharge Pressure, 6.4.3Superheat, Suction pressures

Component Operation and Maintenance

6.4Refrigeration 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.

6.4.1Suction 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.

Table 18 Suction pressures

	Minimum	Maximum
	PSIG (kPa)	PSIG (kPa)
System	R–22	R–22
Air w/FSC	15 (103)	90 (620)
(Fan Speed Control)
Air w/Lee-Temp Control	20 (137)	90 (620)
(Floodback head
pressure control)
Water Cooled	20 (137)	90 (620)
Glycol Cooled	20 (137)	90 (620)

6.4.2Discharge 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.

Table 19 Discharge pressures

		Discharge Pressure
System Design		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)

6.4.3Superheat

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.

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