Suction Pressure, Discharge Pressure | Emerson VH, DE, VE, DH

Component Operation and Maintenance, Checks and Adjustments

7.4.2Suction 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. On the other hand, high suction pressure reduces the ability of the refrigerant to cool compressor components and can result in compressor damage. Minimum (pressure switch cut-out setting) and maximum (design operating) suction pres- sures are listed in the following table.

Table 15 Suction pressures

	Minimum Pressure	Maximum Pressure
	PSIG (kPa)	PSIG (kPa)
System	R–22	R–22
Air FSC	15 (103)	90 (620)

Floodback head pressure control	20 (137)	90 (620)

Water Cooled	20 (137)	90 (620)

Glycol Cooled	20 (137)	90 (620)

7.4.3Discharge 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 the table below.

Table 16 Discharge pressures

System Design	PSIG (kPa)

Air Cooled	260 (1795)

Water Cooled

65 to 75°F water (18 to 24°C)	210 (1450)

85°F water (29°C)	225 (1550)

Glycol Cooled	295 (2035)

Maximum	330 (2275)

High Pressure Cut-Out	360 (2480)

7.4.4Suction 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.

7.4.5Thermostatic Expansion Valve

Operation

The thermostatic expansion valve performs one function. It keeps the evaporator supplied with enough refrigerant to satisfy load conditions. It does not effect compressor operation.

Proper valve operation can be determined by measuring superheat. If too little refrigerant is being fed to the evaporator, the superheat will be high; if too much refrigerant is being supplied, the superheat will be low. The correct superheat setting is between 10 and 15°F (5.6 and 8.3°C).

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