Emerson VH Manuel D’Utilisation

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.

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.

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.

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).

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)

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)