Component Operation and Maintenance
7.4.2Discharge 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
Table 7 Discharge pressures
|
| Discharge Pressure |
System Design | PSIG (kPa) | |
|
| |
Air Cooled | 260 (1795) | |
Water/Glycol Cooled | 210 (1450) | |
| 85°F (29°C) fluid | 225 (1550) |
| 115°F (46°C) fluid | 295 (2035) |
Maximum | 330 (2275) | |
High Pressure | 360 (2482) | |
7.4.3Superheat
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.
7.4.4Thermostatic 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).
Adjustment
To adjust the superheat setting:
1.Remove the valve cap at the bottom of the valve.
2.Turn the adjusting stem counterclockwise to lower the superheat.
3.Turn the adjusting stem clockwise to increase the superheat.
NOTE
Make no more than one turn of the stem at a time. As long as 30 minutes may be required for the new balance to take place.
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