Carrier PC211 specifications

Points, (T1/P1;T2/P2). These points have default settings for each type of refrigerant, HCFC-22 or HFC-134a, as defined on the Service1 table, or on Table 4. These settings and the algorithm function are graphically displayed in Figure 20. The two sets of load points on this graph (default settings are shown) describe a line which the algorithm uses to determine the maximum lift of the compressor. Whenever the actual differential pressure between the cooler and condenser, and the temperature difference between the entering and leaving chilled water are above the line on the graph (as defined by the MINIMUM and MAXIMUM Load Points) the algorithm will go into a corrective action mode. If the actual values are below the line, the algorithm takes no action. Modification of the default set points of the MINIMUM and MAXIMUM load points is described in Figure 21.

Corrective action can be taken by making one of 2 choices. If a hot gas bypass line is present, and the hot gas is configured on the Service1 table, then the hot gas bypass valve can be energized. If a hot gas bypass if not present, then the action taken is to hold the guide vanes. See Table 4, Capacity Overrides. Both of these corrective actions will reduce the lift experienced by the compressor and help to prevent a surge condition. Surge is a condition when the lift becomes so high that the gas flow across the impeller reverses. This condition can eventually cause machine damage. The surge prevention algorithm is intended to notify the operator that machine operating conditions are marginal, and to take action to help prevent machine damage such as lowering entering condenser water temperature.