OPERATING SEQUENCES
Base Unit Controls
Cooling, Units Without Economizer
When thermostat calls for Stage 1 cooling, terminals G and Y1 are energized. The
If Stage 1 cooling does not satisfy the space load , the space temperature will rise until thermostat calls for Stage 2 cooling (Y2 closes). Compressor 2 contactor (C2) is energized; Compressor 2 starts and runs.
Heating, Units Without Economizer
When the thermostat calls for heating, terminal W1 is energized. To prevent thermostat
If Stage 1 heating does not satisfy the space load, the space temperature will fall until thermostat calls for Stage 2 heating (W2 closes). Terminal W2 is energized and the
When the space heating load is fully satisfied, thermostat terminal W1 is also deenergized. All heating operations cease. The IFM stops after a
Cooling, Unit With EconoMi$er IV
For Occupied mode operation of EconoMi$er IV, there must be a
During Occupied mode operation, indoor fan operation will be accompanied by economizer dampers moving to Minimum Position setpoint for ventilation. If indoor fan is off, dampers will close. During Unoccupied mode operation, dampers will remain closed unless a Cooling (by free cooling) or DCV demand is received.
When free cooling using outside air is not available, the unit cooling sequence will be controlled directly by the space thermostat as described above as Cooling, Unit Without Economizer. Outside air damper position will be closed or Minimum Position as determined by occupancy mode and fan signal.
When free cooling is available as determined by the appropriate changeover command (dry bulb, outdoor enthalpy, differential dry bulb or differential enthalpy), a call for cooling (Y1 closes at the thermostat) will cause the economizer control to modulate the dampers open and closed to maintain the unit supply air temperature at 50 to 55_F. Compressor will not run.
During free cooling operation, a supply air temperature (SAT) above 50_F will cause the dampers to modulate between Minimum Position setpoint and 100% open. With SAT from 50_F to 45_F, the dampers will maintain at the Minimum Position setting. With SAT below 45_F, the outside air dampers will be closed. When SAT rises to 48_F, the dampers will
Should 100% outside air not be capable of satisfying the space temperature, space temperature will rise until Y2 is closed. The economizer control will call for compressor operation. Dampers will modulate to maintain SAT at 50 to 55_F concurrent with Compressor 1 operation. The Low Ambient Lockout Thermostat will block compressor operation with economizer operation below 42_F outside air temperature.
When space temperature demand is satisfied (thermostat Y1 opens), the dampers will return to Minimum Damper position if indoor fan is running or fully closed if fan is off.
If accessory power exhaust is installed, the power exhaust fan motors will be energized by the economizer control as the dampers open above the
Damper movement from full closed to full open (or vice versa) will take between
Heating With EconoMi$er IV
During Occupied mode operation, indoor fan operation will be accompanied by economizer dampers moving to Minimum Position setpoint for ventilation. If indoor fan is off, dampers will close. During Unoccupied mode operation, dampers will remain closed unless a DCV demand is received.
When the room temperature calls for heat (W1 closes), the heating controls are energized as described in Heating, Unit Without Economizer above.
Demand Controlled Ventilation
If a
48TC
75
