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ELECTROMECHANICAL THERMOSTAT WITH ECONOMIZER
Operation Sequence:
1- Economizer outdoor air dampers drive full closed anytime blower B3 is not operating (switched by K3-2 in the unit).
2- Damper motor terminal TR is powered by unit contactor K3 when there is a blower demand or a heating demand. When 24VAC is applied between
terminals TR and TR1, the damper motor is energized and the outdoor air dampers open to minimum position.
3- Blower B3 is energized (indirectly) by thermostat terminal G. On a cooling demand, thermostat terminal G energizes contactor K3 which in turn enerĆ
gizes the blower (refer to operation sequence on previous page for exact sequence). When K3 energizes, K3-1 closes to energize the blower and K3-2
closes to energize the economizer (see step 2) and open the outdoor air dampers to minimum position.
Enthalpy Low, 1st Stage Cool:
4- Initial cooling demand Y1 is sent to enthalpy control A6 and terminal 1.
5- Enthalpy control A6 has determined that outside air can be used for cooling and has switched internal relays 1K and 2K.
6- Cooling demand is routed through enthalpy control to energize internal relay 1S. Internal contacts 1S1 close to complete a circuit through damper motor
terminals T and T1.
7- When 24 volts is applied across terminals T and T1 of damper motor, the damper motor energizes and outdoor air dampers open. Supply air sensor R1
varies the voltage across T and T1 and the outdoor air dampers open and adjust accordingly. 1st stage cooling is provided by outdoor air.
Enthalpy Low, 2nd Stage Cool:
8- Economizer outdoor air dampers remain open.
9- Additional cooling demand is routed from thermostat Y2 through enthalpy control terminals 3 and 5 to energize the 1st stage compressors. The 1st
stage compressors provide all additional cooling.
Enthalpy High, 1st Stage Cool:
10-Enthalpy control internal relays 1K and 2K switch. Internal relay 1S is de-energized and 1S1 opens. Outdoor air dampers close to minimum position.
11-Cooling demand is sent from thermostat terminal Y1 through enthalpy control terminals 1 and 2 and through enthalpy control terminal 5 to energize the
1st stage compressors.
Enthalpy High, 2nd Stage Cool:
12-Additional cooling demand is sent from thermostat terminal Y2 through enthalpy control terminals 3 and 4 to energize the 2nd stage compressor.
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