Economizer APPLICATION/OPERATION

Enthalpy Sensor

(Primary Sensor)

Timed Exhaust

Frost Control

The energy recovery wheel may be de-energized for the purpose of providing economizer (free cooling) operation. This can be achieved with a signal from a Temperature or Enthalpy sensor mounted in the supply air inlet compartment (see FIGURE 13). This Primary sensor will de-energize the energy wheel when the outdoor air temperature (factory default is 65°F) or enthalpy (factory default is the ‘D’ setting) is below the field adjustable set point. An additional Override temperature sensor is also furnished in the supply air inlet compartment to deactivate economizer mode (see FIGURE 13). The Override (with field adjustable set point) is set at some temperature lower than the Primary sensor (factory default is 50°F). Effectively, the two sensors create a deadband where the energy recovery wheel will not operate and free cooling from outside can be brought into the building unconditioned.

	Testing (terminals referenced below are in the unit control center — see FIGURE 5, Item #7)
	Temperature sensor with Override
	• Turn both Temperature and Override
	thermostats down as low as they go.	FIGURE 13
	The wheel should be rotating.	FIGURE 13
	The wheel should be rotating.
	• Turn the Temperature sensor up as
	high as it goes, and keep the Override
	sensor as low as it will go. The wheel

should stop rotating.

• Turn both sensors as high as they will go. The wheel should start rotating.

• Set the Temperature sensor to the desired temperature for economizer operation to begin. Set the Override sensor to the desired temperature for economizer operation to end (factory default is 65°F and 50°F, respectively).

Override

Probes

Enthalpy sensor with Override

•A factory-installed 620 ohm resistor is connected across terminals SR and +. The Override sensor should be turned

down below current temperature in unit. Turn the unit on; LED on the sensor should be off. Check continuity across terminals 2 and 3, there should not be continuity. There should be continuity between terminals 1 and 2.

•Disconnect the 620 ohm resistor from terminals SR and +. LED should turn on. There should be continuity between terminals 2 and 3. There should not be continuity between terminals 1 and 2.

•Turn the Override sensor above current temperature in unit. There should be continuity between terminals 3 and 6. Set the Override sensor to the desired temperature for economizer operation to end (factory default is 50°F).

•Reconnect the factory-installed jumper.