Bosch DX Series Installation And Maintenance Manual

14 Unitary Air Handler DX and Hydronic SeriesSubject to change without prior notice Revised 11-116720220327In addition to providing a connecting point forthermostat wiring, the interface board also translatesthermostat inputs into control commands for thevariable speed programmable ECM DC fan motor anddisplays an LED indication of operating status. Thethermostat connections and their functions are asfollows:Y2 Second Stage Compressor OperationY1 First Stage Compressor OperationG Fan OperationO Reversing Valve (energized in cooling)W1 Auxiliary Electric Heat (runs in conjunctionwith compressor)EM/W2 Emergency Heat (electric heat only)NC Transformer 24 VAC Common (extraconnection)C Transformer 24 VAC Common (primaryconnection)R Transformer 24 VAC HotHUM Dehumidification ModeIf the unit is being connected to a thermostat with amalfunction light, this connection is made at theunit’s malfunction output or relay.CautionIf the thermostat is provided with a malfunctionlight powered off of the common (C) side of thetransformer, the unit must be provided with amalfunction relay (Bosch option # 660-006) toproperly energize the light. The relay coil will bewired across the (ALR) and (C) contacts on theunit’s UPM board and the relay’s normally opencontacts across (ALR) and the malfunction lightconnection on the thermostat. If the thermostat isprovided with a malfunction light powered off ofthe hot (R) side of the transformer, then thethermostat malfunction light connection should beconnected directly to the (ALR) contact on theunit’s UPM board.This only applies when the air handler is pairedwith a Bosch condensing section. Othercondensing manufactures may have different typeof connections. Contact the manufacturer of thecondensing section for proper connectionmethods when utilizing the malfunction light.6. Loosen the wheel set screw by placing wrench onthe screw head and turning counter clockwise.Loosen the wheel set screw until the shaft canspin freely 360° while inside the wheel hub. Thewheel set screw is located on the wheel hub onthe opposite side of the motor.7. Remove the blower motor from the blower housingby removing the screws on the sides of the housingthat secure the blower to the housing.8. Remove the blower motor mount assembly byloosening the belly band bolt and nut, then,remove the belly bans and mount legs.9. Insert the new blower motor into the blowermounting bracket making sure the mountinglegs are properly placed into the belly band andthe legs are straight. Tighten the belly bandscrew and nut until belly band is securelyfastened to the motor.10. Place the motor into the housing so the mountleg holes line up with the rivet nuts in thehousing. Place the screw into the mount legholes and tighten until the mount legs aresecurely fastened to the housing.11. Center the blower wheel in the housing, turnthe motor shaft so the wheel set screw islocated on the center of the flat spot of theshaft and tighten the set screw.12. Connect the same two cables that wereremoved in step 3.13. Slide the blower assembly into the blower deck,replace the angle bracket, insert the screwsthrough the holes in the angle bracket andtighten the screws into the holes in the blowerdeck and the flanges in the casing.14. Switch the circuit breakers to “ON” and replaceair handler blower door.15. Turn on all electrical supply circuits to the furnaceat the main service (House Circuit Breaker) panel.16. Set the thermostat to the desired temperature.ECM INtERfACE bOARD ANDtHERMOStAt CONNECtIONSThe ECM Interface Board is used to connect thethermostat wiring and the control wiring from theremote condensing section or water-to-water unit.ECM Interface board