Bosch DX025 - ECM Interface Board; ECM Interface Board and Thermostat Connections

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
Subject to change without prior notice Revised 11-11
6720220327
In addition to providing a connecting point for
thermostat wiring, the interface board also translates
thermostat inputs into control commands for the
variable speed programmable ECM DC fan motor and
displays an LED indication of operating status. The
thermostat connections and their functions are as
follows:
 Second Stage Compressor Operation
 First Stage Compressor Operation
 Fan Operation
 Reversing Valve (energized in cooling)
 Auxiliary Electric Heat (runs in conjunction
with compressor)
 Emergency Heat (electric heat only)
 Transformer 24 VAC Common (extra
connection)
 Transformer 24 VAC Common (primary
connection)
 Transformer 24 VAC Hot
 Dehumidication Mode
If the unit is being connected to a thermostat with a
malfunction light, this connection is made at the
unit’s malfunction output or relay.
Caution
 Ifthethermostatisprovidedwithamalfunction
lightpoweredoffofthecommon(C)sideofthe
transformer,theunitmustbeprovidedwitha
malfunctionrelay(Boschoption#660-006)to
properlyenergizethelight.Therelaycoilwillbe
wiredacrossthe(ALR)and(C)contactsonthe
unit’sUPMboardandtherelay’snormallyopen
contactsacross(ALR)andthemalfunctionlight
connectiononthethermostat.Ifthethermostatis
providedwithamalfunctionlightpoweredoffof
thehot(R)sideofthetransformer,thenthe
thermostatmalfunctionlightconnectionshouldbe
connecteddirectlytothe(ALR)contactonthe
unit’sUPMboard.
Thisonlyapplieswhentheairhandlerispaired
withaBoschcondensingsection.Other
condensingmanufacturesmayhavedifferenttype
ofconnections.Contactthemanufacturerofthe
condensingsectionforproperconnection
methodswhenutilizingthemalfunctionlight.
6. Loosen the wheel set screw by placing wrench on
the screw head and turning counter clockwise.
Loosen the wheel set screw until the shaft can
spin freely 360° while inside the wheel hub. The
wheel set screw is located on the wheel hub on
the opposite side of the motor.
7. Remove the blower motor from the blower housing
by removing the screws on the sides of the housing
that secure the blower to the housing.
8. Remove the blower motor mount assembly by
loosening the belly band bolt and nut, then,
remove the belly bans and mount legs.
9. Insert the new blower motor into the blower
mounting bracket making sure the mounting
legs are properly placed into the belly band and
the legs are straight. Tighten the belly band
screw and nut until belly band is securely
fastened to the motor.
10. Place the motor into the housing so the mount
leg holes line up with the rivet nuts in the
housing. Place the screw into the mount leg
holes and tighten until the mount legs are
securely fastened to the housing.
11. Center the blower wheel in the housing, turn
the motor shaft so the wheel set screw is
located on the center of the at spot of the
shaft and tighten the set screw.
12. Connect the same two cables that were
removed in step 3.
13. Slide the blower assembly into the blower deck,
replace the angle bracket, insert the screws
through the holes in the angle bracket and
tighten the screws into the holes in the blower
deck and the anges in the casing.
14. Switch the circuit breakers to “ON” and replace
air handler blower door.
15. Turn on all electrical supply circuits to the furnace
at the main service (House Circuit Breaker) panel.
16. Set the thermostat to the desired temperature.


The ECM Interface Board is used to connect the
thermostat wiring and the control wiring from the
remote condensing section or water-to-water unit.
  