Ecm Interface Board; Thermostat Connections - Bosch SM024 Installation, Operation And Maintenance Manual

10 | Electrical
THERMOSTAT
R
G
Y1
Y2
C
O
B
E
W2
Figure # 13
Packaged heat pumps are equipped with
detachable Thermostat connectors. These
connectors are located in different locations
based on the blower motor that is installed in the
unit.
For the EON motor, the three detachable
thermostat connectors are located on the ECM
Interface board. See Wiring Harness Drawing.
Harness wiring can be loose, based on the
options installed for the unit. See the Wiring
Harness Drawing notes for further details.
Connection point logic is as follows:
Figure 14: Low Voltage Connection Points
From
Function
Thermostat
24 HVAC C
Common
24 VAC Hot R
Fan Operation G
Reversing O
Valve (3)
1st Stage Y1
Compressor
Operation
2nd Stage Y2
Compressor
Operation
8733920846 (2015/01)
PACKAGED
HEAT PUMP
R
G
Y1
Y2
C
O
B
W1
W2
To
To Air From Air
Condensing
Handler Handler
Section
C C C
R R R
G
O O O
Y1 Y1 Y1
Y2 Y2 Y2
Subject to change without prior notice
Condensate
Sensor (1)
Alarm Output L
(From UPM)
(2)
Auxilliary W/W1/W2
Electric Heat
(4)
E
Emergency
Heat (4)
1. For the condensate overflow sensor, connect 'CS' at the
condensing section to 'CS' at the air handler. Be sure to ground
power supply.
2. If service LED is utilized connect 'ALR' terminal on the UPM board
to 'L' on the thermostat sub base. The wiring may be spliced in the
air handling unit. The ALR output is always dry contact between
the OUT and COM Terminals. See Thermostat connections section
of this manual for additional information.
3. 'O' – reversing valve is energized in the cooling mode. Fail safe is
to heating.
4. Utilized when electric strip heater package present.

ECM Interface Board

Figure # 15

THERMOSTAT CONNECTIONS

Thermostat wiring is connected to the 10 pin
screw type terminal block on the lower center
portion of the ECM Interface Board. 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.
SM AH Series Heat Pump
CS CS
Splice ALR
W1
EM/W2
SM AH Series Heat Pump