Thermostat Connections - Bosch LM024 Installation, Operation And Maintenance Manual

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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
on Pg#24.
Figure 10: Low Voltage Connection Points
Function
24 VAC Common
24 VAC Power
Fan Operation
Reversing Valve (3)
Compressor 1st Stage
Compressor 2nd Stage
Condensate Sensor (1)
Alarm Output (From UPM)
Auxiliary Electric Heat (4)
Emergency Heat (4)
Table Notes:
1)If the condensate overflow sensor option is
utilized 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 hot (R) so check
thermostat instruction manual to ensure
compatibility.
3)'O' – reversing valve is energized in the cooling
mode. Fail safe is to heating.
4)Utilized when electric strip heater package
present.

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.
8 733 920 847 (2014/01)
From To Air
Thermostat Handler
C C
R R
G G
O O
Y1 Y1
Y2 Y2
- -
L /ALR Splice
W/W1/W2 W1
W2/E W2
Subject to change without prior notice
Harness wiring can be loose, based on the
options installed for the unit. See the Wiring
Harness Drawing notes for further details.
From Air
To Condensing Section
Handler
C
R
-
O
Y1
Y2
CS
-
-
The thermostat connections and their functions
are as follows:
Y2 Second Stage Compressor Operation
Y1 First Stage Compressor Operation
G Fan
O Reversing Valve (energized in cooling)
Auxiliary Electric Heat
W1
(runs in conjunction with compressor)
EM/W2 Emergency Heat (electric heat only)
Transformer 24 VAC Common
NC
(extra connection)
Transformer 24 VAC Common
C1
(primary connection)
R Transformer 24 VAC Hot
HUM Dehumidification Mode
LM Series Heat Pump AH
C
R
-
O
Y1
Y2
CS
ALR (UPM)
-
-
LM Series Heat Pump AH