
27
24 Volt Thermostat Wiring
W
IRE
ROUTING
MUST
NOT
INTERFERE
WITH
CIRCULATOR
BLOWER
OPERATION
,
FILTER
REMOVAL
OR
ROUTINE
MAINTENANCE
.
IMPORTANT NOTE
Low voltage connections can be made through either the right
or left side panel. Thermostat wiring entrance holes are located
in the blower compartment. The following figure shows con
-
nections for a “heat/cool system”.
This furnace is equipped with a 40 VA transformer to facilitate
use with most cooling equipment. Consult the wiring diagram,
located on the blower compartment door, for further details
of 115 Volt and 24 Volt wiring.
R
Y
C
Furnace
Integrated
Control
Module
Remote Condensing Unit
(Single-Stage Cooling)
R
Thermostat - Single -Stage Heating with Single-Stage Cooling
NOTE:
To apply a single-stage Heating Thermostat, the thermostat
selector switch on the Integrated Control Module
must
be set on
single-stage.
Figure 30
R
Y
C
Furnace
Integrated
Control
Module
Remote Condensing Unit
(Single-Stage Cooling)
R
Thermostat - Two-Stage Heating with Single-Stage Cooling
Figure 31
W1
W2
Y
Furnace
Integrated
Control
Module
Remote Condensing Unit
(Two-Stage Cooling)
Y2
W1
W2
Y2
Thermostat - Two-Stage Heating with Two-Stage Cooling
Thermostat Wiring Diagrams
Figure 32
Single-Stage Heating Thermostat Application
A single-stage thermostat with only one heating stage
may be used to control this furnace. The application of a
single-stage thermostat offers a
timed
transition from low
to high fire. The furnace will run on low stage for a fixed
period of time before stepping up to high stage to satisfy
the thermostat’s call for heat. The delay period prior to
stepping up can be set at either a fixed 10 or 20 minute
time delay or a load based variable time between 1 and 12
minutes (AUTO mode). If the AUTO mode is selected, the
control averages the cycle times of the previous three cycles
and uses the average to determine the time to transition
from low stage to high stage.
PCBBF139 CONTROL BOARD
1
2
3
4
2 STAGE STAT
OFF OFF
1 STG STAT 10 min delay ON
OFF
1 STG STAT 20 min delay ON
ON
AUTO
OFF* ON*
90
OFF OFF
120
OFF ON
150
ON* OFF*
180
ON
ON
* Factory Setting
DIP SWITCH
SWITCH
GROUP
FUNCTION
S3
S3
Heating
Fan Off
Delay
PURPOSE
Thermostat
Setup
Fossil Fuel Applications
This furnace can be used in conjunction with a heat pump in
a fossil fuel application. A fossil fuel application refers to a
combined gas furnace and heat pump installation which uses an
outdoor temperature sensor to determine the most cost efficient
means of heating (heat pump or gas furnace).
A heat pump thermostat with
three stages of heat
is required
to properly use a two-stage furnace in conjunction with a
heat pump. Refer to the fossil fuel kit installation instruc-
tions for additional thermostat requirements.
Strictly follow the wiring guidelines in the fossil fuel kit
installation instructions. All furnace connections must be
made to the furnace two-stage integrated control module
and the “FURNACE” terminal strip on the fossil fuel control
board.
Twinning
Using the “TWIN” terminals and proper wiring enables two
*MEC96 furnaces of the same model and size to be twinned.
Twinning allows simultaneous operation of two furnaces
and forces the indoor blower motors of each furnace to
operate synchronously into a common duct system. Using
the twinning function will require only field installed wiring
with no external kits or parts.
·
The staging DIP switches and speed tap DIP switches
must be set the same on both furnaces.