20
Figure 16
R
Y
C
Furnace
Integrated
Control
Module
Remote Condensing Unit
(Single-Stage Cooling)
R
Thermostat - Two-Stage Heating with Single-Stage Cooling
Figure 17
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 18
S
INGLE
-S
TAGE
H
EATING
T
HERMOSTAT
A
PPLICATION
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 fi re. The
furnace will run on low stage for a fi xed 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 fi xed 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
F
OSSIL
F
UEL
A
PPLICATIONS
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 effi cient 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 instructions for
additional thermostat requirements.
Strictly follow the wiring guidelines in the fossil fuel kit instal-
lation 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.
T
WINNING
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 fi eld 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.
NOTE:
Each furnace must be connected to it’s
own 115 VAC power supply. The L1 connection to
each furnace must be in phase (connected to circuit
breakers on the same 115 VAC service panel phase
leg). To verify that the furnaces are in phase, check
from L1 to L1 on each furnace with a voltmeter. If
the furnaces are in phase, the voltage between both
furnaces will be ZERO.
Room
Thermostat
Y2
Y
W
W2
R
G
C
Ylo
Y
W
W2
R
G
C
Ylo
Y
W
W2
R
G
C
Furnace 1
Furnace 2
115 V
OLT
L
INE
C
ONNECTION
OF
A
CCESSORIES
(H
UMIDIFIER
AND
E
LECTRONIC
A
IR
C
LEANER
)
The furnace integrated control module is equipped with line voltage
accessory terminals for controlling power to an optional fi eld-sup-
plied humidifi er and/or electronic air cleaner.
The accessory load specifi cations are noted in the chart below:
Humidifier
1.0 Amp maximum at 120 VAC
Electronic Air Cleaner
1.0 Amp maximum at 120 VAC
Turn OFF power to the furnace before installing any accessories.
Follow the humidifi er or air cleaner manufacturers’ instructions for
locating, mounting, grounding, and controlling these accessories.
Accessory wiring connections are to be made through the 1/4”
quick connect terminals provided on the furnace integrated control
module. The humidifi er and electronic air cleaner hot terminals
are identifi ed as HUM and EAC. The humidifi er and electronic
