Service Manual

27
SYSTEM OPERATION
R
Y C
Fur nace
Int egrat ed
Cont rol
Module
Remote Condensing Unit
(Single-St age Cool ing)
R
Thermostat - Two-Stage Heating with Single-Stage Cooling
W1 W2
Y
Fur nace
Int egrat ed
Cont rol
Module
Remot e Condensing Unit
(Tw o-St age Cool i ng)
Y2
W1 W2
Y2
Thermostat - Two-Stage Heating with Two-Stage Cooling
Thermostat Wiring Diagrams
SINGLE-STAGE 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
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 step-
ping up can be set at either a fixed 10 or 20 minute time
delay or a load based variable time between 1 and 12 min-
utes (AUTO mode). If the AUTO mode is selected, the con-
trol 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.
DIP Switch
Group
DIP Switch
Numbe
r
Purpose
Auto 1 OFF* 2 ON*
10 Minutes 1 ON 2 OFF
20 Minutes 1 ON 2 ON
2 Stage 1 OFF 2 OFF
90 Seconds 3 OFF 4 OFF
120 Seconds 3 OFF 4 ON
150 Seconds 3 ON* 4 OFF*
180 Seconds 3 ON* 4 ON
* = Factory Position
Staging and Blow e r Off De lay DIP Sw itche s PCBBF137
Function
S1
1, 2
Heat Staging /
Delay
3, 4
Blower Heat Off
Delay
1234
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
Staging and Blower Off Delay Dip Switches PCBBF139
Heating Fan Off
Delay
S3
Dip Switch
Purpose Switch Group Function
Thermostat
setup
S3
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 twin-
ning 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.
NOTE: Each furnace must be connected to its own 115 VAC
power supply. The L1 connection toeach 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
CIRCULATOR BLOWER SPEED ADJUSTMENT
WARNING
HIGH VOLTAGE
DISCONNECT ALL POWER BEFOR CHANGING SPEED TAPS.
M
ULTIPLE POWER SOURCES MAY BE PRESENT.
F
AILURE TO DO
SO MAY CAUSE PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
This furnace is equipped with a multi-speed ECM motor.
Two wiring harnesses connect the motor to the integrated
control board and furnace power supply. The line voltage
(115 VAC) power supply to the motor is constant and not
switched by the control board. Motor operation is also de-
pendent on a 24 VDC signal on one of the four speed taps
on the motor. The airflow tables for heating and cooling
speeds show the relationship between airflow (CFM) and
external static pressure for each size furnace.