Twinning - Lennox MERIT Series Installation Instructions Manual

8 - Reconnect the sensor wire and reconnect the 2-pin
plug to the ignitor wiring harness.
9 - Reinstall the burner box assembly using the existing
four screws. Make sure that the burners line up in the
center of the burner ports.
10 - Reinstall the gas valve manifold assembly.
Reconnect the gas supply line to the gas valve.
Reinstall the burner box cover.
11 - Reconnect 2-pin plug to gas valve.
12 - Replace the blower compartment access panel.
13 - Refer to instruction on verifying gas and electrical
connections when re-establishing supplies.
14 - Follow lighting instructions to light and operate
furnace for 5 minutes to ensure that heat exchanger
is clean and dry and that furnace is operating
properly.
15 - Replace heating
Twinning the ML195DF Furnace
The control board in this furnace is equipped with a provi-
sion to "twin" (interconnect) two(2) adjacent furnaces with
a common plenum such that they operate as one (1) large
unit.
TWO-STAGE THERMOSTAT
Call For Cool
Call For Fan
Call For 1st
Stage Heat
Call For 2nd
StageHeat
ISOLATION
RELAY
compartment access
FIELD WIRING FOR TWINNING
TWIN
R
R
TWIN 1
Y
Y
G
G
W1
W
W2
C
TWIN
R
TWIN 2
Y
G
W
C
Each furnace must be wired with a dedicated line voltage
supply. However, both circuits must be connected to the
same buss in the main distribution panel.
When twinned, the circulating blower speeds are synchro-
nized between the furnaces. If either furnace has a need
to run the blower, both furnaces will run the blower on the
same speed. The cooling speed has highest priority, fol-
lowed by heating speed and fan speed.
Field installation of twinning consists of connecting wires
between the "C" and "Twin" terminals of the two controls.
The 24 VAC secondary of the two systems must be in
phase. All thermostat connections are made to one con-
trol only. Figure 57 show wiring for two-stage and single
stage thermostats.
The twinned furnace without thermostat connections is
to have the call for heat supplied by an external 24VAC
isolation relay to prevent its rollout switch from being by-
passed by the other twinned furnace. The coil of the iso-
panel.
lation relay connects from the thermostat "W" to 24 VAC
common. The contacts of the relay connect "R" to "W" on
the non-thermostat
SINGLE STAGE THERMOSTAT
Call For Cool
Call For Fan
Call For Heat
FIGURE 57
Page 45
TWIN
R
R
TWIN 1
Y
Y
G
G
W
W
C
TWIN
ISOLATION
RELAY
R
TWIN 2
Y
G
W
C