Twinning The Ml193Uh - Lennox ML193UH Installation Instructions Manual

Twinning the ML193UH

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.
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.
TWO-STAGE THERMOSTAT
Call For Cool
Call For Fan
Call For 1st
Stage Heat
Call For 2nd
StageHeat
ISOLATION
RELAY
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
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 62 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-
lation relay connects from the thermostat "W" to 24 VAC
common. The contacts of the relay connect "R" to "W" on
the non-thermostat twin.
SINGLE STAGE THERMOSTAT
Call For Cool
Call For Fan
Call For Heat
FIGURE 62
Page 45
TWIN
R
R
TWIN 1
Y
Y
G
G
W
W
C
TWIN
ISOLATION
RELAY
R
TWIN 2
Y
G
W
C