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18 18-CD21D1-5
Installer’s Guide
TWINNING
These furnaces may be twinned. Twinning requires that
two furnaces with the same configuration, capacity, and
airflow must be used. They shall have common returns
with equal pressure drops or ducts with equivalent
lengths and sizes. See Field Wiring Diagrams below for
proper hookup.
TWIN
TWIN
R1
R1
TWINNING CONNECTION DIAGRAM
FOR TWINNING 1 STAGE FURNACES WITH
SINGLE WIRE TWINNING FEATURE
1 STAGE HEATING ONLY THERMOSTAT
1 STAGE HEAT
ONLY
THERMOSTAT
(WITH FAN SWITCH) FURNACE NO. 1
FURNACE NO. 2
BLOWER OPERATION OF
UNIT NO. 2 IS SYNCRONIZED
WITH UNIT NO. 1 VIA SIGNALS
FROM TWIN CONNECTION.
SEE NOTE 4
SEE NOTE 3
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 4
ISOLATION RELAY
SEE NOTE 4
B/C
B/C
B/C
From Dwg. 21B341422 Rev. 3
TWIN
TWIN
R1
R1
TWINNING CONNECTION DIAGRAM
FOR TWINNING 1 STAGE FURNACES WITH
SINGLE WIRE TWINNING FEATURE
1 STAGE HEAT / 1 STAGE COOL THERMOSTAT
1 STAGE
HEATING / COOLING
THERMOSTAT FURNACE NO. 1
FURNACE NO. 2
BLOWER OPERATION OF
UNIT NO. 2 IS SYNCRONIZED
WITH UNIT NO. 1 VIA SIGNALS
FROM TWIN CONNECTION.
SEE NOTE 4
SEE NOTE 5
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 4
ISOLATION RELAY
SEE NOTE 4
OUTDOOR UNIT
(NO TRANSFORMER)
OUTDOOR UNIT
(WITH TRANSFORMER)
RC
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 3
B/C
B/C
B/C
From Dwg. 21B341423 Rev. 2