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507827-01

Issue 1813

Page 4 of 4

Two-Stage Heating and Single-Stage Cooling with 

Two-Stage Thermostat

1.  Mount DPST relay(s) (supplied with kit) next to the 

blower control board of Furnace 1. Use kit supplied 

self-tapping screws to mount DPST relay(s) to the 

control bracket.

2.  Connect the thermostat with Furnace 1, Furnace 2, 

and the DPST relays as shown in Figure 4 through 

Figure 6. Use the female quick connect terminals 

supplied in kit and the proper length of 18 gauge wire 

(field supplied) to complete wiring.

3.  After wiring is complete, cycle both high and low 

heating modes and cooling modes to verify both are 

working properly.

FURNACE 

1F

URNACE 

2

THERMOST

AT

TWO STAGE HEAT ONLY

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

Figure 4. 

FURNACE 

1F

URNACE 

2

THERMOST

AT

TWO STAGE COOL ONLY

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

Figure 5. 

FURNACE 

1F

URNACE 

2

ISO RELAY

THERMOST

AT

FAN TWIN ONLY

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

W1

R

C

Y1

Y2

G

W2

Note

: Furnace transformers must be in phase while twinning.

Figure 6. 

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