IM 861
15
WIRE SIZE, AWG
Thermostat
The room thermostat must be compatible with the spark
ignition control on the unit. Generally, all thermostats that are
not of the “current robbing” type are compatible with the
integrated furnace control. The low voltage wiring should be
sized as shown in Table 6.
Install the room thermostat in accordance with the instruction
sheet packed in the box with the thermostat.
Furnace Section Controls and
Ignition System
Normal Furnace Operating Sequence
Single Stage Gas Valve
This unit is equipped with an integrated direct spark ignition
control.
1
The thermostat calls for heat.
2
The control board will run a self check to verify that the limit
control and manual reset overtemperature control are closed
and that the pressure switch is open.
3
Upon closure of the pressure switch, the control board
energizes the induced draft blower for a 15 second prepurge.
4
After the 15 second prepurge, the gas valve opens and the
spark is initiated for 7 second trial for ignition.
5
Burners ignite and flame sensor proves all burners have lit.
6
The circulating air blower is energized after 30 seconds.
7
The control board enters a normal operation loop in which all
safety controls are monitored continuously.
Figure 17: Through Base Electrical Connection
Figure 18: Typical Thermostat Wiring
14
1/2
ⴖ
7/8
ⴖ
12
1/2
ⴖ
7/8
ⴖ
10
1/2
ⴖ
7/8
ⴖ
8
3/4
ⴖ
1-31/32
ⴖ
6
1
ⴖ
1-23/64
ⴖ
4
1
ⴖ
1-23/64
ⴖ
3
1-1/4
ⴖ
1-23/32
ⴖ
2
1-1/4
ⴖ
1-23/32
ⴖ
1
1-1/2
ⴖ
1-31/32
ⴖ
0
1-1/2
ⴖ
1-31/32
ⴖ
00
2
ⴖ
2-15/32
ⴖ
000
2
ⴖ
2-15/32
ⴖ
CONDUIT SIZE
HOLE SIZE
I658
NOTES:
1. DETERMINE REQUIRED WIRE SIZE FROM MINIMUM CIRCUIT AMPACITY SHOWN IN INSTALLATION & OPERATING INSTRUCTION.
2. BOTTOM POWER ENTRY WILL NOT ACCOMMODATE WIRE LARGER THAN #2 AWG (SHADED AREA).
Table 6
FIELD WIRE SIZE FOR 24 VOLT THERMOSTAT CIRCUITS
SOLID COPPER WIRE - AWG.
3.0
16
14
12
10
10
10
2.5
16
14
12
12
12
10
2.0
18
16
14
12
12
10
50
100
150
200
250
300
Length of Run – Feet (1)
Thermostat Load -
Amps
(1) The total wire length is the distance from the furnace to the
thermostat and back to the furnace.
NOTE: DO NOT USE CONTROL WIRING SMALLER THAN NO. 18
AWG.
