035-17438-001 Rev. A (901)
18
Unitary Products Group
ACCESSORY CONNECTIONS
The furnace control will allow power switching control of vari-
ous accessories. Refer to Figure 14 for connection details.
Electronic Air Cleaner Connection
Two 1/4” spade terminals (EAC and EAC N) for electronic air
cleaner connections are located on the control board. The
terminals provide 115 VAC (1.0 amp maximum) during circu-
lating blower operation. These terminals are energized in
continuous fan mode only if the green wire labeled “G Cool
Speed” is connected as described below. A high voltage con-
nection lead is routed to the junction box for easy connection.
Humidifier Connection
Two 1/4” spade terminals (HUM and HUM N) for humidifier
connections are located on the control board. The terminals
provide 115 VAC (1.0 amp maximum) during heating system
operation. A high voltage connection lead is routed to the
junction box for easy connection.
OPERATION AND MAINTENANCE
SEQUENCE OF OPERATION
The following describes the sequence of operation of the fur-
nace as it relates to a furnace equipped with a variable speed
blower. Refer to the schematic wiring diagram on page 26 for
component location.
CONTINUOUS BLOWER
There are two modes of continuous blower operation. In one
mode the blower is controlled directly through the blower
motor. In the second mode the blower is controlled through
the ignition control. In the first mode, when the thermostat
fan-switch is set to the ON position a circuit is completed
between terminals “R” and “G” of the thermostat. The contin-
uous fan speed will be 63% of the high cool speed. If more air
is desirable the green wire labeled (G Cool Speed) may be
connected to the “G” terminal of the ignition control to achieve
HIGH COOL speed (DIP switch number 3 on the ignition con-
trol must be in the OFF position).
Intermittent Blower Cooling
On cooling/heating thermostats with fan switch, when the fan
switch is set in the auto position and the thermostat calls for
cooling, a circuit is completed between the R, Y and G termi-
nals. The motor is energized through the Y1 cool terminal
and runs on the speed selected on the CFM / Timer board.
The fan off setting is fixed at 60 seconds for SEER enhance-
ment.
HEATING OPERATIONAL SEQUENCE
Two Stage Thermostat
The ignition control in this furnace is unique to this product.
The control allows for a 24 volt or a 115 volt circulator input/
output. This allows for the replacement of the variable speed
motor with a multi-speed PSC motor in the event a variable
speed motor is not available at the time of servicing.
In a typical system, a call for first stage heat is initiated by
closing the W1 thermostat contacts. The inducer blower is
energized at high speed and the control waits for the low
pressure switch contacts to close. The inducer blower is
energized at low speed and the 120 VAC silicon carbide igni-
tor is powered.
At the end of the ignitor warmup time, the first stage of the
two stage gas valve is energized (low fire). Flame must be
detected within 7 seconds. If flame is detected, the delay-to-
fan-on period begins. After the delay-to-fan-on period ends,
the circulator fan is energized at low heat speed and the air
cleaner and humidifier are energized.
A call for second stage heat (W1 and W2) after a call for first
stage heat will energize the inducer at high speed and ener-
gize the circulator at high heat speed. The circulator will ener-
gize at high heat speed after 30 seconds with a call for
second stage heat. If the furnace has been operating in first
stage heat for more than 30 seconds and the control receives
a call for second stage heat, the blower will immediately
switch to high speed. The second stage pressure switch con-
tacts will close and energize the second stage gas valve (high
fire).
If a call for second stage heat occurs at the same time as a
call for first stage heat, the second stage heat is energized
immediately after flame rectification is sensed on fist stage.
When the second stage of the thermostat is satisfied, the
inducer motor is reduced to low speed and the 2nd stage gas
valve is de-energized to 1st stage. The circulator remains on
high heat speed for 30 seconds then de-energizes to low
heat speed.
FIGURE 14 :
Accessory Connections
115 VOLT
HUMIDIFIER
115 VOLT
ELECTRONIC
AIR CLEANER
BLK
WHT
EAC HOT
HUM. HOT
BLK
WHT
EAC
HUM
EAC
HUM
NEUTRALS
SWITCHED
CIRCUITS
Label all wires prior to disconnecting when servicing
controls. Wiring errors can cause improper and dan-
gerous operation. Verify proper operation after ser-
vicing.
