Installer’s Information Manual
Page 21
SECTION 8. SEQUENCE OF
OPERATION
HEATING MODE
1. Thermostat calls for heat ("R" and "W" terminals
connected). Fan Timer verifies that burner limits,
primary limit and pressure switch are in normally
closed (NC) position.
2. Draft-inducer relay is energized and draft inducer motor
starts. Pressure switch normally-open contacts close
after a short delay, energizing gas control.
3. Gas control provides power to igniter and pilot valve to
light pilot. After proving pilot flame, the main valve
opens and igniter tu rns off.
NOTE: If the gas control does not sense a pilot flame
within 30 seconds, it will turn off the igniter while continuing
to purge the gas line. After 30 seconds, the igniter will turn
on again. If a pilot is not sensed in the next 30 seconds,
the gas control will turn off for 5 minutes. This sequence
will continue as long as there is a call for heat.
4. Fan Timer energizes main blower in 30 seconds.
5. After thermostat is satisfied, gas control is de-
energized. After a 5 second post-purge, draft inducer
de-energizes and retu rns pressure switch to normally
closed (NC) position.
6. Main blower remains energized for 60 to 180 seconds
depending on heating blower off-delay setting.
NOTE: This furnace will lock-out if the main blower fails in
heating mode. During lock-out, the Fan Timer's diagnostic
light signal will be 4 flashes. The furnace's Fan Timer can
be reset by cycling power to furnace.
NOTE: On each heating cycle, this furnace verifies that the
pressure switch did not stick closed on the previous cycle.
This condition is detected by checking the pressure switch's
normally closed circuit. If the normally closed circuit is
open, furnace will not operate and the Fan Timer's
diagnostic light signal will be 3 flashes.
COOLING MODE
Thermostat calls for cooling ("R", "Y" and "G" terminals
connected). Condensing unit contactor closes, energizing
condensing unit. Fan Timer energizes main blower on
cooling speed after a short delay. After thermostat is
satisfied, condensing unit contactor is de-energized. Main
blower remains energized for 60 seconds.
CONSTANT FAN MODE
Thermostat calls for constant fan ("R" and "G" terminals
connected). Fan Timer energizes main blower on heating
speed.
A call for cooling, while in constant fan mode, causes main
blower to change from heating to cooling speed. Sixty
seconds after the call for cooling mode ends, main blower
changes back to heating speed. A call for heating mode
while in constant fan mode does not effect main blower
operation. The main blower runs constantly on heating
s peed
.
CONTINUOUS LOW-SPEED FAN OPTION
Some models are equipped with a fan timer that allows
continuous low-speed fan as an option. When available,
this option can be used to operate the blower on low speed
anytime the blower is not otherwise running on heating or
cooling speed. These models do not have electronic air
cleaner terminals on the fan timer.
To use this option, follow these steps:
1. Disconnect electrical power
2. Remove insulator cap from “CONT” terminal on Fan
Timer.
3. Plug blower low-speed wire (red wire) into “CONT”
terminal.
4. Place insulator cap on “UNUSED MOTOR LEAD”
terminal on Fan Timer.
5. Reconnect power. Motor will start on low speed
immediately.
ELECTRONIC AIR CLEANER OPTION
For models with Electronic Air-Cleaner (EAC) terminals, the
Fan Timer "EAC" terminals are energized with 115 VAC
when the main blower is energized. "EAC" terminals are
1/4 inch quick connect tabs located under breakaway
covers. Use insulated quick connects when connecting to
"EAC" terminals. Limit total "EAC" current plus main blower
current to 15 amps max.
HUMIDIFIER
Fan Timer "HUM" terminals are energized with 115 VAC (1
amp. Max.) when draft inducer is energized. "HUM"
terminals are 1/4 -inch quick connect tabs located under
breakaway covers. Use insulated quick connects when
connecting to "HUM" terminals.
BURNER LIMIT CIRCUIT OPEN
If the burner limit circuit opens: burners turn off, draft
inducer stays on, main blower stays on, there is no 24 volt
power on the "R" terminal and diagnostic light signal is 1
flash.
PRIMARY LIMIT CIRCUIT OPEN
If the primary limit circuit opens: burners turn off, draft
inducer turns off, main blower stays on, there is no 24 volt
power on the "R" terminal and the diagnostic light s ignal is
2 flashes.
VENT LIMIT CIRCUIT OPEN
If vent limit circuit opens: burners turn off, draft inducer runs
during call for heat, and main blower turns off after blower
off-delay. There is 24-volt power on the "R" terminal and no
diagnostic light signal.
