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 switches 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 turns 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 returns 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 lockout if the main blower fails in heating mode. During lockout, the Fan Timer's diagnostic light signal will be 4 flashes. The furnace's Fan Timer can be reset by cycling 115-volt 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 mode 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 speed.

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 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 signal is 2 flashes.

Installer’s Information Manual

Page 17