48
NORMAL SEQUENCE OF OPERATION
Power Up
•
When power is supplied, the control will energize the
Red LED, microcomputer runs its self-check routine.
• The control will check the status of the gas valve
circuitry.
•
Line polarity is checked.
•
The control then enters standby waiting for a call for
heat or cool.
•
The Furnace status LED will display a slow green
flash signaling standby mode.
Heating Mode
Call for 1st Stage Heat Only:
•
On a call for first stage heat, the thermostat contacts
close signaling the control module.
•
The microcomputer runs its self-check routine.
•
The Amber LED will display a slow flash signaling
normal heat operation.
•
The control module checks the high limit (and/or
auxiliary limit) switch(es) for normally closed contacts.
• The control checks the low pressure switch for a
shorted condition
•
The gas valve relay status is checked for proper
operation. Once the low pressure switch is detected
open, the inducer blower is energized at high speed
and the humidifier is enabled.
•
The low pressure switch is checked for closure.
•
Once the low pressure switch is closed, the pre-purge
period begins. The inducer will be energized at high
speed for the pre-purge period.
•
Following the completion of pre-purge, the inducer
switches to low speed and the igniter warm up period
begins.
•
After completion of the igniter warm up period:
a. Trial for ignition begins.
b. The first stage of the gas valve is energized.
•
The igniter is de-energized when flame is sensed or at
the conclusion of the ignition activation period (IAP),
whichever comes first.
•
When flame is sensed, the delay to heat on period
begins timing.
•
After the delay to heat on period, the circulator fan is
energized at the low heat speed.
•
The EAC contact is energized with the circulator.
Call for 2nd Stage After First Stage:
•
The inducer motor goes to high speed.
•
The pressure switches are checked for closure.
Closure of the second stage pressure switch will
energize the high fire stage of the gas valve.
•
The high speed circulator output is energized.
•
NOTE:
A call for 2
nd
stage without a call for 1st stage
will be ignored, and a three amber flash code will be
displayed on the LED. This error code will only be
stored in memory once during a single power cycle.
2nd Stage Satisfied, First Stage Still Calling:
•
When the second stage of the thermostat is satisfied,
the inducer blower is reduced to low speed which de-
energizes the second stage of the gas valve.
•
After the high heat off delay expires, the circulator is
reduced to low heat speed.
• NOTE:
A call for second stage without a call for first
stage will be ignored.
Cooling Mode
Low stage cooling Mode sequence:
•
On a call for lo cool, the YLO and G thermostat
contacts close signaling the control module.
•
The LED will display a “GREEN”1 flash
•
The compressor and condenser fan are energized.
The compressor is connected to the YLO terminal of
the control module.
•
The circulator fan is energized at lo cool speed after
a cool on delay. The electronic air cleaner will also be
energized.
•
After the thermostat is satisfied, the compressor is
de-energized and the 45 second fan off delay period
begins.
•
Following the 45 second cool mode fan off delay
period, the cool circulator and air cleaner relay are de-
energized.
Single cooling stage thermostat or 2
nd
stage cooling
Mode sequence:
•
On a call for cool, the Y and G thermostat contacts
close signaling the control module.
•
The LED will display a “GREEN”2 flash
•
The compressor and condenser fan are energized.
The circulator fan is energized at cool speed after a
cool on delay. The electronic air cleaner will also be
energized.
•
After the thermostat is satisfied, the compressor is de-
energized and the fan off delay period begins.
•
Following the 45 second fan off delay period, the cool
circulator and air cleaner relay are de-energized.
Note: If a call for both YLO and Y are present, Y
will have priority.
Fan Only Mode
MANUAL FAN ON:
•
Call for continuous fan (24 volts on the furnace “G”
terminal.)
•
The LED will display rapid “GREEN”.
•
The circulator blower and the electronic air cleaner
terminal are energized.
