14
SYSTEM OPERATION
T
O
AVOID
PERSONAL
INJURY
OR
DEATH
DUE
TO
ELECTRICAL
SHOCK
,
TURN
OFF
POWER
TO
THE
FURNACE
BEFORE
CHANGING
SPEED
TAPS
.
WARNING
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
HEAT MODE:
Call For 1st Stage Heat
•
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 aux
-
iliary 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:
- Trial for ignition begins.
- 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.
• Retry counter is zeroed, if after 10 seconds the flame
is sensed:
- Control enters normal operating loop where all
inputs are continuously checked.
• After the delay to heat on period, the circulator fan
is energized at the low heat speed.
• The air cleaner will be energized with the circulator.
• If the call for heat is lost while the control is in the
trial for ignition period without flame being detected,
the control will turn off the gas valve and igniter.
The control then enters the post-purge routine. The
post-purge time will be increased to 60 seconds.
After completing the post-purge, the control resumes
normal operation.
CALL FOR 2ND STAGE AFTER FIRST STAGE:
•
The inducer motor is enabled at 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 2nd 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
CALLED:
•
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.
SIMULTANEOUS CALL FOR LOW AND HIGH HEAT
A call for both stages of heat will establish low fire before
going to high fire
Operation Using a Single Stage Heating Thermostat
Using a single stage thermostat, the options for high fire
delay are: 10 minutes; 20 minutes; or auto
•
The automatic second stage logic is a method of
energizing the second stage valve based on the
recent average of the heating duty cycle. During a
typical heating day there will be at least one call for
heat within a 3 hour period, and usually much more
often. During this mode the low to high stage delay
is determined by using the average calculated duty
cycle from the table below. Once the specified de
-
lay time has expired the second stage valve will be
energized
• On the heating cycle following a period of 3 hours
(or greater) in which there is no call for heat, the sec
-
ond stage valve will energize based on the average
calculated duty cycle prior to the three hour no call
for heat. If the average calculated duty cycle is less
than 50%, then the low to high stage delay will be
determined from the table below. In this case, an
assumption is made that the outside temperature is
fairly mild and the long time between calls for heat
was due to a low thermal loss in the building. Going
quickly to second stage heat is not required in this
instance.
