33
Upon power up, all segments in the dual seven segment
display will illuminate briefly and then display ON, indicat-
ing the furnace is standing by & ready to receive commands
from the thermostat. Once a call for heat is received by the
furnace control board, the furnace will enter a “calibration
routine” The calibration routine allows the furnace to adapt
to the installed venting and combustion air piping. The in-
ducer will ramp up and down momentarily to determine what
the closing points and opening points of the pressure switches
are compared to inducer RPM. The calibration routine is
described in detail on page 43. The illustrations following
show firing rates with 24 volt legacy thermostats as well as
with communicating thermostats.
Modulating furnaces light off at 80% firing rate. The dual
seven segment display will alternate showing:
1.
Current Operating Mode; H = legacy or communicat-
ing call for heat
C = communicating call for cooling, C1 / C2 legacy call
for cooling (Y + G + O)
P1 / P2 = legacy call for heat - heat pump (Y + G)
F = call for constant fan
2.
Gas heat firing rate % (35% - HI 100%)
3.
A = (demand for supply air)
4.
Air Quantity (Single or double digit displayed = CFM X
100)
MIN.
57%
78%
(80%)
100%
IGNITION
UNIT CALL FOR HEAT ENDS
10 MINS.
8 MINS.
2 MINS.
Operation with Conventional 1-Stage Thermostat
(DIP switch selections 1-Stage heat)
Call for heat, thermostat energizes W1 on IFC (W2 input is
ignored).
After a successful Light Off Sequence and expiration of the
Ignition Stabilization Period:
•
After 2 minutes, the IFC increases to 57% at a rate of
1% per second
•
After 10 total minutes, the IFC increases to 78% at a
rate of 1% per second.
•
After 20 total minutes, the IFC increases to 100% at a
rate of 1% per second for the remainder of the call for
heat.
•
The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
MIN.
50%
60%
(80%)
70%
IGNITION
10 MINS.
8 MINS.
2 MINS.
Operation with Conventional 2-Stage Thermostat
(DIP switch selects 2-stage heat)
Call for 1st-Stage Heat - Thermostat contacts close R to W1.
After a successful Light Off Sequence and expiration of the
Ignition Stabilization Period:
•
The IFC adjusts to the low firing rate.
•
After 2 minutes, the IFC increases to 50% fort he
next 8 minutes.
•
Thereafter, the IFC will increase 10%, at a rate of 1%
per second, every 10 minutes for the remainder of
the call for heat (See above figure).
•
The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
OPERATION
