40
MIN.
50%
60%
(80%)
70%
IGNITION
10 MINS.
8 MINS.
2 MINS.
90%
Operation with Conventional 2-Stage Thermostat
(DIP switch selects 2-stage heat)
Figure 47
Call for 2nd-Stage Heat - Thermostat contacts close R to W1
and W2.
After a successful Light Off Sequence and expiration of
the Ignition Stabilization Period:
•
The furnace control board adjusts to the low firing
rate of 35%.
•
After 2 minutes, the furnace control board
increases the firing rate to 80%.
•
Thereafter, the IFC will increase the firing rate
by 10%, at a rate of 1% per second, every 10
minutes for the remainder of the call for heat.
•
The circulator fan is adjusted to the appropriate
CFM, corresponding to the current firing rate.
Call for 2nd-Stage Heat with 1st-Stage call for heat call in
progress, with conventional 2-Stage Thermostat.
•
The furnace control board increases the firing rate
to 100% at a rate of 1% per second for the
remainder of the W2 call.
•
The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
MIN.
50%
78%
(80%)
100%
IGNITION
2 MINS.
CALL FOR
2ND STAGE HEAT
UNIT CALL FOR HEAT ENDS
Figure 48
Call for 2nd-Stage Heat satisfied; Call for 1st-Stage Heat
remains.
•
The furnace control board remains at the current
firing rate until the 1st-Stage call for heat is
satisfied.
H
EATING
O
PERATION
WITH
CTK01 T
HERMOSTAT
(C
OMMU
-
NICATING
)
•
When the Thermostat Heat Setup DIP switch is
set to 2-Stage heat, the furnace control board
operation will be compatible with a CTK01
communicating thermostat.
•
When a call for heat is sent, the furnace will go
through the Light Off Sequence, at which time
the Heat Current Demand Status will still show
0%. After the successful Light Off Sequence and
expiration of the Ignition Stabilization Period:
•
The furnace control board adjusts to the low firing
rate.
•
After 2 minutes, the furnace control board accepts
the specific heat requested demand.
•
If the differential is equal to or less than 2 degrees,
the furnace control board will follow the
conventional 2-Stage algorithm, equivalent to a
W1 request and be reflected in the heat current
demand status %.
•
If the heat differential is greater than 2 degrees,
the furnace control board will follow the
conventional 2-Stage algorithm, equivalent to a
W2 request and be reflected in the heat current
demand status %.
•
The circulator will operate per the heat airflow
profile.
H
EATING
O
PERATION
WITH
CTK02**, CTK03** &
CTK04** T
HERMOSTAT
(M
ODULATING
C
OMMUNICATING
)
•
When the Thermostat Heat Setup DIP switch is
set to 1-Stage heat, the furnace control board
operation will be compatible with a modulating
communicating thermostat (CTK02**, CTK03 or
CTK04).
•
When a call for heat is sent, the furnace will go
through the Light Off Sequence, at which time
the Heat Current Demand Status will still show
0%. After the successful Light Off Sequence and
expiration of the Ignition Stabilization Period:
•
The furnace control board adjusts to the low firing
rate.
•
After 2 minutes, the furnace control board accepts
the specific Heat Requested Demand.
•
If the differential is 2 degrees or less, the heat
current demand status will show 50%.
