Tempstar F97CMN Installation, Start-Up, Operating And Service And Maintenance Instructions page 69

F97CMN and G97CMN: Installation, Start-up, Operating and Service and Maintenance Instructions
control CPU will lock out of Gas-Heating mode and operate the
inducer motor IDM at full speed until flame is no longer proved.
5. Inducer Speed Change - If the cycle starts in intermediate-heat,
the furnace control CPU reduces the inducer speed slightly after
flame sense. If cycle starts in maximum-heat, the furnace control
CPU increases the inducer speed after flame sense.
6. Blower-On delay — If the burner flame is proven, the blower-ON
delay for intermediate-heat and maximum-heat are as follows:
Intermediate-heat - 45 seconds after the gas valve GV (pin 5) is
opened the blower motor BLWM is turned ON at the modulating
heat airflow.
Maximum-heat - 25 seconds after the gas valve GV (pin 5) is
opened the BLWM is turned ON at maximum-heat airflow.
Simultaneously, the humidifier terminal HUM and electronic air
cleaner terminal EAC-1 are energized and remain energized
throughout the heating cycle.
7. Switching from Intermediate-Heat to a Low Range Input - If
the furnace control CPU switches from intermediate-heat to a low
range input (low range input is an input rate less than or equal to
51% of full rate), the furnace control CPU will turn the blower ON
or switch to the modulating heat airflow, energize the PSR relay to
open the NC contact, and slowly decrease the inducer motor speed
to the desired inducer RPM.
Switching from a Intermediate-Heat to a Medium Range Input
- If the furnace control CPU switches from intermediate-heat to a
different medium range input (medium range input is an input rate
between 52% and 71% of full rate), the furnace control CPU will
turn the blower ON or switch to the modulating heat airflow, and
continue to maintain the inducer motor speed or change it further if
required.
Switching from a Intermediate-Heat to a High Range Input - If
the furnace control CPU switches from intermediate-heat to a high
range input (high range input is an input rate greater than or equal to
72% of full rate), the furnace control CPU will turn the blower ON
or switch to the modulating heat airflow, and increase the inducer
motor speed to the desired inducer motor RPM.
Switching from Low Range Input to Maximum-Heat - If the
furnace control CPU switches from a low range input to
maximum-heat, the furnace control CPU will de-energize the PSR
relay to close the NC contact and slowly increase the inducer motor
speed until the medium pressure switch MPS closes. When the
medium pressure switch MPS closes the inducer motor RPM is
noted by the furnace control CPU. The RPM is used to evaluate
vent system resistance. This evaluation is then used to determine
the required RPM necessary to operate the inducer motor at
maximum-heat. The blower motor BLWM will transition to
maximum-heat airflow five seconds after the furnace control CPU
switches from a low range input to maximum-heat. As the inducer
RPM increases, the high pressure switch HPS should close.
Switching from Medium Range Input to Maximum-Heat - If the
furnace control CPU switches from medium range input to
maximum-heat, the furnace control CPU will increase the inducer
motor speed to the maximum-heat inducer motor RPM. The blower
motor BLWM will transition to the maximum-heat airflow five
seconds after the furnace control CPU switches from a medium
range input to maximum-heat. As the inducer RPM increases, the
high pressure switch HPS should close.
8. Blower-Off Delay — When the thermostat is satisfied, the R to W
circuit is opened, de-energizing the gas valve GV (pin 5), stopping
gas flow to the burners, and humidifier terminal HUM. The inducer
motor IDM will remain energized for a 15-second post-purge
period. The blower motor BLWM and air cleaner terminal EAC-1
will remain energized at minimum-heat airflow or transition to
minimum-heat airflow for 90, 120, 150, or 180 seconds (depending
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
on selection at blower-OFF delay switches). The furnace control
CPU is factory-set for a 120-second blower- OFF delay.
Two-Stage Thermostat and Modulating Heating
(Adaptive Mode)
Operation of Modulating Heating (Adaptive Mode; SW1-2 and SW4-2
are both OFF) with a two-stage thermostat is the same as with a
single-stage thermostat, EXCEPT for the following:
If the two-stage thermostat R-W2 circuit closes along with the R to
W/W1 circuit, while the furnace is operating at any capacity less than
maximum, the furnace will switch to the maximum heating capacity. At
this point, the furnace control heating algorithm is overridden and the
two-stage thermostat takes control of staging until BOTH R to W/W1
and R to W2 circuits are opened.
The furnace with transition back to the lower heating capacity if the
two-stage thermostat opens the R-W2 circuit, but leaves R to W/W1
circuit closed. The furnace control will continue to follow the commands
from the two-stage thermostat for W/W1 and W2, until the R to W/W1
circuit is opened.
After the two-stage thermostat opens both the R to W/W1 and R to W2
circuits, the adaptive algorithm will set the beginning capacity of the
next heating cycle to the same value as the heating cycle that most
recently completed.
Two-Stage Thermostat and Two-Stage
Minimum/Maximum Heating
See Fig. 36 for thermostat connections.
NOTE: In this mode, the minimum-heat only switch SW1-2 must be
ON to select the minimum-heat only operation mode in response to
closing the thermostat R to W1 circuit. Closing the thermostat R to
W1-and-W2 circuits always causes maximum-heat operation, regardless
of the setting of the minimum-heat only switch.
The furnace will start up in either intermediate-, or maximum-heat. The
furnace will operate in minimum-heat after starting and operating for 1
minute at intermediate-heat before transitioning to minimum-heat.
The wall thermostat "calls for heat", closing the R to W1 circuit for
minimum-heat or closing the R to W1-and-W2 circuits for
maximum-heat. The furnace control performs a self-check, and verifies
the low, medium and high pressure switch contacts LPS, MPS and HPS
are open, then de-energizes the PSR relay to close the NC contact.
The start up and shut down functions and delays described above apply
to the 2-stage minimum/maximum heating mode as well, except for
switching from maximum- to minimum-heat.
9. Switching from Maximum- to Minimum-Heat - If the thermostat
R to W2 circuit opens, and the R to W1 circuit remains closed, the
furnace control CPU will gradually decrease the inducer motor
speed to the required intermediate-heat RPM. When the inducer
motor IDM reduces pressure sufficiently, the high pressure switch
HPS will open and the gas rate will be changed to
intermediate-heat. The gas valve solenoid GV (pin 5) will remain
energized as long as the low pressure switch LPS remains closed.
When the inducer motor speed gets within 15% of the required
intermediate-heat RPM the furnace control CPU will start a 5
second blower airflow change delay. After the 5 second blower
airflow change delay is completed the blower airflow will transition
to minimum-heat airflow. At this point the furnace control CPU
will energize the PSR relay to open the NC contact and slowly
decrease the inducer motor speed to the required minimum-heat
RPM. When the PSR relay is energized and the NC contact opens
the furnace control CPU will reduce the gas rate to minimum-heat
RPM.
69