50
6. Make sure there are no cabinet air leaks allowing sup-
ply air to affect combustion
7. If heat exchanger integrity is uncertain, follow proce-
dures in Service Bulletin SF-041
M
EMORY
C
HIPS
Memory chips are a service only item and are not sent out
with new equipment. They are used only in the rare occur-
rence where communicating equipment shared data needs
to be restored.
Memory chips should not be routinely installed at the time
of installation. A memory chip is not required when an indi-
vidual control board or motor is replaced.
A memory chip is only required when all communicating com-
ponents have been replaced with service parts containing
no shared data. If either an existing control board or ECM
motor needed to be replaced, the service part would upload
the necessary data from the remaining communicating com-
ponent. In a fully communicating system, this would include
the communicating thermostat and communicating outdoor
unit control board as the necessary data is stored in all com-
municating devices.
A furnace void of shared data will not function in a legacy or
a fully communicating installation. The furnace display would
show “d0” indicating that there is no shared data in the
furnace control board. If it is ever necessary to use a memory
chip, the specific memory chip for your furnace number must
be used.
To use a memory chip;
1. Power down all HVAC equipment in the system.
2. As when handling any electronic components, discharge
any static electricity you may be carrying by touching
grounded metal.
3. Insert the memory card in the slot on the control board.
4. Power the system back up and allow a few minutes for
the network to establish communication between all de-
vices.
5. Furnace control board will display “OP” or ‘ON” (depend-
ing on board part number).
6. Check operation.
7. Memory chip can be left on the control board (recom-
mended) or removed once equipment is powered down
again.
Safety Circuit Description
A number of safety circuits are employed to ensure safe and
proper furnace operation. These circuits serve to control any
potential safety hazards and serve as inputs in the monitoring
and diagnosis of abnormal function. These circuits are continu-
ously monitored during furnace operation by the integrated con-
trol module.
I
NTEGRATED
F
URNACE
C
ONTROL
(IFC)
The integrated control module is an electronic device which, if
a potential safety concern is detected, will take the necessary
precautions and provide diagnostic information through an LED
display.
P
RIMARY
L
IMIT
The primary limit control is located on the partition panel and
monitors heat exchanger compartment temperatures. It is a
normally-closed (electrically), automatic reset, temperature-ac-
tivated sensor. The limit guards against overheating as a re-
sult of insufficient conditioned air passing over the heat ex-
changer.
A
UXILIARY
L
IMIT
The auxiliary limit controls are located on or near the circulator
blower and monitors blower compartment temperatures. They
are a normally-closed (electrically), auto-reset sensors. These
limits guard against overheating as a result of insufficient con-
ditioned air passing over the heat exchanger.
R
OLLOUT
L
IMIT
The rollout limit controls are mounted on the burner/manifold
assembly and monitor the burner flame. They are normally-
closed (electrically), manual-reset sensors. These limits guard
against burner flames not being properly drawn into the heat
exchanger.
P
RESSURE
S
WITCHES
The pressure switches are normally-open (closed during opera-
tion) negative air pressure-activated switches. They monitor
the airflow (combustion air and flue products) through the heat
exchanger via pressure taps located on the induced draft blower
and the coil front cover. These switches guard against insuffi-
cient airflow (combustion air and flue products) through the
heat exchanger and/or blocked condensate drain conditions.
F
LAME
S
ENSOR
The flame sensor is a probe mounted to the burner/manifold
assembly which uses the principle of flame rectification to de-
termine the presence or absence of flame.
OPERATIONAL CHECKS
