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A
L
UXILIARY
IMIT
The auxiliary limit controls are located on or near the circulator
blower and monitors blower compartment temperatures. They
are a normally-closed (electrically), manual-reset sensors. These
limits guard against overheating as a result of insufficient condi-
tioned air passing over the heat exchanger.
R
L
OLLOUT
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
S
RESSURE
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
S
LAME
ENSOR
The flame sensor is a probe mounted to the burner/manifold
assembly which uses the principle of flame rectification to deter-
mine the presence or absence of flame.
T
ROUBLESHOOTING
E
D
LECTROSTATIC
ISCHARGE
NOTE: Discharge body's static electricity before touching unit.
An electrostatic discharge can adversely affect electrical
components.
Use the following precautions during furnace installation and ser-
vicing to protect the integrated control module from damage. By
putting the furnace, the control, and the person at the same
electrostatic potential, these steps will help avoid exposing the
integrated control module to electrostatic discharge. This pro-
cedure is applicable to both installed and uninstalled (ungrounded)
furnaces.
1. Disconnect all power to the furnace. Do not touch the
integrated control module or any wire connected to the
control prior to discharging your body's electrostatic
charge to ground.
2. Firmly touch a clean, unpainted, metal surface of the
furnace away from the control. Any tools held in a person's
hand during grounding will be discharged.
3. Service integrated control module or connecting wiring
following the discharge process in step 2. Use caution not
to recharge your body with static electricity; (i.e., do not
move or shuffle your feet, do not touch ungrounded
(ESD) P
RECAUTIONS
objects, etc.). If you come in contact with an ungrounded
object, repeat step 2 before touching control or wires.
4. Discharge your body to ground before removing a new
control from its container. Follow steps 1 through 3 if
installing the control on a furnace. Return any old or new
controls to their containers before touching any ungrounded
object.
C
F
S
HECKING
LAME
IGNAL
Flame current can be measured in two ways:
1. Putting a D.C. microamp meter in series with the flame
rod
2. Putting a D.C. volt meter across the two solder pads
in the flame current section of the control board.
1 D.C. volt = 1 microamp. See Figure 41.
Flame Current
Solder Pads
L
F
C
IMIT
AULT
ODES
If the control detects the high limit circuit open, the RED
LED will flash FOUR times and energize the inducer and in-
door blower.
If the limit circuit opens five times within a single call for
heat, the furnace will go into lockout for one hour. The RED
LED will display a FOUR flash code during this time. The
control board can be reset by cycling 115 volt power to the
furnace.
51
Figure 41
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Troubleshooting
