1103UDSA-2--EN, Pag. 32/36
23. Limit
controls
If a limit control needs re-
placing, use only the factory
authorized replacement part
for the size of heater.
For approximate limit loca-
tions, see fi gure 11a..
22. Combustion
air pressure
switch
See fi gure 10, for location. If it
is determined that the pressure
switch needs replacing, use only
the factory-authorized replace-
ment part that is designed for the
model and size of heater being
serviced.
Figure 24
Figure 25 : LC1
Figure 26 : LC3
Figure 27 : Fan control (KFC)
Warning :
Never bypass the limit
controls, hazardous
conditions could result.
The combustion air pressure switch ensures that proper combustion airfl ow is
available. The switch senses the differential pressure between the negative pressure
in the fl ue gas collector box and the pressure in the control section. (For switch
location, see fi gure 11b).
On startup when the heater is cold, the sensing pressure is at the most negative
level, and as the heater and fl ue system warm up, the sensing pressure becomes
less negative.
If a restriction or excessive fl ue pipe length causes the sensing pressure to be below
the allowable level, the pressure switch will shut off the main burner.
DANGER : Safe operation
of this unit requires proper
venting fl ow. Never bypass the
combustion air pressure swtich
or attempt to operate the unit
without the venter operating.
All units are equipped with temperature activated limit controls. The controls are
factory set and non-adjustable. If either setpoint is reached, the corresponding
limit control will interrupt the electric power to the gas valve. These safety devices
provide protection in the case of motor failure or lack of airfl ow due to restrictions.
(For locations, see fi gure 11a.)
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