Lennox EL195UHNE Series Manual page 13

7. Combustion Air Inducer (B6) & Cold End Header
Box Figure 8
All EL195UHNE units use a combustion air inducer to
move air through the burners and heat exchanger during
heating operation. The blower uses a shaded pole 120VAC
motor. The motor operates during all heating operation
and is controlled by integrated control A92. Blower oper-
ates continuously while there is a call for heat. The inte-
grated control will not proceed with the ignition sequence
until combustion air inducer operation is sensed by the
proving switches.
The combustion air inducer is installed on the cold end
header box. The cold end header box is a single piece
made of hard plastic. The box has an internal channel
where the combustion air inducer creates negative pres-
sure at unit start up. The channel contains an orifice used
to regulate flow created by the combustion air inducer.
The box has pressure taps for the combustion air inducer
pressure switch hoses. The pressure switch measures the
pressure across the combustion air inducer orifice or dif-
ference in the channel and the box. If replacement is nec-
essary the gaskets used to seal the box to the vestibule
panel and the combustion air inducer to the box, must also
be replaced.
8. Combustion Air Prove Switch Figure 8 and 9
EL195UHNE series units are equipped with a differential
pressure switch located on the cold end header box. The
switch monitors across the combustion air inducer orifice
to insure proper flow through the heat exchanger.
The switch is a SPST N.O. pressure switch electrically
connected to the integrated control. The purpose of the
switch is to prevent burner operation if the combustion air
inducer is not moving enough air for proper combustion.
COMBUSTION AIR INDUCER AND PROVE SWITCH
Combustion Air Inducer
FIGURE 8
Prove Switch
Page 13
Pressure Switch
FIGURE 9
On start-up, the switch monitors whether the combustion
air inducer is operating. It closes a circuit to the integrated
control when the difference in pressure across the com-
bustion air inducer orifice exceeds a non-adjustable facto-
ry setting. If the switch does not successfully sense the re-
quired differential, the switch cannot close and the furnace
cannot operate. If the flue or air inlet become obstructed
during operation, the switch senses a loss of pressure dif-
ferential and opens the circuit to the integrated control. If
the condensate line is blocked, water will back up into the
header box and reduce the pressure differential across
the switch. The pressure switch opens if the differential
drops below the set point. See table 7.
TABLE 7
Unit
040
060
080
100
Setpoint
0.50"