Haier GE APPLIANCES NF80D045S3A Service Manual page 14

Combustion Air Inducer (B6)
All NF80DS units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation. The blower uses a 120VAC motor. The motor
operates during all heating operation and is controlled
by integrated control A92. The inducer also operates for
15 seconds before burner ignition (pre-purge) and for 5
seconds after the gas valve closes (post-purge).
A pressure switch mounted on the combustion air inducer
orifice plate is used to prove inducer operation. The
combustion air inducer orifice will be different for each
model. The switch monitors air pressure in the inducer
housing. During normal operation, the pressure in the
housing is negative. If pressure becomes less negative
(signifying any obstruction in the flue) the pressure switch
opens. When the pressure switch opens, the integrated
control (A92) immediately de-energizes the gas valve to
prevent burner operation.
Combustion Air Inducer Pressure Switch (S18)
NF80DS series units are equipped with a combustion air
pressure switch located on the combustion air inducer
orifice bracket. The switch is connected to the combustion
air inducer housing by means of a flexible silicone hose.
It monitors negative air pressure in the combustion air
inducer housing.
The switch is a single-pole single-throw proving switch
electrically connected to the furnace control. The
purpose of the switch is to prevent burner operation if
the combustion air inducer is not operating or if the flue
becomes obstructed.
MULTI−METER
SET TO MEASURE OHMS
On start-up, the switch senses that the combustion air
inducer is operating. It closes a circuit to the integrated
control when pressure inside the combustion air inducer
decreases to a certain set point. Set points vary depending
on unit size. See Table 6. The pressure sensed by the
switch is negative relative to atmospheric pressure. If
the flue becomes obstructed during operation, the switch
senses a loss of negative pressure (pressure becomes
more equal with atmospheric pressure) and opens the
circuit to the integrated control and gas valve. A bleed port
on the switch allows relatively dry air in the vestibule to
purge switch tubing, to prevent condensate build up.
The switch is factory set and is not field adjustable. It is a
safety shut-down control in the furnace and must not be
bypassed for any reason. If switch is closed or by-passed,
the integrated control will not initiate ignition at start up.
Unit
045
070
090
110
Troubleshooting
See Figure 9 for measuring operating pressure and
checking resistance in the pressure switch.
To Pressure Switch
-
+
Figure 9.
Page 14
Break ± 0.05
(in. w.c.)
-0.60
-0.65
-0.60
-0.65
Table 6.
Remove tubing from CAI and
insert "Tee" and additional tubing.
Field Provided
Tubing To CAI Port
High
or
Low
31-5000736 Rev. 0