Reznor ADFH Operation Manual - Manual (Page 10)

Form O-ADF/RDF, P/N 148385R2, Page 10
3.0 Operation
and Service
(cont'd)
• High Airflow Switch
Function: The high airflow switch is a velocity pressure switch that monitors airflow
across the burner. If the high airflow switch senses air velocity above the prescribed
limit, it will shutdown gas flow to the burner. High pressure switch is normally closed; it
opens when pressure rises above .75" w.c. Do not alter or adjust setting.
Low and High Airflow Sensing Pressure Check: (requires slope gauge, several feet
of 1/4" OD tubing and two 1/4" OD barbed tees.)
Attach a slope gauge (0 to 1.0" scale) to the tubing connections in the control com-
partment. The two connections are located below the electrical control box. Remove
the caps on the 1/8" NPT test connections and attach the slope gauge. (The recom-
mended method for attaching the slope gauge is to use field-supplied 1/8" female NPT
x 1/4" O.D. barbed hose connections.)
A) If the system includes an optional discharge damper, before measuring burner
differential air pressure, check to be sure that the damper is fully open.
B) With the blower operating, the pressure differential on the slope gauge should
read between -.25" and -.75" w.c. If the slope gauge reading is within those limits,
no adjustments are necessary. If pressure reading is not within limits, consult the
factory.
C) When air pressure is within the proper range, turn the disconnect switch OFF.
Disconnect the manometer and the slope gauge. Replace the caps removed to
connect the slope gauge.
Pressure Switches and Bypass Damper Airflow (Applies to Model RDF system
with Air Control Option AR19, AR20, AR22, AR23, AR32, AR33, AR34, AR36, or
AR37)
Adjustment of the bypass damper is controlled by the same low and high pressure
switches described above. With a bypass damper, the volume of outside air supplied to
the building is controlled by a manually set potentiometer (Option AR19 and AR22) or
automatically by a pressure null switch (Option AR20 or AR23), a photohelic pressure
switch (Option AR36 or AR37), or a field-supplied computer signal (Option AR33 or
AR34). With Options AR19, AR20, AR33, and AR36 the supply air is varied by adjust-
ing the position of a damper at the blower discharge. With Options AR22, AR23, AR34,
and AR37, a return air damper is adjusted to vary the volume of return air. The unit is
arranged so that a fixed amount (20%) of the rated volume flows over the burner at
a constant velocity. The remainder (80%) of the rated air volume flows either through
a balancing bypass damper or a combination of bypass and return air dampers. As
the supply air volume is varied by the return air or discharge damper, the balancing
damper is adjusted to maintain the required air velocity over the burner. See Paragraph
3.7 for information about inlet air control options.
Service: If the pressure check determines that an airflow switch is not functioning
properly, the switch cannot be serviced and must be replaced with an identical replace-
ment. Low air pressure switch is P/N 203932; high air pressure switch is P/N 203933..
FIGURE 16 -
Ignitor, P/N
121865, and
Flame Sensor,
P/N 134706, on
the Burner
Location: Ignition Controller Module in the Control Compartment Electrical Box (See
FIGURES 9 and 15.); Ignitor and Flame Sensor on the Burner (See FIGURE 16.)
Ignitor
Flame Sensor
Pilot Plate Assy
FIGURE 15 -
Ignition
Control
Module in
the Electrical
Compartment,
P/N 157953
3.5 Ignition System
Hot Surface Ignition
System with Prepurge
Time Delay and Flame
Sensor with Lockout
FIGURE 14 - Air
Pressure Switch
3.4 Air Pressure
Switches
(cont'd)
Function: The ignition system including the controller, the hot surface ignitor, and the
flame sensor function to ignite and prove the pilot flame. When there is a call for heat,
the modular ignition controller is energized. When the controller reads 1.4 amps going
to the hot surface ignitor, it opens the pilot valve for a 15-second trial for ignition. After
the pilot flame rod senses pilot flame, the main gas valve is energized.