Reznor RPBL Unit Installation Manual - Manual (Page 29)

Form I-SSCBL/RPBL, P/N 149159 R7, Page 29
It maintains a selected positive or negative pressure setpoint by changing the amount
of outside air being introduced to the building through the modulating outside air damp-
ers. As more pressure is required in the building, the pressure null switch activates the
damper motor driving the outside air damper towards the full open position and the
recirculated air damper towards the closed position. Conversely, as less pressure is
required, the switch drives the dampers in the opposite direction.
Electric Box
Span
Adjust
Screw
Mounting Plate
Pressure Taps
Low
High
Pressure
Adjust Screw
Increasing
Decreasing
Linkage to
Diaphragm
Low
Common
High
Span Adjustment
Span of
floating
contact
Switching action in the pressure null switch
FIGURE 31 - Pressure
Null Switch (used with
Inlet Air Option AR23)
Installation Instructions
for Pressure Null
Switch
The system is equipped with a combination blower/filter cabinet. Filter rack and filters
are optional equipment.
Filters are available in 2", disposable, permanent, or pleated disposable type.
6.3.4 Optional Filter
Rack and Filters -
SSCBL and RPBL
1. Select an indoor location free from excessive vibration where oil or water will not
drip onto the switch and where ambient temperature will be within a range of -30°F
(dry air) to 110°F.
2. Mount the switch with the diaphragm in a vertical plane. The switch is position
sensitive and is calibrated to operate properly when the diaphragm is vertical.
Mount switch securely.
3. Connect the pressure taps on the top of the switch to sources of air pressure
differential. Metal tubing with 1/4" O.D. is recommended, but any tubing system
which will not unduly restrict the air flow may be used. To maintain a positive
building pressure, vent the low pressure tap to the outdoors and allow the
high pressure tap to monitor building pressure. To maintain a negative building
pressure, reverse the functions of the high and low pressure taps. In either case,
be sure that the outdoor vent is protected from the wind and screened from
insects.
4. Adjustment of the Switch - The "HIGH" actuation point of the null switch is
indicated on a calibrated scale secured to the transparent range screw enclosure.
Building pressure is set by turning the adjustment screw. The "Low" actuation point
is set by adjusting the span of the null by turning the span adjustment screw. The
span range is .01" to .03" w.c.
5. See the wiring diagram included with the furnace to make electrical connections.
IMPORTANT: To eliminate shipping damage
to the switch contacts, the manufacturer
reduced the span adjustment to zero before
shipping. The span should be adjusted
prior to using the switch. (If the switch has
been installed, disconnect the vent tube so
that the null switch is in a neutral position.)
Remove the electrical box cover and while
observing the contacts, turn the span
adjustment screw slowly in a clockwise
direction. Continue turning the adjustment
screw until you are able to see gaps
between the common and both the low and
high contacts. A minimum gap provides the
greatest sensitivity. The wider the gap the
lower the sensitivity.
Quantities and Sizes of
Optional Filters
Type/All 2"
SSCBL/RPBL
400; 800; 1200
SSCBL/RPBL
500; 600
SSCBL/RPBL
700; 1050
Disposable
(2) 16 x 16; (1) 16 x 25;
(4) 12 x 25; (4) 12 x 30 (1) 16 x 25; (1) 16 x 20;
(4) 12 x 20; (4) 12 x 25 (2) 16 x 25; (4) 12 x 30;
(4) 12 x 20
Permanent
(2) 16 x 16; (8) 12 x 16;
(1) 16 x 25; (4) 12 x 26 (1) 16 x 20; (4) 12 x 20;
(1) 16 x 25; (4) 12 x 26 (2) 16 x 25;
(8) 12 x 26
Pleated
Disposable
(2) 16 x 16; (4) 12 x 25;
(1) 16 x 25; (4) 12 x 32
(1) 16 x 20; (1) 16 x 25;
(4) 12 x 20; (4) 12 x 25
(2) 16 x 25; (4) 12 x 32;
(4) 12 x 20