Reznor RXH (Outdoor PreevA) Unit Installation Manual - Manual (Page 29)

Form I-RDH/REH/RHH/RXH (12-14), P/N 215210 R14, Page 29
The pressure null switch used in Option GE15 is a Dwyer #1640-0 with a range of .01-
.20” w.c. It is shipped separately for field installation. Refer to the following paragraphs
and the manufacturer’s installation instructions included with the switch.
Description and Application - The pressure null switch is a diaphragm operated dif-
ferential pressure switch used in makeup air applications to control building pressure.
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.
Pressure Null Switch
(Field installed to
control Outside Air
Dampers in Option
GE15)
Pressure Null Switch
Installation Instructions
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 securely with the diaphragm in a
vertical plane to ensure proper operation.
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.
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 23 - Pressure Null Switch
(used with Inlet Air Option GE15)
Pressure Null
Switch, P/N 88052
Enthalpy Sensor(s)
- Field installed to
control dampers in
economizer Options
GE21 and GE22)
Option GE21 requires installation of one sensor; Option GE22 requires installation of
two sensors. A system with Option GE21 includes one field-installed parts bag. A sys-
tem with Option GE22 includes two field-installed parts bags. Locate the parts bag(s)
shipped inside the unit. Check components against the list below.
TABLE 20 -
Components in each
Enthalpy Sensor
Parts Bag, P/N 220686
(Option GE21 requires
one parts bag; Option
GE22 requires two.)
Qty Component Description P/N
1 Enthalpy Sensor, Honeywell #C7400A1004 196290
1 Blue Wire Assy, 18 ga x 72” with terminals 220621
1 Purple Wire Assy, 18 ga x 72” with terminals 220620
2 Screws, #6 x 3/4” long 110650
2 5/8” Strain Relief, Heyco #SR6N-4 100392
4 Stick-on Wire Retainers, Cable Fast-Fastex
#8511-29-00
142678
2 Plastic Wire Ties 20913