Reznor RPB Unit Installation Manual - Manual (Page 22)

Form I-RPB, P/N 131782 R11, Page 22
6.5 Blowers, Belts,
and Drives
3/4”
(19mm)
FIGURE 25 - Check Belt
Tension
6.0 Mechanical
(cont'd)
6.4 Supply Air
Discharge
(cont'd)
Instructions for Installing Discharge Air Sensor in the Ductwork
FIGURE 24A -
Discharge Air Sensor
Holder, P/N 115850,
used in Makeup Air
Option AG15
Secure sensor in clip.
Position holder so that it
shields sensor from direct
airflow.
FIGURE 24B - A
Discharge Air Sensor
and Mixing Tube are
used in Electronic
Modulation Options
AG8, AG9, and AG39
1. Depending on the option, the sensor will be as shown in FIGURE 24A, in FIGURE
24B, or field-supplied for Option AG40. See Paragraph 3.2 for a list of shipped-
separate components by option code.
2. Determine a location in the ductwork to install the sensor.
Select a location a sufficient distance from the outlet to provide a good mixture of
discharge air temperature. According to the latest edition of AMCA Standard 201,
in straight ducts, the air is typically well mixed a minimum of five equivalent duct
diameters from the discharge of the unit with equivalent duct diameter defined
as equal to the square root of 4AB/3.14. "A" and "B" are the duct cross-sectional
dimensions.
Example: Supply ductwork cross-sectional dimension is
24" x 12" (610mm x 305mm).
5 x
4 x 12 x 24
3.14
= 96" 5 x
4 x 305 x 610
3.14 = 2435mm
Solution: Locate the sensor a minimum of 96" (2435mm)
from the outlet of the unit.
NOTE: If the length of the discharge duct is less than 8 ft (2.4M), a mixing vane is
recommended for mixing the discharge air.
Do not mount the sensor in the ductwork after a split in the supply as that will
cause loss of control in the duct that does not house the sensor.
3. The position of the sensor holder or mixing tube is important. The holder in
FIGURE 24A will extend 9-3/16” (233mm) into the ductwork. The mixing tube in
FIGURE 24B is 12" (305mm) long.
In horizontal ductwork, locate the sensor assembly in the top, middle of the duct
with the sensor probe extending vertically down into the center of the airstream.
In vertical ductwork, locate the sensor assembly in the middle of the side of the
duct that corresponds with the top middle of the discharge outlet.
Turn the holder so that the element will be shielded from direct airflow and will
sense the air temperature as it flows through the holes in the holder.
At the selected location in the ductwork, mark the diamond-shaped hole
[approximately 1” x 1” (25mm x 25mm)] required for the sensor holder or the round
hole needed for the mixing tube. Cut the hole no larger than required.
4. Option AG15 - Push the element into the clip in the holder. Determine where the
sensor wire should enter the box and remove the knockout. Slide the holder into
the ductwork. Using four field-supplied No. 6 sheetmetal screws, attach the box
portion of the holder to the ductwork. Attach a field-supplied cable connector to the
box, connect the sensor wire, and attach the box cover.
Options AG8, AG9, and AG39 - Slide the mixing tube into the ductwork and
attach the sensor. Connect the wires as shown on the wiring diagram.
Option AG40 - Follow the instructions provided with the field-supplied sensor.
Refer to the wiring diagram with the unit and the field-supplied sensor to connect
the wires.
6.5.1 Belts and Belt Tension
Check belt tension. Proper belt tension is important to the long life of the belt and motor.
A loose belt will cause wear and slippage. Too much tension will cause excessive motor
and blower bearing wear. Adjust the belt tension by turning the adjusting screw on the
motor base until the belt can be depressed 3/4" (19mm). (See FIGURE 25.) After cor-
rect tension is achieved, re-tighten the locknut on the adjustment screw. Be sure that
the belt is aligned in the pulleys.
6.5.2 Adjusting Blower Speed
The blower speed may be adjusted to achieve the desired outlet temperature, as long
as the adjustment is within the temperature rise and the static pressure limits shown
on the furnace rating plate. Motors are factory set between maximum and minimum
blower speeds.
If the duct resistance is low, the blower may deliver too high an air volume. If the resis-
tance is very low, the blower may deliver excess air to overload the motor, causing the
6.4.2 Discharge Air
Sensor (cont'd)