18
Step 1 Mount Pressure Tap
Using the factory provided bracket, mount the
pressure tap to the outside of the unit. Choose a
location out of the prevailing winds and away from
supply or exhaust fans to assure accurate readings.
See figure #35
Step 2 Run Pressure Tap Lines
A pressure tap line must be run from the pressure tap
mounted on the outside of the unit to the low
pressure tap on the back of the photohelic gauge (see
figure #36). A second pressure tap line must be run
from the high pressure tap on the back of the
photohelic to the space. The high pressure line must
be run even if the photohelic is mounted in the space.
Fifty feet of tubing is supplied with the unit.
Step 3 Set the Building Pressure
The pressure gauge (see figure #37) is used to set the
desired building pressure. The pressure is set by
adjusting the knobs for the upper and lower pressure
limits. Typical settings are 0.0 in. wc for the lower and
0.10 in. wc for the upper pressure setting.
Step 4 Check Control System
Before the unit is left in service, the recirculation
control system should be tested. This can be
accomplished by turning both knobs to the upper
most pressure setting. You may have to remove the
outdoor pressure tap tubing. The return air damper
should close (VAV systems should go to max speed).
Then set both knobs at the lowest setting, and the
damper should open (VAV systems should go to
minimum speed). It may take one to two minutes for
the damper to reach the desired position. Reset the
correct pressure limits before starting the unit. The
picture on the bottom right shows a typical photohelic
setting. The needle in this photo indicates a negative
building pressure. During correct operation the
indicating needle will remain between or near the
setting needles.
Installation - Building Pressure Control (Optional)
Low Pressure Tap
To Outside
High Pressure Tap
To Space
Factory
Wiring
Pressure Setting Knobs
Pressure Setting
Needles
Pressure Indicating
Needle
Installation
NOTE!
Blower start-up (S-1), steps 1-4 should be
performed before the blower is run.
Figure 35.
Pressure Tap
Figure 36.
Pressure Tap Connections
Figure 37.
Building Pressure Settings