Reznor ADFH Operation Manual - Manual (Page 16)

Form O-ADF/RDF, P/N 148385R2, Page 16
3.0 Operation
and Service
(cont'd)
Function: The potentiometer is a manually set switch
that operates either the discharge damper (Option
AR19) or the return air damper (Option AR22) provid-
ing a mixture of return and outside air. It is a remotely
located switch that requires manual adjustment.
Service: If the potentiometer does not function prop-
erly, replace it with an identical switch.
Description/Function: The pressure null switch is a diaphragm operated differential
pressure switch used in makeup air applications to automatically control building pres-
sure. It maintains a selected positive or negative pressure setpoint by changing the
amount of outside air being introduced to the building through modulating outside air
damper. 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 (caus-
ing the bypass return air damper to go toward the closed position). Conversely, as less
pressure is required, the switch drives the outside air damper in the opposite direction.
Service: Clean the tubing and the screened ends of the pressure tap vents. Be sure
that the switch is installed with the diaphragm in a vertical plane and that the pressure
taps are sheltered from the wind. For further service, follow the manufacturer's instruc-
tions included with the switch.
Pressure Null Switch
(automatic building
pressure sensor)
FIGURE 31 -
Potentiometer,
P/N 16110
Potentiometer
FIGURE 33 -
Photohelic
Pressure Sensor,
P/N 159893
Photohelic Pressure
Switch (automatic
building pressure
sensor)
Description/Function: The photohelic pressure switch is a phototransister relay oper-
ated positive pressure switch used in makeup air applications to automatically control
building pressure. It maintains a selected positive pressure setpoint by changing the
amount of outside air being introduced to the building through a modulating outside air
damper. As more pressure is required in the building, the switch activates the damper
motor driving the outside air damper towards the full open position (causing the bypass
return air damper to go toward the closed position). Conversely, as less pressure is
required, the switch drives the outside air damper in the opposite direction.
Service: Clean the tubing and the screened ends of the pressure tap vents.
If the interior of the switch is protected from dust, dirt, corrosive gases and fluids, years
of trouble-free service may be expected. Zero adjustment should be checked and reset
occasionally to maintain accuracy; follow the manufacturer's instructions included with
the switch.
There are no field-repairable parts in this switch. If the switch should require repair,
contact either the system or the switch manufacturer concerning switch replacement
or repair.
FIGURE 32 -
Pressure Null
Switch, P/N 88052
3.7 Inlet Air Controls
(cont'd)
3.8 Other Optional
Controls
Outside Air Cutoff Control (Option BN2)
Location: The control is in the electrical box (FIGURE 9.); the sensor is in the air inlet.
Function: After sensing pilot flame, the burner ignites at its lowest input rate. The
"amount of heat" required to reach the desired discharge temperature also depends
on the temperature of the incoming outside air. The outside air control is factory set at
60°F (adjustable 25-250°F). The burner reacts differently depending on the entering air
temperature and the setting on the outside air control. The burner --
• may not ignite (pilot valve will not open);
If the actual temperature of the outside air is above the setpoint on the outside air
control, the burner will not ignite.
• may modulate to satisfy discharge setting;
• would shutdown completely only on Option BN2 control, once burner has been fired;
or
Modulating operation will depend on the temperature rise between the outside air
and the discharge air setting.
• may remain on continuous low fire.
If the outside air control is set too high, the burner will continuously burn on low fire
as long as the control switch is set to "winter".
When the outside air control is set properly for the climate, the system blower will con-
tinue to provide the required makeup air (ventilation) at the ambient outdoor tempera-
ture (burner not operating) even when the control switch is set to "winter".
Service: If the control does not function properly, replace it with an identical switch.
FIGURE 34 -
Outside Air Cutoff
Control, P/N 126170