Thomas & Betts RZ-NA 441-OMS Inlet Air Controls contd, Photoelectric Smoke Detector Option SA1

Figure 26 -

Photohelic

Pressure

Sensor,

P/N

159893

14.Inlet Air Controls (cont'd)

Pressure Null Switch (cont'd)

building pressure. 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 (causing the bypass return air damper to go toward the closed posi- tion). 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 instructions included with the switch.

Photohelic Pressure Switch (automatic building pressure sensor)

Description/Function: The photohelic pressure switch is a phototransister relay operated 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). Con- versely, 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 adjust- ment should be checked and reset occasionally to maintain accuracy; follow the manufacturer's instructions included with the switch.

switch is only on systems with an optional console that includes a dirty filter light. The pressure switch is set during installation so that the light will be activated at approximately 50% filter blockage. Contacts should close at .17 to 5.0" w.c. ± .05" w.c.

Service: Clean the sensor tubes. If the dirty filter indicator system still does not function properly, check the setting of the switch. With clean filters in place, blower doors closed, and blower in operation, decrease the pressure setting by adjusting the set screw on the switch clockwise until the filter light is energized or screw is bottomed out. At that point, adjust the set screw three full turns counterclockwise or until the screw is top ended.

If it is determined that the switch needs replacing, use an identical switch. When a new switch is installed, it must be manually set; follow the instructions above.

16. Photoelectric Smoke Detector (Option

SA1)
Location: Field-mounted in	Figure 28 - Photoelectric Smoke
	Detector (cover removed), P/N
the discharge ductwork.
Function: The detector will	159553, used with sampling tube,
	P/N 159714
shut down the system if
smoke is detected in the dis-
charge ductwork.
Service: Clean the external
surface. Check the wiring and
connections.
17. Firestat (Option BD5)
Location: Field-mounted on the dis-
charge ductwork so that the sensor		Figure 29 -
extends into the duct. This control
		Firestat,
requires manual reset so should be
		P/N 42782
mounted in an accessible location.
Function: The firestat will shut
down the system if the temperature
in the ductwork reaches 200°F. The
switch must be manually reset.

Service: Clean the external surface. Check the wiring and connections.

18. Freezestat (Option BE2)

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.

Location: The control is in the blower section electrical box; the sensing bulb is field-mounted in the

Figure 30 - Freezestat Controller, P/N 126170

15. Dirty Filter Switch

Location: Switch is located in the main electrical box (See Figure 7); sensor tubes run to either side of the filter rack; indicator light is on the remote console.

Function: The dirty filter switch is a pressure switch that activates an indicator light on the remote console when the filters need cleaned or replaced (See Ser- vice Section, Paragraph 2). This

Figure 27 - Dirty Filter Pressure Switch, P/N 105507

discharge duct.

Function: The freezestat will shut down the system if the discharge temperature falls below the setpoint. The switch is automatic and will startup the heater when the temperature reaches the setpoint.

Service: Clean the external surface. Check the wiring and connections.

REFERENCE: For service and troubleshooting information on the electrical controls, refer to the manufacturer's literature covering that component. Component literature is included in the literature envelope shipped with the system.

Refer to Paragraph 19 for unit troubleshooting.

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