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Service Reference Manual UNIT COMPONENTS
5-21
SRM-HW/HWC 2/99
Pressure Switch (*57)
These are Normally Open switches that react to a difference in pressure
on an internal diaphragm. It will not allow ignition to start if the induced
draft blower cannot produce sufficient negative pressure relative to
atmospheric pressure or pressure in a sealed burner box. Its electrical
contacts will open in reaction to inadequate negative pressure resulting
from excessive venting system restriction or a failed induced draft blower,
thus providing protection from a change in safe, stable furnace operation.
The Armstrong part number is stamped on the body of the switch. A label
on the switch carries the manufacturer’s model number. Always verify the
proper switch number from the parts list.
Connect to Port on
Induced Draft Blower
Electrical Switch
Common Terminal
Normally Open
Terminal
FIGURE 5-18 Pressure Switch
Pressure Switch Specifications
Manufacturer: Tridelta Industries
Electrical Rating:
SPDT Elec. Load: 28 VA Pilot Duty @ 24VAC
3 FLA, 18 LRA @ 24VAC
SPST Elec. Load: 5 A Resistive @ 24VAC
Electrical Switch: Single Pole, Normally Open, Snap
Acting Contacts
Electrical Connectors: Common (C), Normally Open
(NO) 1/4" x .032" thick quick connect terminals
Maximum Pressure: 3" W.C.
Operating Temperature Range: – 40° to 190°F
Sample Line Connector: Negative; barb type for use with
3/16" or 1/4" I.D. tubing with .016" +/– .004" bleed hole