Armstrong World Industries 183, 243, 302, 242, 122 Checking Pressure Switch Operation, Blocked Flue

UNIT COMPONENTS Magic-Pak: HW/HWC

5-24

Blocked Flue

Blocked flue is any condition that blocks or restricts the flue (vent) pipe to a point where the pressure fall reaches the calibrated open setting of the pressure switch.

Potential Causes:

•Rodents

•Spiders

•Nest building in the flue pipe

•Outlet screens with excessive restriction

•High wind conditions exceeding 40 mph

Symptoms:

•Low negative pressure on the induced draft (combustion) blower. The unit cycles on and off quite frequently, typically coming back on within 60 seconds.

•Inability of unit to stay on for a complete call for heat.

Units cycling on pressure switch re-ignite sooner than a main limit switch can reset.

Tip: With all wiring connected and unit running, use your volt meter across the pressure switch terminals. No voltage reading = switch closed. Voltage present = switch open.

Checking Pressure Switch Operation

It is easy to check a pressure switch as it operates within the overall system. These test procedures make it possible to pinpoint the opening and closing actions of the pressure switch.

WARNING

DO NOT try to repair a pressure switch. Use an identical replacement. The use of an improperly repaired or malfunctioning pressure switch could result in property damage, personal injury or death.

WARNING

Never try to adjust a pressure switch or jumper the switch to allow the furnace to operate. Doing so could allow the furnace to operate under hazardous conditions, potentially causing property damage, personal injury or death.

SRM-HW/HWC

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