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UNIT COMPONENTS Magic-Pak: HW/HWC
SRM-HW/HWC 2/99
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.
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.
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