American Dryer Corp. Phase 5 Microprocessor AD-170 - Manual (Page 15)

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L. Sail Switch (Gas Models ONLY)
The sail switch is located on the front of the burner
box. A sail switch consists of a round damper plate on
a lever arm which is in contact with an electric switch.
When the air blower comes on, it draws air through the
gas burner. This creates a negative pressure inside the
burner box, and this negative pressure pulls in the round
damper and activates the sail switch. If there is
improper airflow, the damper will not pull in,
preventing the burner from starting.
Improper airflow can be caused by improperly designed
exhaust ducting where the duct run is too long or has
too many sharp bends in it. It can also be caused by a
lack of make-up air.
K. Main Door Switch
The main door switch is located in the main door hinge
block. When the main door opens, the switch will also
open, preventing the dryer from operating. The main door
switch is a safety device and should never be disabled.
M. Hi-Limit (Gas Models Only)
A hi-limit thermostat is located at the burner. This is an
automatic reset disc-type thermostat set at 330º F for gas
dryers. If the flame in the burner should get too hot, this
thermostat will shut off the burner. This is generally
caused by low airflow in the dryer.