Modine Manufacturing HD Manual page 151

Three Flashes – Open in the Safety Switch Circuit
When there is a THREE flash troubleshooting code, the unit is indicating that the limit
switch or flame roll out switch is open.
• The limit switch is ignored unless a call for heat is present (R to W energized).
• If the limit switch is open and a call for heat is present, then:
– The control de-energizes the gas valve, runs the blower motor and runs
the power exhauster.
– The control will flash three times on the LED unit the limit switch closes.
– When the switch re-closes or the call for heat is lost, the control runs
the power exhauster through post-purge and runs the blower through
the fan off delay.
– The control will return to normal operation after the blower off
delay is completed.
Possible Causes:
• Open or short in safety circuit (flame roll out switches some and some limit
switches are manual reset):
– Check for open contacts on switches in safety circuit. Reset flame roll
out switches and manual reset limit switches.
– Check wiring for loose connections.
– Replace defective limits if they will not reset automatically or manually
after the unit heater has cooled.
– Defective board, not letting 24 VAC through limits.
ƒ For more information on fixing or replacing a defective board,
reference page 23.
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