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ii. If 24 VAC is present, the probable cause is a failed interface board.
24 VAC is present on interface board J3 pin 9 (LED 5 (GV))
and, on dual units, on J1 pin 9 (LED 1
(GV)).
1. If 24 VAC is not present across the gas valve main coil (MV terminals), probable causes are an open
high-limit thermostat or a failed wire between the interface board and gas valve.
Be sure to check both
valves on dual units.
a. Check continuity of high-limit thermostat and drain safety switch. If both are zero, problem is in
wiring.
2. If 24 VAC is present across the gas valve main coil (MV terminals), the 24 VAC circuit is working
and the problem may be with the gas valve.
Be sure to check both valves on dual vat units.
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