the burning fuse

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  #1  
Old 12-04-08, 03:31 PM
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Cool the burning fuse

please help! I have a Ducane furnace model FPBB075A3 upon trying furnace this year unit would do nothing . after trouble shooting replaced burned transformer
on primary side.(115v--24v) and blowen fuse on circuit board.
5amp .. each time with power on to unit, fuse keeps blowing,
even with thermostat wiring and blower harness disconnected.
what could keep blowing fuse???william55
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Old 12-04-08, 05:30 PM
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I wonder if you have a 24v x 120v relay that is shorted inside, so that the 24 volt side of the relay is not only closing or passing current through a resistor coil, but somehow something got bridged inside, and 120 volts is getting into the 24 volts. That could possibly explain how both a fuse and the transformer might have blown.
 
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Old 12-05-08, 08:43 AM
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Thank's for the reply ecman51 Voltage reading on primary is 122v secondary 28v do you think 4v would make the 5amp fuse blow?
 
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