Expert: john t. borgman - 7/9/2009

Question
QUESTION: I HAVE A RUUD 96% FURNACE, I JUST IN STALLED IT AND WHEN THE
SAFTY SWITCH IS PRESSED THE POWER LIGHT COME ON AND THE FUSE
PLOWERS. I HAVE INSTALLED FOUR OF THE SAME KIND WITH NO BROBLE

ANSWER: Cliff,
 You have a low voltage ground somewhere.  First thing to do if your not real good with a volt meter is to unhook all low voltage wires from the board and try one more fuse.  If it blows, then it is a factory miss wiring and you will have to do some searching inside the unit.  If it does not blow then you have a control wire grounded or miss wired.
 Another way is to remove the fuse , tape the safety switch closed and check with your voltmeter with the control wiring removed for something less than 20 volts, like 10 or 15.  Do this quickly, because if there is a problem, you do not want to take out the transformer.
 Next if furnace is ok, remove the tstat and seperate all the wires and the same at the furnace and do a continuity check between all wires looking for a path for electricity.  Same with outdoor unit.
 Of course the first thing to do is double check your wiring, even a seasoned veteran can make a boo boo

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QUESTION: have done as ask, have check control wire it 5 to 8 volts. I removed the transformer and replaced with one from the same kind unit still the same. had some wires to the main plower stuck to gather but no bear wire,check power hookup it was install right. still have same broblem

ANSWER: Cliff,
 You have a low voltage ground somewhere.  Put your meter on ohms scale and with ALL low voltage wires unhooked and not touching from the tsta, and the furnace, including the 2 wires that go to the A/C.  Check between every combination of 2 at a time.........example
 Wires leaving furnace to the tstat...put one probe on red and touch white, then yellow, then green, then blue or whatever you have.  Then go to the next color and do the same thing until you have checked all wires with the one ( probe ) lead from your meter on each color and checking every wire and watch your meter.  You will find that somewhere 2 of those wires have a path for electricity and you will get a reading on your ohm meter reading.
 If by chance still no reading, then put one lead on the sheet metal of the furnace and touch every wire one at a time looking for a reading, this is in case your wires are shorted to the furnace as it passes through the cabinet.
 What wires were melted together?  Did you un-stick them and make sure they are not touching?  
 OR are you saying that with no wires attached to the furnace that you get 8 volts from the board between C and R.  If so the short is in the furnace and you have to look there through all the low voltage wiring.

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QUESTION: I DO NOT HAVE AIR CON. NO WHAT I MEANT WAS THE TOO WIRS FROM THE TRANSFORMER WERE I GOT THE READING OF 5 TO 8 VOLTS, THE WIRES THAT WERE STUCK TOGETHER WERE NOT MELTED TOGATHER AND THIER WAS NO READING ON C AND R. WILL CHECK WIRES AS YOU HAVE ASK


Answer
Cliff,
 Unhook the low voltage wires from the board , That come from the transformer.  If you still have still have the same problem with them unhooked, check your  wire nut connection in the 110 volt junction box on the side in  the furnace where your power comes in and check for a short there or clean power there