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Using a fluke multi meter how do I find low voltage problem between furnace blower and condenser

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  • cocodulce_74 Apr 04, 2011

    Very helpful..thanks a bunch...



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Go to the low voltage terminal board in your furnace. Follow the thermostat wires ti find it. Set your meter above 30 volt A/C. Hook one lead to one side of the transformer. Touch the other to the RED wire on the terminal strip. If you don't read 24 volts, switch terminals on the transformer and touch the red wire again. If OK then touch your lead to the YELLOW wire or the terminal marked Y on the terminal strip with the thermostat set to cool. you should have 24 volt now between the lead on the transformer and the one on the Y terminal. Go to the condensing unit outside and test the 2 18 gauge wires there. the 2 readings should be the same. If you have any trouble with anything, please write me back.

Posted on Apr 03, 2011

  • cocodulce_74 Apr 03, 2011

    Well after finding a bad 120/24 40va transformer I replaced it and I shud haved fused it but I didn't any ways I hooked up the new one and tryed jsut the fan in the on position and all was ok the fan came on so I put the doors back on when I put the tstat to the cooling there was a small delay when the cooling came on the transformer sparked and smelled burned so I'm fixin to put fused transformer with a built in fuse reset button.sonow I know my problem is between my condenser and my blower what's the easiest way to find the short ground...thanks C.

  • Roger Jelinek Apr 04, 2011

    Sorry I'm late getting back. The fan runs fine so you are probably OK in the furnace. Just be sure the wires from the terminal board in the furnace to the condensing unit are not shorted. With all power off, tie one lead to the furnace cabinet and test all the wires on the terminal board. If any are grounded and its not the transformer common, trace it out. If the "Y" terminal is shorted (Yellow to AC), look at the contactor in the condensing unit. If the contactor LOOKS OK, disconnect the 2 low voltage wires from it and test each separately to the unit cabinet. Test the leads on the contactor last. The contactor is most likely the culprit but its a good idea to test every thing. I'll be back and forth on here for a couple hours. Let me know how its going before tying in the new transformer. Thank you for writing and please grade, OK?



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