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  1. #1
    Join Date
    Apr 2002
    Western piedmont of Carolinas
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    dual transformers. How to rewire?

    Working on old moble home electric furnace w/add on a/c. H.O. called with complaint of no heat. After find the wireing messed up, he admitted to replacing the t-stat. Found the rc/rh jumpered as is typical, but then noticed two red wires tied together at a/h. Further investigation found seperate transformers in A/H and cond. unit. H.O. swears he only touched wires @ t-stat, anyway I managed to get the heat going, but fried the OD trans. I've heard of seperate trans. , but this is the first I've seen. No diagram available. What's the best way to fix this? Why not rewire w/one trans., or does the seperate one for heat have something to do w/the fan interlock or something unique to this system?

    Thanks for the help.

  2. #2
    Join Date
    Oct 2003
    Florida's space coast
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    Just remove the Rc-Rh jumper and you have two separate circuits.
    We've been doing so much,for so long,with so little, that now we can do almost anything, with nothing at all.

  3. #3
    Join Date
    Aug 2003
    Fort Worth, TX
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    Key word here in your post is "old" mobile home. Dual transformer split systems are rare these days...hard enough to get many installers and techs out there to understand wiring a single volt transformer system correctly...imagine throwing another transformer in there as a matter of routine!

    IMO, the dual transformer systems were a product of when furnaces were sold by themselves, with a/c as an option. The VA rating of the furnace transformer was not enough for both furnace and outdoor sections, so a separate transformer came with the outdoor section should the buyer choose to have both heat and air installed in his mobile home. That's just my take on it...might be a better reason for it than that.

    Was it you or the homeowner that fried the outdoor transformer?

  4. #4
    Join Date
    Mar 2007
    NW AR
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    I rewire these cobbled up messes all the time.

    Two transformers, two-wire t-stats with reversing switch, the auto/fan switch. Its all junk. If its been worked on a couple hundred times(indicated by hundreds of wirenuts) Ipull the whole rats nest out and start from scratch.

    One transformer, 4-wire to the stat, new stat, and I completely do away with the fan toggle switch on the a/h.

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