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  1. #1
    Join Date
    Apr 2002
    Location
    Western piedmont of Carolinas
    Posts
    1,452

    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
    Location
    Florida's space coast
    Posts
    2,537
    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
    Location
    Fort Worth, TX
    Posts
    11,086
    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
    Location
    NW AR
    Posts
    2,475
    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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