changing heat only tstat to heat and cool tstat

Discussion in 'HVAC Heating & Cooling' started by journeymant, May 3, 2010.

  1. journeymant

    journeymant New Member

    Jun 30, 2008
    forgive my lack of intelligence.for i am an electrician.i have a repeat customer w/ a split system mobile home furnace w/ heat only stat (2 wire) and wants a heat and cool stat "since i was there".the furnace has 2 switches on it,1 for cont or auto,the other for heat or cool.the way it works now (w/ original stat) is only the heat can be converted from cont or auto. flip the heat and cool switch to cool and the a/c works fine but will never shut off regardless of the cont/auto switch. of corse the new stat has 4 (or 5 ) terminals y-g-w and rc-rh jumpered.the handler has 3 ( y-t-tx). T and TX are for the original stat.Y is for 1 condenser wire, the other condens wire is nutted to a wire comming from the heat and cool switch (on the furnace). now ive tried the new stat not touching the furnace wires.removed the jumper between rc-rh, tied red to rc, white to w and still the a/c runs cont even w/ stat off.i do know that W is for heat,Y-cool,G-blower and red.tried numerous configurations inside the furnace. found one that almost worked.condenser kicked on but no blower.could someone please send me a digram of what needs to happen like to keep customers happy.(coleman mobile home furnace,model#7680B,80000 btu)thanx much
  2. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    As you probably know, many things designed for "mobile home" are odd balls. They don't have to comply with the same codes as houses, and for obvious reasons are made with "compact" features. You really need the manual and wiring diagram for the furnace, which you might find under a cover. The furnace may have the option to bypass the internal fan and H/C switches, and externally wire those functions. You have to find out how to wire that. At this point, you apparently have two wires to the furnace. That will NOT control fan and H/C, so you need more wires and you need to know how to wire the furnace. Look for that manual and diagram.
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