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Thermostat wiring help please!!

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trivetman
trivetman Member Posts: 179
edited July 2023 in Thermostats and Controls
The local utility gave my dad some ‘upgraded’ thermostat, and was nice enough to send someone over to wire it wrongly!!  I come over at night and the tech is gone and the AC isn’t working.

his thermostat wires are old and without much color.  He also didn’t take a picture of how the old thermostat was wired.   I can tell that there is a jumper on the old thermostat between R and Rc but I can’t tell you anything else about how it was wired before 

i found the box in the basement where the wires in the pic are spliced into modern wiring.
The system is A/C and a furnace.

Looking at the pics below, I find the following:
Rc leads into red.
O/B leads into white
G leads to blue
W/E leads to green

So I switch things such that:
Rc leads to red (no change)
O/B leads to blue
G leads to green
W/E leads to white

hooray now the AC is working!!!

but then I start reading that the O\B switch is for a switching call on a heat pump, which isn’t part of this system.  Is this thing still wired wrong?  If so,  how is it that the AC seems to be working?





Comments

  • HVACNUT
    HVACNUT Member Posts: 5,863
    edited July 2023
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    Can you show the wiring in the furnace? 
    If it's not a heat pump then most likely O/B isn't used.
    Does the thermostat take batteries?
    If it's a so called smart thermostat and desires (needs) constant 24v, then you can wire the Blue to C at the thermostat and furnace.
    Electricity is colorblind so no matter the color, the correct wire needs to land on the correct terminal. As you found, there's sometimes splices in the circuit and what was once Red, is now Blue.
    Your very basic HVAC wiring is 
    R- 24v power
    C- Common (ground)
    W- heat
    Y- AC circuit 
    G- fan
    O/B- reversing valve or actuator depending on the application. 
  • trivetman
    trivetman Member Posts: 179
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    @HVACNUT

    thanks.  Sure enough the ac was on all night and overshot the target.

    heres the termination point.

    there is battery power in the thermostat (and was in the prior thermostat as well)

    i am guessing the blue wire should lead to the Y contact at the thermostat but Ill wait to hear before I do anything.

    Do I also need to put a jumper between Rc and Rh as was in the old thermostat?


  • HVACNUT
    HVACNUT Member Posts: 5,863
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    trivetman said:
    @HVACNUT

    thanks.  Sure enough the ac was on all night and overshot the target.

    heres the termination point.

    there is battery power in the thermostat (and was in the prior thermostat as well)

    i am guessing the blue wire should lead to the Y contact at the thermostat but Ill wait to hear before I do anything.

    Do I also need to put a jumper between Rc and Rh as was in the old thermostat?


    Yes it looks like Blue is Y1.
    Not sure about the jumper. You need to read the install  manual. Some need it, some don't. What make and model thermostat?
    What type of Humidifier, bypass?
  • mattmia2
    mattmia2 Member Posts: 9,741
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    I have never seen a system with that many wires that is old enough to have rubber wires.

    If there is conduit all the way up to the t-stat you could pull a new piece of cable and power it off the transformer instead of using batteries.
  • trivetman
    trivetman Member Posts: 179
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    Thanks guys.  The parents had an hvac tech show up and undo what the first tech did.  Once he showed up I stayed out of it!
  • unclejohn
    unclejohn Member Posts: 1,833
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    Looks like a Lennox furnace and you will need the jumper