Wiring help with thermostat and condensor

Discussion in 'HVAC Heating & Cooling' started by Scott Baz, Jul 24, 2019.

  1. Scott Baz

    Scott Baz New Member

    Joined:
    Jul 24, 2019
    Location:
    Boston
    I removed old thermostat and only had a 2/22 wire red/white
    (I have ran a new 5/22 wire)
    Looked at furnace wiring and have 2 black wires from Fan limit switch (one on 24vac transformer other on gas valve terminal)
    White wire to thermostat on other gas valve lug, then red wire from thermostat to other terminal of 24vac transformer
    I don't see any fan contact wires.
    So my question is how do I wire in the new AC condenser and also be able to turn the fan on and off if wanted?

    Thank You In Advance
    SBAZ
     
  2. Stuff

    Stuff Well-Known Member

    Joined:
    Mar 7, 2013
    Location:
    Pennsylvania
    With a fan/limit switch the fan has its 120v feed switched. Lots of those old furnaces required an a/c kit to enable fan control. This basically added a relay for the fan in parallel to the fan/limit switch.
     
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  4. Stuff

    Stuff Well-Known Member

    Joined:
    Mar 7, 2013
    Location:
    Pennsylvania
    Picture didn't come through. Do you have a make/model number of the furnace?
     
  5. DonL

    DonL Jack of all trades Master of one

    Joined:
    Mar 30, 2011
    Occupation:
    Rocket Scientist
    Location:
    Houston, TX
    Not really. Do you have a schematic ? That will show what needs to be done. Will also avoid smoking something.

    upload_2019-7-25_9-34-38.png




     
    Last edited by a moderator: Jan 13, 2021
  6. Stuff

    Stuff Well-Known Member

    Joined:
    Mar 7, 2013
    Location:
    Pennsylvania
    Something missing here. If there is a condenser then a pro should have been there to install and should be able to wire this. DonL's pic shows old system. Trace from fan/limit switch back to blower to see if there is a relay there.
     
  7. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Please clear this up. You had a heating forced air furnace and you just had a central air system installed, The A coil was installed above the plenum on this furnace. How did the tech test the AC? Was it agreed that you do the wiring?
     
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