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Adding a C wire to a very old HVAC

Discussion in 'Social' started by Prasanta, Oct 8, 2018.

  1. Prasanta

    Prasanta Guest

    I have a fairly old HVAC and thermostat in my house and want to replace the thermostat with a new WiFi enabled one. I opened up my thermostat and found there are only 4 wires. (See images below). A peek into my heater reveals no circuit board but a collection of wires. I have a transformer mounted outside and there are two white and red wires that goes in (see pic). The 4 wire cable that runs from the heater to the thermostat has four wires red, white, green and blue. The blue one is connected with the white wire coming from the transformer and at the thermostat end, connects to a yellow wire coming from somewhere else.

    Does this mean I have a C wire? I am assuming the blue wire that is connected to the transformer and can supply me the necessary drive. Where is the Yellow wire coming from and why was it connected to the blue one at the thermostat end? What changes do I need to do for connecting a smart thermostat?


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