Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

need wiring help (homeowner)

Mark, it worked! switching to the E position now gets the fan to kick on an off as the unit calls for heat. This is great, thanks so much for your help. You don't now how happy I am that the system is now working. Now I can schedule some estimates without the time pressure to get my entire system straightened out for the long run.

Thanks again, this forum is great..


  • Geoff_2
    Geoff_2 Member Posts: 5
    problem with fan control

    I have a hotwater hydro-air system in my upstairs and the fan for the air handler will only turn on when I put the fan switch in the on position, the fan will not run if the fan switch is in the auto position. This was working and I think the last guy who was in working on the AC switched some wiring.

    Should both the yellow and green wires go to the same green wire on the air handler?
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Sounds like...

    If the green wire was connected to the yellow wire (assuming the color-coding has remained intact) the fan will operate only when the sysem is calling for cooling. The yellow wire is the cooling wire and the green wire is the indoor fan wire. The green wire should be connected to the "G" terminal on the thermostat.

    Now, there are a number of different control schemes that can be used to control your fan in the heating mode. For example, the fan may be wired to run only when the hot water coil has reached a predetermined temperature to prevent cool air from being circulated throughout the occupied space. You need to check into the specifics of your system as far as how it was initially installed and intended to operate.
  • superMARKet
    superMARKet Member Posts: 87

    Depends on what's at the other end of the white wire.

    (And a few other things, but that's the biggie.)
  • Geoff_2
    Geoff_2 Member Posts: 5

    Thanks for the quick responses.

    So you are saying since both the yellow and green wires from the thermostat are attached to the same green wire on the air handler the autofan will only work with the cooling? That would explain why in the summer the system was working fine.

    How can I get my thermostat to drive the fan in auto mode? I think the problem is that the fan used to kick in based on a sensor in the valve head that controls the flow to the coil. I will try to get someone in to replace the valve if possible. In the meantime can I get my thermostat to drive the fan in automode by somehow tapping into call for heat wire (white). I just need the fan to turn on and off with the call for heat, it doesn't have to be smart enough to switch on based on heat to the coil until I can get someone in to rework the system.
  • superMARKet
    superMARKet Member Posts: 87
    Which thermostat?

    Some thermostats have settings (an E-F switch or a hidden setup item) that will make them turn on the fan when the heat comes on. I wouldn't go changing any connections, since it sounds like you've already got too many things connected to the air handler. (Your thermostat controls cooling, too? Sounds like the air conditioning might come on too when you turn the fan switch to manual on, even in heat mode.)
  • Geoff_2
    Geoff_2 Member Posts: 5

    The thermostat does control AC as well. The thermostat is a programable honeywell unit that has been around for some time. It does have a E/F switch. The switch is in the F position. I will try the E position to see if that helps.

This discussion has been closed.