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24v HVAC control (US) - FAN (Green) always engaged when call for heat, is that normal?

wvriem
wvriem Member Posts: 34
edited February 12 in Radiant Heating

Hi,

I have a question about the correct way to control the fan in an air handler.

I have a First Co air handler with hydronic heat from an oil boiler, and a single stage compressor/outdoor unit for cooling.

The air handler is documented to delay the fan (for approximately one minute) on a call for heat (so from the moment the thermostat switches 24v on to the W wire), so the hydronic parts can warm up before the fan starts - otherwise it'd be blowing cold air around, very uncomfortable.

The thermostat is connected to the air handler, oil boiler and compressor using 24v signals on W (heat), Y (cooling), and G (Fan). So 24v from R (power) is connected to the desired function (W,G,Y) by the thermostat. Seems to be exactly as it says in the installation manuals. Everything works - heating, cooling, fan. That's not the problem.

Problem is that the thermostat also always switches on the G (for fan) too when calling for heat. Obviously, this starts the fan without delay and causes the uncomfortable situation that it's blowing cold (or cool, but definitely unheated) air around in the room. Very uncomfortable.

If I disconnect the G (fan) from the air handler then it would delay the fan as expected, but then I no longer have the option to use the fan separately. Not how I expect it's supposed to be.

I've tried several Honeywell thermostats and they all switch the fan on immediately on a call for heat (and, afaik cooling too). They all have the option FAN ON or FAN AUTO only. No FAN MANUAL.

Questions:

Do all thermostats always engage FAN (green wire) together with a call for heat (white wire)? If so, how does anybody manages the delay for the fan so not to blow cold air at first?

I've read suggestions to put a relay in between the fan wire to disconnect G that when there's a call for heat on W, but that feels like a weird hack to do.

Any body any clues?

Thanks!


Waldo

Comments

  • ratio
    ratio Member Posts: 3,886

    It sounds like your thermostat is set up for not-a-gas-furnace (however it's designated in the setup), which is typically an air handler with an attached heat pump or electric heat strips (or both). Both of those heat sources require the thermostat to turn on the fan. Set it to 'gas furnace' (or whatever) to allow the air handler to turn on the fan in heat mode by itself. (The thermostat always turns on the fan during a cooling call.)

    wvriemmattmia2
  • Big Ed_4
    Big Ed_4 Member Posts: 3,112
    edited February 12

    As mentioned it is how the thermostat is programed .. I prefer to add a aquastat to the return pipe to turn on the fan when the coil is hot enough heat and will shut it off when cooled down ..

    There was an error rendering this rich post.

    wvriem
  • wvriem
    wvriem Member Posts: 34

    Thanks m/ratio, for the hint where to look! Manual doesn't mention anything about this, one of those 'you just need to know' kind of manuals…

  • ratio
    ratio Member Posts: 3,886

    Yeah, it beats me why it's so often called 'gas/electric' or whatnot, when it is only accidentally related to that. Why not just call it 'G on with W' or 'fan on with heat', which it what it actually does.

  • mattmia2
    mattmia2 Member Posts: 11,610

    If it isn't in the manual you have for the thermostat then you need to find the installation manual for that thermostat which will have all the settings and how to change them(sometimes it is in a menu, sometimes it is a jumper).

  • HVACNUT
    HVACNUT Member Posts: 6,558

    Make sure that's not the way it's been wired on purpose. With the thermostat switched to "gas" or "equipment controls fan in heat mode", it's possible there will be no fan at all. W must go to a time delay relay or a sequencer to energize the fan it heat mode. And it's usually a different speed. As of now, it seems W only goes to an isolation heat relay to close TT at the boiler. Are the sequencers there? Are they wired?

  • mattmia2
    mattmia2 Member Posts: 11,610
    https://forum.heatinghelp.com/discussion/comment/1842294#Comment_1842294

    I think they said it worked as expected if they disconnected green.

    HVACNUT

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