I live in an ancient (1967) condo with a two-pipe system. Cold supply in the summer, hot supply in the winter.

There is no electronic changeover or even an automatic cutoff valve. The radiator coil has water at the building-supplied temp at all times unless I close the hand valve.

There is a pipe-mount aquastat with 3 wires (black red blue) that was wired in series with the line voltage. I had given up even trying to factor it into the final solution. Old thermostat was able to sense when desired temp was above/below supply temp and run the fan accordingly. It would be nice to get that functionality back, but for now I’d even settle for electronic fan control.

Thermostat is an ancient Honeywell (T694A) electromechanical affair wired directly to a blower. It seems very simple.

After following several posts here and elsewhere, I am stuck. I have the following new equipment:

  • Ecobee 3Lite

  • White Rodgers 90-113 trans-relay fan center

With everything wired up, manually closing R & G on the 90-113 activates the fan, but the Ecobee won’t activate the fan by itself. Various configurations either had the fan always on or always off. Test screen functions did nothing.

after having no success, I tried adding the following:

  • separate 120VAC to 24VAC plug-in transformer (to supply power independent of the 90-113)

  • separate 120V N.O. relay w/ 24V coil (to activate the known-good relay on the 90-113)

It still doesn’t work. Last startup had the relay rapidly clicking on and off. This was my most recent attempt, which did not work either: (I have some concerns about the way the terminals are jumped on the Ecobee) https://www.reddit.com/r/ecobee/comments/hohg69/making_ecobee_work_with_my_line_in_condo/

Can someone please help? I need a wiring diagram. I tried the PEK too. No dice. Please note that Y and W are not connected to anything on any pieces of equipment currently, except where jumpers were specified on the Ecobee (90-113 Y & W are tie points only)

  • 1
    You think 1967 is ancient for a building? That's so American... I consider my house to be "older" and it was build in the 1890s. (Yes, I'm American, too.)
    – FreeMan
    May 6, 2022 at 11:20
  • Sounds like an old electro-mechanical 'stat is smarter than the new "smart" 'stat. ;-)
    – Ecnerwal
    May 6, 2022 at 11:51
  • Can you please edit to provide pictures or a diagram of how the old setup was connected?
    – Ecnerwal
    May 6, 2022 at 13:30
  • 1
    See if this similar answer to another question helps: diy.stackexchange.com/a/239343/43874 . Your fan control is just a relay and a 24v transfomer, and I suspect you have an incorrect connection somewhere.
    – JPhi1618
    May 6, 2022 at 14:50

1 Answer 1


Here is a diagram of how your fan control should be wired:

Fan control

Note that all three boxes on the right are contained in the fan control. The middle box represents the terminal block on the front of the control.

The wires coming from your transformer might be white and black, or other colors. The colors don't really matter so I have used black for both. One wire goes to C on the terminal block and the other goes to R.

The coil for the relay comes pre-wired to C and G, but since you have been working on this already, you need to verify that the coil wires are going to the right spot.

Note, this diagram has been adopted from this other answer that I wrote for a previous question.

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