This should be a fairly simple controls issue, but fixing it is driving me crazy. I have a 4 ton 2-stage Daikin heat pump (works great) and an Ecobee Smart (the old version) thermostat. I'm very pleased with the performance of both, but I'm having trouble with the changeover from heating to cooling and vice-versa. The Daikin/McQuay HP uses 4 wires to control the compressor: W1, W2, Y1, Y2. The Ecobee Stat uses 3 wires to control the compressor Y1, Y2, O. Daikin R- Thermostat Power Y1 - Cool Stage 1 Y2 - Cool Stage 2 W1 - Heat Stage 1 W2 - Heat Stage 2 G - Fan On/Off Ecobee: R- Thermostat Power Y1 - Heat/Cool Stage 1 Y2 - Heat/Cool Stage 2 G - Fan On/Off O - Heat Pump Reversing Valve (controls on/off operation of the heat pump), energized in cooling I tried installing a SPDT relay to resolve this issue (I bought this one http://www.automationdirect.com/adc...81_-z-_782_-z-_783_-z-_784_Series)/782-2C-24A), but the relay does not throw when O is energized. I know that my wiring is correct because I can manually force the heat pump from heating mode to cooling mode by pressing the button on the relay. However, it does not throw on its own based on O being energized. Do you guys have any ideas on how to resolve this? Is there a relay with lower resistance typically used for this application? Thanks so much!