I had an old fan-coil system in the unit. It has 3 fan speed controls and heat/cool/standby. I am contacting the management for the exact model and specs but since it is really old, no one seems to know (so far).

Now I am looking for a replacement smart thermostats (at least smarter than existing one) that ideally would connect through WIFI. Besides the low voltage ones (they obviously wouldn't work), several high voltage ones (like Mysa or sinope) seems to only be compatible with 2 wires or 4 wires. I have 6 wires (see below for existing wiring). Do you know any products that would work with this wiring? Any suggestions or recommendations are appreciated. Thanks in advance.

The existing control seems to be Lux PSDFC159. enter image description here Upon opening the back panel, it has 6 wires (3 for fan speeds, 1 load, 1 heat, 1 cool). enter image description hereenter image description hereenter image description here

1 Answer 1


To the best of my knowledge there are no line voltage smart thermostats. I've seen a lot of cheap foreign models advertised as line voltage, but the reviews always say otherwise. I can say, with absolute certainty, that there were no models available in October of 2019 when I converted my mom's unit.

Your best option is to power your thermostat with a 24v step-down transformer and use 24v relays to switch the line voltage on your unit. Most good HVAC technicians should be able to handle the conversion and if not, any electrician could do the conversion.

A word of caution if you decide to do it yourself... Make absolutely sure that the 24v step-down is an isolation transformer and not a single wire.

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