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I've just moved to a new apartment in which I'd like to replace the current central A/C thermostat with a new one with WIFI control. I hope it's possible! I have basic diy electric skills but no knowledge in Air conditioners.

Current Thermostat

The current thermostat has only two switches (beside the temperature knob) :

  1. Cool / Off / Heat
  2. Low / Med / High fan speed

The current thermostat

The wiring of my current thermostat is as follows :

L1-~ L2-0 COMP R.V LOW MED HIGH

If I understand it correctly, the LOW, MED, HIGH are for fan control,

the L1-~, L2-0 are for line and neutral

andR.V, COMP are for 24V from the unit and for the compressor.

There's another loose wire connected to nothing.

New Thermostat

In the product I wish to buy, there's a different wiring diagram, in which the I don't understand which wire goes where. 7 Live Wire 6 Valve OFF - for three-wire electric valve and fan coil 5 Valve ON - for two-wire electric valve and fan coil 4 Low 3 Medium 2 High 1 Neutral

Matching Between the Thermostats

I've figured out the Low Med High should be the same, however I'm not sure about the L and N wires and I definitely have no clue what is the Valve ON/OFF terminals are. So far this is my match between the two diagrams

Old New L1-~ -> Live Wire L2-0 -> Neutral COMP -> ????? R.V -> ????? LOW -> Low MED -> Med HIGH -> High

Here are the diagrams from the product's documentation: The new product's wiring schemes

Finally, the questions :

  1. Are these thermostats compatible?
  2. How to wire the new one to my A/C?
  3. What are the Valve wires?

If there's a solution, a diagram would be much appreciated! If I'm just a noob with no clue and this is not possible, please be gentle :)

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It does not seem that the thermostats are compatible, no. Your existing thermostat is designed to control a heat pump with a multispeed air handler:

  • L1/L2 are likely 24VAC in
  • COMP controls the heat pump compressor
  • R.V. controls the heat pump reversing valve
  • HIGH/MED/LOW control fan speeds
  • the unused wire is just that -- it looks like someone wired your 'stat with network cable BTW, which is a bit of a no-no.

The new thermostat you have is designed to control multispeed air handlers in zoned hot water (hydronic) systems instead -- instead of controlling a compressor and a two position reversing valve, they are designed to control a variable-position hydronic zone valve, typically for heating only as they have no heat/cool changeover system or extra outputs for controlling cooling components.

  • Thank you for making this much clearer! Would you recommend any thermostat that would fit onto my current system? The whole reason I've started looking for this is since my current 'stat does not even have a remote control, nor any programs/timers/etc... so I thought better upgrading it to WIFI to control it from everywhere in my home, but anything better would be appreciated. Regarding the network cable, I would not be surprised if a sloppy job was carried out by the technician who installed it in the first place (that's pretty common in here) – mati.o Jul 9 '16 at 19:49
  • If you can sacrifice the multi-speed fan control, you can use just about any 'stat. If you don't -- you're probably going to have a tough time with this. – ThreePhaseEel Jul 9 '16 at 23:51

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