Wiring – How to wire A/C Thermostat given different wiring conventions

air-conditioningcentral-airthermostatwiring

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 🙂

Best Answer

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.

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