Connecting to a thermostat controlled AC

In most cases, the Air Ambient is connected to the indoor unit associated with the AC system. From here we disconnect its temperature sensor (thermistor) and plug-in our Air Ambient cable. For details on this type of installation: Click Here

But sometimes the AC unit is controlled by a thermostat like the above pictures, in this case, the thermostat is the sensor as the below article explains (although models can differ in operation).

How a bimetallic thermostat switches on and off

1. An outer dial enables you to set the temperature at which the thermostat switches on and off.
2. The dial is connected through a circuit to the temperature sensor (a bimetal strip, shown here coloured red and blue), which switches an electrical circuit on and off by bending more or less.
3. The bimetal ("two metal") strip is made of two separate metal strips fastened together: a piece of brass (blue) bolted to a piece of iron (red).
4. Iron expands less than brass as it gets hotter, so the bimetal strip curves inward as the temperature rises.
5. The bimetal strip forms part of an electrical circuit (grey path). When the strip is cool, it's straight, so it acts as a bridge through which electricity can flow. The circuit is on and so is the heating. When the strip is hotter, it bends and breaks the circuit, so no electricity can flow. Now the circuit is off.

Here is the source of the information: Click Here

Please note: The wireless or wired control units for the AC (like the pictures above) are not thermostats and don't have the room temperature sensor inside.

How to connect?

Well for this kind of scenario, we don't use an Air Ambient instead, we use Air Digital as we do not need to mimic any thermistor resistance values. We only need to open/close the circuit (using a relay NC/NO connections) to turn the compressor on or off.

Let's go by an example:

Here is some information on typical thermostat wiring connections: Click Here 

In this example, we have a 2-stage cooling-only AC.

This means we have:

R = 24V supply

C = Common

Y1 = 1st Stage Cooling

Y2 = 2nd Stage Cooling

Now when 24v is applied to Y1 the 1st stage cooling will initiate, when 24V is applied to Y2 the 2nd stage cooling is applied.

Therefore using 2 Air digitals we can control the R (24V) open/close circuit to Y1/Y2.

If we desired a 23deg temperature in the room we can:

1) Set Y1 to come on at 24

2) Set Y2 to come on at 25

3) Set both to go off at 22