Does anyone know of a 240v switch or other means to control an old 240 volt Air conditioner?
Are you in the US?
If you just want on/off, see the following thread:
Aeotech has a 220v Zwave switch rated at 30-40A.
I am using this for my 4500W water heater tank. I run it on 240V with ground, no neutral. L1, L2, GND.
That is a single pole relay. So it all depends on the location of the OP - he hasn’t yet specified where he is.
In the UK, 220V is provided as a single phase, single line (L1 + N) source. In the US, 240V is provided as a single phase, dual line plus, optionally, a null. (L1 + L2[ + N]). Null is not normally required in 240V operation. I base my assumption on the fact that the OP mentioned 240V, not 220V.
Now, about that device, while it can accept up to 277V, it is a single pole relay, which means it will only interrupt one of the two lines, while the second lines will always be HOT at the A/C. Plus, it can only take 10A, so the OP needs to make sure he’s within the limit. It looks more like a device designed to complement a wall switch.
Thanks everyone! Great suggestions here. I will start with the Aeotech solution.