How can I use an off-peak controller with my 240v air conditioner?
Here's a work-around. 


Use the 110v smart switch to turn a normal phone USB charger on/off.
Get a USB heating pad for &lt; $2, or if handy w/ solder, a 500 ohm usb-powered resistor.
now you can make a small space slightly warm (or not warm) via wifi
wrap the heater around the thermostat temp probe behind the air filter on the AC. You might have to remove the plastic faceplate, but you don't have to heavily mod the AC.
Set AC to 90F, or whatever a max temp in the room should be if wifi conks out.
To cool the room, turn on the wifi socket, which turns on the usb, which heats the thermostat.
To stop cooling the room, turn off outlet/usb, which allows the termostat to reach room temp in about 30 seconds, turning off the AC, since it's cooler than 90F.


Advantages: cheap, simple, electrically isolated from mains, no permement AC mod needed
Disadvantages: slightly rube goldberg, small lag on on/off, short manual setup routine

Of course, you also need a way to get the temp to the smarts that turns the wifi switch on and off, but that's a different question. you can use node-red to setup a simple control loop based on temps and/or state over-rides, for when you're home on the weekend or whatever.

EDIT: based on comment
If the AC has no thermostat, and you're used to plugging it and unplugging it to control it, you can adapt the above using a 5v 15A relay module instead of a heater to switch the A.C. to the AC on and off. You would power the relay with the USB charger that's being wifi controlled, and connect the relay switch terminals to a splice in the line. If you don't want to splice your landlord's cord (understandable), but an outlet ($5) and pigtail ($15) that fits the cord and splice that miniature "extension cable".