Since there was a contractual obligation to get consent before installing an air conditioner, you can argue that failure to do this has substantially interfered with your reasonable enjoyment, lawful right or interest. This would mean serving an N5 notice. The N5 form must provide a termination date of at least 20 days after the notice is given and give detailed reasons for termination, such as specific dates and times of all the events that occurred. The N5 notice informs the tenant that if they correct the problem within 7 days of receiving the notice, the notice will be void and the tenant will not have to move out.

If the tenant fails to correct the situation, then you may file an L2 application with the Landlord and Tenant Board on or after the 8th day. The application must be filed within 30 days of the termination date on the N5. As a side note, when calculating the termination date for the N5, landlords must treat the day that they serve the notice to the tenant as day zero.

The forms and instructions are available here on the Board’s website: https://tribunalsontario.ca/ltb/forms/