Harassment from neighbour with his noisy split ac compressor

Send a legal notice through a lawyer to both the parties i.e. the owner and the tenant, specify your problem and ask it to be resolved within a stipulated time. Also keep the acknowledgement copy received from the post or courier after the delivery of such legal notice. Be specific on the point that if the problem is not addressed and resolved immediately strict legal actions will be taken against them.

Thanks and regards,
Adv. Sagar Verma
advsagarverma.official@gmail.com

Try to solve the issue by amicable manner. if not cooperate then find legal remedy by notice and complaint

Hello, Greetings of the day!
For the query you posted, I would suggest that:
First, try to settle amicably but if in case matters are in the stage where legal action is needed; 
Then, send a legal notice with the help of a lawyer and specify your concern, and request that it should be settled within a stipulated time. Likewise, keep the acknowledgement receipt which you will get from the post or dispatch after the conveyance of such legal notice. Be explicit on the point that if the issue isn't addressed and settled promptly strict legitimate action will be made against them.
Also, you have an option to go for the Alternate Dispute Resolution like Mediation where parties in dispute discuss their concern with the assistance of a trained impartial third person who helps them in reaching a settlement.
Hope it helps
Regards,
Sneha Jaiswal
 

Thank you so much for kind reply and you valuable suggestions. We have been trying to convey the problem from more than a year now and neighbour is completely insensitive. Talking owner is also taking very long time. I see only legal way is left for me to resolve this issue.