Tenant unauthorized alteration, wants reimbursement

[Howard Chang]

Hi, I've come to ask a problem I am facing with in a townhome rental property my parents own. 
In July, the tenant purchased a $8500 new 3 ton AC unit to replace the already working unit (previous was a smaller size that he was unsatisfied with). It wasn't until a month later he had told me about the upgrade. With such a large installation, shouldn't I be notified for authorization this AC company? I know that HOA have to be notified since they had to be up on the apartment roof.

The problem gets more complicated as my parents want to make financial changes thus requiring him and his family to be evicted after the lease is over in December. They've been good to us over the last 10 years and we never raised the rent on them, so we offered $2000 to him for the AC unit. The tenant countered with $2000 + 3 months of forego rent which equals a little under what he paid for for the new AC unit. 

Main point is my parents did not get approval for this purchase on their property. If so, they would have gotten something way more inexpensive and could have avoided this issue. 

Any advice on what our family should do moving forward? Anyone with a similar experience or knowledge is appreciated! Thanks all!

[Ned Carey]

@Howard Chang i am not an attorney and the following is not legal advice. It is simply how I might handle a similar situation.

I believe you owe them nothing and anything you give them is a bonus they have no right to expect. I would definitely give them something. How much to give is a subject of ones own conscience.

They took a big risk by putting money into a property they didn't own. That risk is coming back to bite them.  That was their own choice and a pretty poor choice at that.

I believe our society would be better off if we stopped protecting people from the consequences of their own choices and actions.