Is lease clause legal? Tenant questioning it.

[VAL A.]

I own homes in another state.   I've leased them out for a number of years and always had the lessee responsible for full maintenance of the property as if they were the homeowner.   The exception to that is I've paid if the repair was what I considered "major"...ie broken water line underground, roof problems of any sort.   Lease reads:  Lessee will, at its sole expense, keep and maintain the Premises and appurtenances in good condition and repair during the term of this agreement.    

Current Tenant is stating that this clause is illegal in the state of New Mexico.   I have always charged less than market rent to tenants which I felt was a fair balance.   Tenant contacted me in early May re a/c issue--stopped.   I sent a/c co out...thorough check of system--$150 charge to me--unit frozen as apparently tenant keeping unit on and set at 68.     Tenant contacted me again late May--I sent out a/c co again--same issue--a/c co advises customer AGAIN can't run the unit like they are doing---tenant says he can set it at whatever temp he wants!     Now tenant again contacted me...a/c has stopped.   I referred him to his lease.  I had paid the prior $300 "in good faith".    

I feel my lease is completely legal---  Comments or thoughts or references to help please?