Landlord not returning deposit for AC compressor not working

[Shawn Gor]

My Friend living in Massachusetts. He recently completed his lease. He kept and returned house cleaner than he received from landlord. While moving out walk-through he updated landlord and suggested to service Air Conditioning unit since compressor was not working. Landlord now denying to return deposit money and asking to fix air compressor.  Is it renter's responsibility to fix? What should he do?