Air conditioner not cooling

[Ana Vhan]

On my rental in the arizona area, I missed renewing the warranty which I was hoping would take care of the AC unit fixes. 

Now, the tenant has reported that the unit is working but its not cooling the place. 

I have asked an AC person to look at it. But I am concerned about the cost. 

A couple of questions, 

1. What AC problems can be caused due to poor handling by tenants? for ex. not changing filter regularly. Any other? Which types of AC costs can I ask the tenant to cover? (we do have a clause in the lease for regular upkeep of AC )

2. Almost all warranty wait period is 30 days. If I purchase the warranty, is there anything I can install temporarily during the wait time? 

Thanks,

Ana