HVAC PM Issues

[Wally Burbage]

We have 24 units and are constantly getting calls that the drip pan is overflowing and unit is not working. When we send a tech out they usually find dirty coils and a dirty filter if there is one at all. 

I am going to start an annual preventative maintenance program for the HVAC units.

My question is what is the best way to make sure tenants replace filters on a regular bases? Does anyone charge tenants for not changing filters? Do you provide filters? Tks.