HVAC service agreements

[John Kennedy]

I'm looking for advice on how to handle HVAC maintenance for my rental portfolio of 30+ units.  I have signed up for annual service agreements for some of my properties but not all.  I have agreements with a few different companies just based on who happened to install the unit at that particular place. 

At my own house I have never had service agreements - I just change my filters every now and then and have rarely had an issue!  

I cringe every time they call to set up an appointment for the annual furnace check or a/c check because they always seem to find stuff wrong! ($) In my mind I know it's probably the right thing to do to have the routine maintenance, but I sometimes wonder if I couldn't just deal with issues if and when they arise.  In this market it costs around $200/yr for a twice-a-year check up (furnace in fall, ac in spring).

I guess I'm leaning toward putting out requests for quotes for the whole portfolio to see if I can get a quantity discount on the checkups.  Alternately, I may just bag the checkups by HVAC vendors and have my handyman schedule filter changes on a regular basis - then deal with breakdowns when they occur.

Any suggestions? (be kind, haha!)