lets start with your furnace, just because your flame is blue does not mean your gas pressure is correct, and always clean your flame sensor nothing worse then an emergangy call for that,and most time a GOOD service tech will find a failing part before you end up with out heat at 3 a.m. now withyour a/c it's a must a dirty a/c runs harder and cost more to run sometimes causing premature failure of an other wise good unit preventive service can save you thousands later. example lack of refrigerant can cause a compressor to fail just as to much can cause it to slug either way you'll be buying a new unit before you need toooo.