I know this is pretty basic--but my older Rheem Classic IX (in FL) seems to be operating fine--except it stopped heating and I think, cooling. It seems to be running fine, without any obvious leaking. It just blows the same cool air on either setting. Where should I start? Are there fuses to look for on auxiliary heat? Or coolant that needs a recharge? I don't have the manual and I'm a northern boy so this heat pump is a new experience for me.