I currently have a Rheem 10 seer 5 ton mfg'd in 1994. It is not doing its job (3-4 hrs to cool 2 story 2550 ft. house). One a/c mechanic says it's not unit but when its used and a new unit would not make any difference. Another salesman says to buy a 13 or 14 seer 5 ton trane(R-22)with 95% heater and it will make all the difference in the world. Of course the salesman wants $9800 for this switch. I am at a loss.... Is someone trying to put one over on me?