Do you mean thermostat?
And do you mean straight cool unit or a heat/cool unit?
if it is 2 stages cooling how many heating?
you can get away with a 5 wire for 2 stages cooling and one stage heating with no common to the stat. Unless you have both stages under the same terminal.
I have just purchased a home. the furnace is about 6 years old with no a/c. I have a friend that works for Johnson Controls and get me a steal on a luxaire 5T a/c unit. i will be doing the majority of the bull work, then brining in an hvac contractor who lives up the road to do the plumbing for the unit. I'm just trying my best to get prepared for him so he can come in, do his stuff with as few hassles as possible.