I am in the process of purchasing a home built in 2007. It has a Trane XR13 AC unit that says the min/max fuse size is 50 amps. My inspector told me that I need to use #6 wiring. I spoke with an electrician and he told me that I should downgrade the breaker to a 40 amp and use #8 wiring. Any suggestions? Should I go with the #6 or use a 40 amp breaker and #8 wiring? Thanks for the help in advance.

Look at the metal plate on the A/C unit. It will tell you what you need to know.

It sounds like this unit is currently installed, what is the AWG of the wire connected to the unit? Is this straight AC or a Heat pump?

Before any advice is given we need to know exactly what the nameplate on the unit states.

It will state max fuse size and minimum circuit size.