Pay careful attention to the floor over the tandems too. If you see blackish lines in the floor, its showing corrosion issues that will be the death of the trailer.
Decker, pride and others used to trade out their equipment at 7-8000 hours. They've now stretched that to 15-17,000 hours. About 1500 hours in a normal year is my usage.
I replaced the input seal on my compressor at 9300 hours and since the system was down, we did reed plates at the same time.
Old company I leased to, did a condenser coil at about 10,500 hours on theirs.
Engine are mainly Kubota diesels in reefers, so should be good to 30,000 hours.
And it all come back to maintenance and how well it was taken care of.