Depends on a few factors that were previously stated. If it was taken care of and did not see a whole lot of use it will last for a long time (relative to what one considers a long time), I had a 1978 Taurus and the AC worked up to the day I got rid of it and it was the original unit (I got rid of that TT this year) so take it for what it's worth. Each unit is different and it all depends on how good it was taken care of and how much use it has seen.
2015 Forest River EVO 2850
2012 Dodge Ram 2500 6.7 Cummins
Yamaha 2k x 2 with parallel cable
EMS 30 PI portable w/ Edison plug
Nights Camped (2016-13) (2015-13)