89 Century air conditioning

I have an 89 century and the air is colder on the driver side than on the passenger side and it is a single zone hvac system. don't know when it was recharged last.

An '89?

Is this an R12 system or was it converted to R134a?

Doesn't make sense for this year, because like you say, it's a one zone system, so the air is coming from the same place, for BOTH sides....

Typical low charge scenario, the evap surface is cold on the side that feeds the driver's side, entire evap face should be cold if it has enough refrigerant.