Stop in for a cup of coffee

Assuming yours is not too much different than an A body, it's not that bad of a job to rebuild the whole heater box with a kit from DMT. Why do you think its the evap?Did he actually check it? That's the most protected part of the system. It's more likely a fitting, or the condenser. I just had my valve cover off. Have to lift the AC line pretty far to get it out. Praying it didn't open anything up moving those lines after I finally got it charged and working.
There was a hissing sound from under the dash last year when he charged the system, and the freon leaked out. This time I noticed a slight unusual odor inside the car. The evaporator/heater core is inside this weird plastic clam shell that is mounted into the firewall with sealant. Don't know if it really is the evaporator, or a fitting, or something else.