Good to hear zadam.
And for what my opinion is worth, the shop that told you the heater core has nothing to do with the A/C system was correct. The only way the heater core can be used to aid in cooling is when the engine is running hot and the heater is turned on. (The additional cooling effect is accomplished by incorporating the extra fluid capacity in the heater core and the heater hoses themselves).
They also proved themselves correct when they determined that the A/C system had too much freon in the system. That can have just as adverse an effect on the systems' cooling capabilities as not having enough freon.
While it sux that it cost you unnecessary $$ in the process because of the first shop, it's good to hear that you found a shop who knew what they were doing and got the VX fixed. Happy summer cruising!