Unless your mechanic or the person you are getting advise from has their HVAC certification - it's all talk. Maybe ask if anyone has their HVAC certification/has experience on here? As stated above this isn't something that's cheap or easily serviceable etc... you can do $$$$$ of damage easily.
Get it done right from a qualified experienced professional.
There's some obvious mis-information contained in this thread, and no problem debating etc.. but let's try not to insult other members.