This is on my daily driver (90+ miles a day) Winter is coming again in Chicago (yuk) and my heater core decided to take a crap. GREAT!
I am gonna take the "opportunity" to replace the torn up crappy dash with one I have had for that truck, sittin around here for a year now... so that'll be totally out of the way. At that point can I pull the top off the heater box with the heater box still attached to the firewall and NOT blow off the charge of R12? The AC worked so well these last 2 summers, and I havent had to add a drop of Freon I'd like to see if I could leave that alone in the process of replacing the core...

I did a 94 years ago and had to pull the whole box out i just did a blower motor in my 96 that took about 3 hrs you will have to pull the bottom of the dash to get it out ,