I bypassed my rear heater core on the firewall by not using tees when I replaced hoses and fittings. I would have bypassed the AC also, but mine is not the type with the shut off valves. Wudda been easy if I could have just shut the lines off....If it ever leaks, I will cut the lines and have them Al welded shut..........needless to say...I am not concerned with rear passengers...ha