I spend about 2 hr trying to disconnect those "fast connectors" and finally cut them off.
Than since the system has no valve and keeps the heater core under the dash hot even with 120F outside, I added hoses to the heater core and make new junction with 2 valves in easy accessible place under the hood. Next time I have a problem with heater core, I can just shut it off and than at convenient time have conveniently accessible connectors to deal with.
Did I mention that turning off the heater core makes the cabin colder while on 120F desert?
Bottom line -cut off aluminum pipes to the core under your dash, pull the ends under the hood and deal with it where you can see what you are doing.
I went through this about 3 years ago, what a true PIA.
The replacement hoses (from Gates) DO NOT have the core end fittings (THANK GOD)
I first thought I'd gotten the wrong hoses but my parts jobber double checked and found that the ones with the special fittings were only used on the assembly line to save time, the new Gates hoses just slide onto the core fittings and then use a band clamp on them-I saved my old hoses (all of them) for spares-I just cut the heater hoses off right at the stupid factory fittings at the core end.