Right you are…I think that settles the matter then. 
Well if it was summer, it would get warm in the car…
punching a hole in an AC condencer would cause a spray of supercooled CO2, like seen in the show, and that would stop a car after a while too.
Puncturing the AC condenser would stop the car? Explain how, please.
Air con is hardly essential to the car’s operation, it’s an comfort accessory that has little to no bearing on the engine running, unless the pump jams somehow and snaps the drive belt which can also drive alternator, power steering pump, injector pump and/or water pump.
Only if it is a Prius or similar hybrid where the AC is used to keep the onboard electronics (and zombies) cool.
No AC = no go on those cars.
[nitpick]No automotive AC system uses CO2. Currently they all use R 134 [/nitpick]
Copper and brass conduct heat somewhat better than aluminum, but the fins of a brass radiator are joined to the tubes with solder, which is a poor to mediocre heat conductor, so creates a bottleneck for the heat flow. Aluminum radiators use aluminum brazing for the purpose which conducts heat better than solder, with the net result being that the Al radiator works a bit better than the brass ones.
My personal experience with two brass replacement radiators is that the are markedly less durable than Al/plastic versions. In one vehicle I own, the OEM Al/plastic radiator went ~120Kmiles, and started seeping where the tanks join the core. I coulda/shoulda had this fixed, but thought a brass radiater would be a better idea. This started leaking after 20K miles or so, but it was brass, so I got out the torch and fixed it…several times, another repair being needed every 5Kmiles or so. It was like whack-a-mole trying to keep up with the leaks. After fixing it perhaps half a dozon times, I gave up and bought a new brass radiator, which performed about the same.
So I decided that plastic/aluminum radiators maybe were not such a bad idea, and found an OEM type replacement. It has been holding water for 50Kmiles now. For those keeping track, I am nearing 300Kmiles on this vehicle. After this experience, I would seek an Al/plastic replacement even if the original were brass.
Part of the problem may have been the soldering on these aftermarket radiators. It had the dull, crystalline look of a “cold” solder joint that I would look for when troubleshooting electronic problems. I certainly don’t recall having so many issues with brass radiators when I was growing up, though Dad did have occasion to teach me how to fix them, so maybe it just seemed normal.
Oh yeah, to the OP: Poking a hole in a radiator is REALLY easy. A knife would make a big enough hole that you wouldn’t get many miles. A little farther than it takes before you start lowering the heater setting on your way to work. Lack of cooling is partly what finally stopped the “kill dozer” in Grandby, CO. You can see the huge clouds of steam after it runs over a lamp-post.
Designers do try to place the radiator back a bit so that it has a chance to survive very minor collisions, so as others have said, you would need a pretty long knife. A big screwdriver might be a better choice of tool if you were setting out to do this.
Nearly invisible pinholes will have you topping off the water every few hundred miles.
pretty much everything I’ve seen in the last decade. Almost universally aluminum cores with glass-reinforced plastic tanks.
radiators don’t physically contact the body of the car; they’re mounted in rubber or plastic isolators for vibration protection.
CO2?
im not sure how much luck./strenght would be required to actually stick a knife into a radiator. but if you did manage to, it would disable the car for sure. i know this from experience. i was in a small crash once and got a crack (way smaller than jax’s knife would have made), and coolant leaked out. i was only about 2 blocks from home so i decided to risk it and drive. the engine overheated almost instantly and i made it about half a block before smoke started pouring out the bonet (and the computer in the engine shut the car off, i presume, because it went dead). it was in fall, and was probably about 15C out. the car was otherwise in reasonable shape and wasnt too old or anything. in my situation the car had obviously been running recently and that was the same in the scene in SoA. perhaps you could make it a bit further if it was from a cold start. but at a significant risk to engine and you wouldnt get further than a min or so walk distance.