If you want to complete all of the story missions in Modern Warfare 3 Zombies, you need to know how pretty much every corner of the mode works. Luckily, for long-time players, a lot of this stuff has carried over to this new iteration. In Act 1, you will have the Freezer Burn mission to slow 50 zombies and 10 hellhounds with the Cryo Freeze Ammo Mod. On the surface, this sounds pretty straightforward, but finding the mod can be a little tough. Here is how to get a Cryo Freeze ammo mod in MW3 Zombies.
Where do you get Cryo Freeze ammo mod in Modern Warfare 3?
Unfortunately, the only way to get the Cryo Freeze ammo mod in MW3 Zombies is to get lucky. Ammo mods are rare to find, so when you find them, they have a blue color to them. The best way to find them is to open Aether Caches. These look like loot chests that have purple crystals stuck in them. Most of the time, these are rewarded for completing things like Infested Strongholds, where you have to clear out cysts. Sometimes, you might just get lucky and find one in a random location. Ammo mods can also appear in Reward Rifts, which appear after completing contracts.
Outside of getting lucky and finding a Cryo Freeze mod to equip, the only way to guarantee you will have this add-on is to get lucky enough to get a Cryo Freeze Ammo Mod Schematic. Unfortunately, the drop rates for schematics are far more rarer than the normal mod, so it is not likely you will come across this. With this, you will be able to craft the ammo mod before you start a MW3 Zombies match to put in your rucksack. This way, when the game starts, you can instantly equip it with the weapon you are holding. After crafting a schematic, it will go into a cooldown before you can use it again.