Since the pressure is higher in the tank/mag, the vaporization points gets higher so that it stays under a liquid form at ambient temperature. When you release it in and it gets ambient pressure, the vaporization points decreases, so it expands and become gas again. Due to the change of pressure inside the canister (because you remove some mass), it changes the temperature. Simple maths.
PV = nRT
where P = pressure in KPa
V = Volume
n = moles
R = constant (8,31)
T = temperature in Kelvins
You didn't follow your classes in college?
