To be only a little more specific, a body radiates heat, and the amount of heat it radiates is an increasing function of its temperature. So the spacecraft is simultaneously heated (solar radiation, internal sources of heat) and cooled (radiation of heat out into space). If the amount of heating is greater than the amount of cooling, the spacecraft temperature will increase, which increases the rate at which it radiates energy into space. If the amount of cooling is greater than the amount of heating, the spacecraft temperature will decrease, which decreases the rate at which it radiates energy into space. Either way, eventually, an equilibrium will be reached (assuming constant conditions, that is, constant exposure to the sun, constant amount of heat generated from the inside, and the like) in which the spacecraft radiates out to space an amount of heat exactly equal to the amount it receives through solar radiation and from internal sources.

So the interesting question is not how the spacecraft was cooled - that's through radiation. The interesting question is what the equilibrium temperature of the spacecraft would be. This of course depends on its design (what is its shape, how much power do the electronics consume, things like that), so it's a little tough to determine that without using specific information about the Apollo crafts.