Hi

According to astrophysical theories of the evolution of stars like our Sun, its lowest surface temperature was about 4000 Kelvin (7000 degrees Fahrenheit) which isn't much less than it is now (6000 Kelvin). But the Sun wasn't considered a true star until it got hot enough to burn hydrogen in its core. Before that, it was a "proto-star." A protostar is a large mass that forms by contraction out of the gas of a molecular cloud in interstellar space. The transition from clould fragment to protostar might happen at about 100 Kelvin.The interstellar molecular could might be about 10 Kelvin (-400 degrees Fahrenheit).

There's lots of information in Wikipedia about the evolution of stars if you want to learn more.

Paulett