[DeusIrae]

Actually, that's not true. In general, higher pressure does increase the melting point, but water's different due to the fact that ice takes up more volume than liquid water. For ice, high pressure decreases the melting point, so that it will melt at a lower temperature. Vacuum will, as the adventure apparently says, keep the melting point higher and therefore make it easier to keep in solid form (the effects of pressure on boiling points are different than they are for melting points, which is why your example doesn't work).

Frankly, I don't see how getting the sign wrong on this particular physics question could turn a good module bad or a bad module good (presumably the characters would need to use basically the same kind of widget to pressurize or depressurize the chamber, so whether it's set to suck or blow seems completely irrelevant). So if you think it's bad, it's likely still bad. But this isn't one of the reasons why.