Here is the full list of all 13 Swelter achievements.
Tea.
Rob the Combine armory.
He will not tell wisdom, but he will help find wisdom. Find a yurt with a vortigaunt.
Get killed by a train run at the very beginning.
Complete the bonus part.
Freedom is life not according to someone else's rules. Bet on independence.
It is easy to break one straw, but it is more difficult to break a bunch. Bet on unity.
Show your superiority in the air.
Find the AK left many years ago.
The attacking helicopter looks best on the ground. Bring it down.
Open all caches marked with a radio beacon.
Eliminate the missile turret.
Survive a failed train disembarkation.