Here is the full list of all 13 Swelter achievements.
Tea.
He will not tell wisdom, but he will help find wisdom. Find a yurt with a vortigaunt.
Complete the bonus part.
It is easy to break one straw, but it is more difficult to break a bunch. Bet on unity.
Freedom is life not according to someone else's rules. Bet on independence.
Show your superiority in the air.
Rob the Combine armory.
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.
Get killed by a train run at the very beginning.
Survive a failed train disembarkation.