Ok, I have absolutely NO clue how the heater in a car works.

But either way, the heater in my car isn't working. Well, barely. When at max heat, it blows slightly warm, and takes forever to get to even that temperature.

What's the culprit? What do I need to go about fixing this?

 

Okay here is your problem. Your heater core needs to be back flushed. Mine was in the same boat as you for 3 years until I back flushed mine. the heater core has two hoses attached to it. One is the inlet, the other is the outlet. Disconnect both hoses and attach a garden hose to the the outlet side which is the bottom tube. The heater core is located just left of the engine against the fire wall if you are looking at the motor from the front. Once the garden hose is attached turn on the water slowly and just watch all the crap come flowing out. Good luck.

 

94blackz14.2, is 100% correct.

But if you want to read more, do a search , there is a ton on this subject.

If backflushing it doesn't work, then the heater core may be bad, there is a lot on that if you do a search.

Most likely it needs to be flushed. Good luck and hurry up, its cold out!!