So on saturday i was going to work and my heater would not get warm. It was blowing cold air through out the whole day. Then on sunday it worked, and now it doesnt work again. any ideas?
its on 04, 36,500k on it.

I had the same problem with my car. the dealership repaced the a/c unit or something. it was free with warranty.

http://www.rx8club.com/showthread.php?t=158200

^+1.
I had to do this same thing on another guys RX8 a few weeks ago.
Perform the "Easy Diagnosis" in that thread above to see if this applies to you.

okay i'll go ahead and try the easy diagnosis first and if not i'll have to take it in again.

Hopefully it works because my car doesn't have any warranty!

i did the above fix a couple of weeks ago...now it works perfect and i think my a/c feels colder now..it may just be me..it didn't take long at all and it would have been alot faster if me and my friend remembered to hook up the plugs for the temp and the speed control...had to take the console apart 3 times...i think i can do it with my eyes closed now

thats good to hear! I'm hoping mine will feel the same because my A/C doesnt feel that cold either.
Im hoping to get it done this sunday. Ive never done anything like this.