heat not working

So a couple weeks ago I noticed that my Mazda wasn’t blowing hot air from my heater if I wasn’t moving. As soon as I start driving it gets hot but at a stop light or something it blows cold air. I let that go on for about a week while I researched a lot and couldn’t find anything specific. I...

Hey guys, it's my first post so be easy on me. I tried searching the forums but i couldn't find proper instructions. I have basically a stock ms3.. just has a sri and clutch masters clutch... Sometimes when Im driving.. the heat will stop working and it blows out straight cold air.. I looked...