f1

hi guys, I'm using my g/f bro's car for a few weeks and it's got an annoying prob. It's a mk 3 Cavalier and even with the heater setting on cold it still blows warm air through the vents. I know its warm outside but this heat is more like i've got the heater setting to hot ?? It's really stuffy this time of year with the heating on !!! I said i'd try getting it fixed, any ideas what it could be ?? Thermostat maybe ??

Cheers

Stevo