Same thing happened on my 99. It could be the temp valve actuator (Blend door Actuator). When you turn your knob from cool to warm can you hear any door or flap opening or closing under your dash centered right above your tranny hump. Mine was stuck on the heat side and I went 2 years with no A/C due to thinking I was going to have some expensive fix. After figuring out that it was the blend door I ordered one from Rock Auto and had it installed in less then 10 minutes. Could be a possibility... Hope it helps!