I have a 2005 Ranger FX4 II. Last week the AC was working great, like new, blowing cold air. Last night I tried to put on the defrost to blow cooler air and it came out piping hot. Now, no matter what temperature I set it to, or what mode (even on AC) it blows hot air. Does my AC need to be charged or is there something else going wrong? The engine is running normally, with no signs of overheating. Any help would be appreciated before I start trying to troubleshoot myself. Thanks.