Hi, I have a 2011 Xterra...winter is officially in full swing and my defrost and heat are not working right. I can crank my truck a good 20 minutes before I need to leave and the windshield will still be frozen! It's blowing cold air, but when I put it in drive and start driving it changes to hot and will defrost fine. I've also noticed my heat can be running fine, then when I am idle for a minute or two it starts blowing cold air, then back to hot when I accelerate. HELP!!