First my AC quit blowing cold air, but I figure it's almost winter, It can wait. Now the heater doesn't get warm at all. I replaced the blower relay under the hood, but nothing. I've read several threads, but don't see anything. I see 4 items in Autozone that could be the 1. Ambient Air Sensor, 2. Heater Core Temp sensor, 3. Elec Auto temp Cont. Sensor can? Where do I start?