How do I know if my AC needs recharged?

Why does my AC not blow cold?

So first of all, an oxygen sensor, the old school ones that have been around for a very long time, they change voltages based on the amount of oxygen in the exhaust. So typically below half a volt, the system's lean above half a volt, the system's rich.

Typically it would be because you have an engine misfire and when you have an engine misfire, you can very quickly overheat the catalytic converter.

Now first of all I want to make sure that we're talking about the correct light. There's a light that looks like a little oil can or Genie lamp

The acronym MAP is Manifold Absolute Pressure. Basically one of the things that an engine does is when the Piston comes down, it sucks it and creates a vacuum inside the engine.