how to self diagnose air conditioner issue. blows cold out of one vent?

Many people (on many different cars) seem to say that that AC system only blows a bit of cold out of passenger side when the AC system just has very little power left.

Most likely you are just down on AC gas. You can check that with AC sight glass: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiOpdyf2rzbAhUFliwKHSr4ATcQFggmMAA&url=https%3A%2F%2Fpriuschat.com%2Fattachments%2Fac-air-conditioning-check-sight-glass-pdf.57256%2F&usg=AOvVaw2swGgZRC30llIpytl9Fsk8

Prius uses the special oil in AC system. And the system gets ruined if contaminated with wrong oil. So you need to bring it to a shop that knows what they are doing.

 

Hmm, that's interesting. I'm assuming that you're saying that air blows out of all vents, but only the passenger center vent is cold. If that's the case I'd agree with the prior post. I'd have the system checked for charge, and make sure they know about hybrid systems because there are some critical differences from other systems.

If only the one vent is blowing at all then I'd be inclined to think it's a bad door in the system, but that's a less likely scenario (only one vent has air coming out).