I have a 2006 xA with about 135K miles. While the air conditioning has never been great, it was acceptable even here in hot-and-dry New Mexico. However, lately, it has been hit or miss. While the air volume is always sufficient, sometimes it's not cool at all. Sometimes it's cool, then not, then cool again during the same trip. Sometimes, it's cool the entire time. I don't know if I'm dealing with some sensor issue or if the compressor is toast. I already had a mechanic look at the refrigerant charge and was told it's fine.

UPDATE: This forum is dead, so I have received no replies. Nevertheless, I wanted to update my post in case someone else faces the same problem. After I posted, a list of related threads appeared, and in one, someone suggested that a poor battery might negatively affect AC performance. My battery was fairly new but small, so I upgraded to one with more cranking amps. This went a long way toward overcoming the problems I was having. Still, the issue (hot air blowing) recurs periodically. When it does, I put the car into neutral and rev the motor to about 6,000 RPM for a few seconds. This fixes the issue, and it usually stays fixed for several days. Maybe my car has a failing expansion valve? (I'm not familiar enough with the AC system to know if high revs would temporarily resolve such an issue.)