Yesterday the AC portion of our mobil home stopped cooling. Everything is running, but the system blows hot air. It's a Coleman split unit about 12 years old. Did I loose my coolant? What do I look at first?

If the outside fan is running then the unit is getting power but the compressor inside in not working. There are many different parts that can cause cooling failure. Unless you have knowledge on how to test various parts on the unit it would be best to call for ON Site Service and have the unit checked by a professional.

Hvac, wondering if it's similar to the ac unit inside a car. Last night, my buddy's mustang's ac kept blowing hot air...

Anything is possible especially in a car.

Sneeze, normally in this situation in auto, there is a vacuum leak