The posterior of my sisters a/c is vent within the garage. how big a problem is this??
Answers: Garage can get pretty heat. You may wish to consider departing the overhead garage door open when the AC is running to tolerate the heat dissipate to outside.
Shouldn't be a problem. The A/C part recirculates air within your sister's room. It's cooled as it goes through the A/C component, and the heat generate by the A/C unit is one blown into the garage. So, the two atmospheres - your sister's room, and the garage - are kept separate. There is a potential problem however. If she were ever to flip the control switch from "recirculate" to "fresh", the A/C part would draw in nouns from outside, into the room. If there be a car running surrounded by the garage, it would draw in the exhaust fumes.