i have been noticing my rear air con that only puts very little air out, when i put it on heater, its worst,

also when i turn my air con on, sand is pissing out

all this only apply to my rear air outlet,

anyone the casue of my problem?

I think I mentioned somewhere a while ago that the rear vents don't do very much in this car.

As for the sand, I have NO idea!!! Did you car live at the beach and get covered in it?

I'd say first thing to do is tape a vacuum cleaner bag or something like that over both the vents and run them until all the sand is out. It's kind of an elephant in the room when it comes to diagnosing other issues, with any luck it's the only problem but at least you'll have eliminated the sand as a cause once it's all blown out.