Air ride self leveling suspension not working. Compressor works. Height sensor?

We took ours in last spring thinking we needed new shocks. According to the repair shop the air line( under the back seat?) came unhooked. They just had to put the hose back on it. The cost was $45. I've been trying to look up online exactly where the hose attaches because it has come off again and I don't want to have to go back to the repair shop to get it fixed.