Try leaving it on for an hour or so, then feel the back of it, where all that insulation is on the RH side. It's not going to burn you, but you should darn sure feel the heat (with or without ammonia in it). If you feel the heat, and the unit is reasonably level, leave it on overnight, and check the freezer to see if it's cold the next day.
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake