Your thermostat control inside the air conditioner may be set too low. In a Dometic Brisk Air, the thermostat has a tiny screw close to the rheostat to adjust to the temp you want it to stop cooling at. You have to take the air conditioner parts inside completely apart to get to it. Take the inside panel off, thermostat housing off, lid off the housing to get to the temp control. There are tiny letters and an arrow above the screw pointing to the direction that makes it run and cool longer. I drilled a 1/4" hole in the lid holding the thermostat in, right over where the screw is, then drilled another hole thru the plastic control knob, so now I can stick a tiny screwdriver thru the two holes and make the adjustment without taking it all apart. My conditioner would run for about 2 minutes then stop cooling, then start, then stop. It was set way too high of a temp so wouldn't keep cooling. Then my motor starter capacitor shorted out, but a new one fixed it.