The sound of the lock panel closing does not prove the lid closed: a box edge caught in the frame, a displaced gasket and a latch that has not fully seated all make the same sound. A few millimetres between lid and body look shut from two metres away, and when the loading-area light comes from the side, the shadow closes the gap completely.
- After closing, read the latch or position indicator described in the model manual.
- If the manual allows it, press the middle of the lid by hand; if it moves, it is not closed. On a model with a pinch or crush hazard, keep clear of the lid.
- Follow the edge of the gasket with your eye; if it bulges at one point, something is trapped.
- If a box or packaging touches the frame, correct the load and close again without pressing the lid.
- Write container ID, dispatch number, check time and checker on the form; attach a photo to the dispatch record where that is practical.
A half-closed lid does not raise the inside temperature at once, because the insulation absorbs the difference for a while. That is why the excursion shows mid-route, at the first delivery point, or never gets noticed at all.
In most operations the person who loads and the person who closes the lid are the same. Where a second person is not possible on every shipment, separate the two at least on mixed loads and multi-stop routes. The same check repeats for every lid opened en route, with opening and closing times entered on the form, because the check done properly at the first closing is usually skipped at the second and third.
Three things most often stop a lid closing: a load high enough to touch the frame, residue left on the gasket, and a container that does not stand flat and so twists the body slightly. If the same container reports a closing problem a second time in a short period, look at the container rather than the loading, meaning hinge or body; a short note kept against the container number shows this early.
