Defrost is a normal cycle that clears frost from the evaporator coil. According to the Thermo King T-Series manual the unit passes hot refrigerant gas through the coil, the melt water runs out through the drain tubes, and a cycle started automatically or by hand ends by itself once the coil passes 11 °C.
What rises in the record is the air temperature. Air shows the cycle at once, while product, with its mass and packaging, warms far more slowly; how much depends on the length of the cycle, the size of the product and the loading pattern. So the air curve does not answer the question, the reading next to the product does.
- Take the start and finish of defrost from the unit's log and compare them with the logger clock.
- Read return air, supply air and the product-side record separately; write down the logger's position, interval and calibration.
- Put defrost on the same timeline as door openings and loading, and add a note beside the raw data rather than deleting anything.
- Check whether the rise also shows in the product reading and whether the required temperature returned after the cycle.
The manual recommends a manual defrost 30 minutes after loading and after each en-route inspection. If cycle frequency or recovery looks different from what is expected, take the unit log, measurements and model details to technical service; protection and defrost settings are not changed without authorisation.
