Best sensor to use to determine cooler maintenance

Hi

My company is tasked with doing maintenance on refrigerators in convenience stores.

We are interested in gathering data from those coolers, however I am not sure how to approach this.

So the basic question is: what data/sensors must I use to determine when a particular refrigerator should be visited?

I know that we can take temperature sensor, and there is even a sensor to detect R134 gas leaks as well. Would they represent enough basis to determine that fridge A is faulty and need repair?

Anyway other sensor that is more suitable for the job?

Typically fans fail and then the refrigeration coils get clogged by ice, therefore the compressor has to run for longer to keep the temperature down. Also in display cabinets, condensate drains get clogged and the bottom fills up with water which causes the fans to drown and stop working.

So you could measure the RPM of the fans, the speed of the airflow through the coil, the run time of the compressor and the water level at the condensate drain entrance.

My own observation is that none of this is done in real life. Employees react to a high temperature alarm, or flooding by doing a visual inspection of the system, then call a repair tech.