Most common reasons for freezing up?
I am relatively new to refrigeration, I was a residential HVAC tech and decided I wanted to get into Commercial HVAC and Refrigeration because I was getting tired of the salesy world of resi HVAC. So I am very good at diagnosing refrigerant issues with residential equipment and RTUs because I am used to those pressures and basic rules. I work in restaurants primarily.
But I am new to the refrigeration side of things so I have some things I’m confused on. I work with guys who I honestly think don’t know as much as they should by now. They all have different opinions on things, and some of them don’t know what superheat or subcooling even is, and they don’t use saturation temps in their diagnosing. They go by pressures only, and some of them don’t understand that if a box is hot the suction side will be higher because of the heat load sucking into the evaporator.
How do I know if a system is truly low on refrigerant? I usually go off of my saturation temps and compare the air temperature that is moving through my coils, as well as using the sight glass to make sure that my metering device is being fed liquid. It’s my understanding (I might be wrong) that our vapor saturation should stay somewhere between 10-20 degrees Lower than the air moving into the evaporator to keep the air getting colder and colder. And our liquid saturation should stay 15-25 hotter than the outside air moving into the condenser coil. I also know that the best place to check superheat is right at the coil, and I usually look up what each evaporators recommended superheat is by the manufacturer.
I’ve had evaporators that freeze up like the one in the picture multiple times, but when I check pressures and sight glass and superheat, everything will look great. And the drain is draining correctly. I usually then I always look at things like door gaskets and humidity intrusion factors and the only answer I can come up with is “maybe there opening the door to much” but that makes me feel like I’m guessing and not a good tech. I just want help and opinions on the best way to diagnose freezing walk in evaporator, and even reach in evaporators that use 448 or 404 or 22. I’ve even added defrost clocks to some of these coolers with 4 defrosts a day and they still freeze up 3 weeks later. But when I thaw them and run them again everything looks normal and they meet temp really quickly and pump down like they should.
If anyone could give a new restaurant refrigeration tech some tips that would be greatly appreciated, because one day I might go into bigger refrigeration and I want to know these rules before making a bigger leap in the future.