I do some lurking here but not much (ever) posting but I now have a problem that I’m hoping to get some suggestions for. I run energy management equipment that controls (amongst other things) cycling etc of solenoid, evap fan, and defrost heater for several walk in freezers and coolers. One freezer has experienced a lack of capacity during warm weather although the load calculations (admittedly fallible) show that the unit should be more than sufficient.
The equipment is less than two years old and the problem has existed since new. A similar unit beside this one has relatively less capacity but works properly. Equipment was changed to upgrade the refrigerant (as far as memory serves). One thing I have noticed is that this unit in particular shows TXV hunting as reflected in the suction pressure during a normal run cycle. Suction pressure is monitored with a transducer.
The suction pressure of two comparable walk in freezers that don’t seem to have capacity problems do not show this symptom. So far, our refrigeration contractor and a representative from the component supplier have been unable to recommend a solution. The TXV bulb is well wrapped and secured firmly to the suction line in the 4 O-clock position about a foot from the coil.
The hunting is continuous and has a range of about 1 PSI. 1) Is 1 PSI hunting more than normal? 2) Could this cause a capacity reduction? The outlet pressure might be straight into the evaporator or into a distributor and onto distributor tubes and then the evaporator. Of course, superheat has to be set at design conditions, the first of which is the designed full evaporator load. The air on temperature has to be brought down to design conditions. Then you check to establish design head pressure and design liquid temperature.