Deli Cases, Regular Headaches...
I'm an HVAC tech that has been dealing with some deli cases and the like for a regular customer. The most recent is a McCray 8 ft double duty unit. It's history includes being converted from R12 to 134 sometime in the past. Also, the compressor has been replaced at least twice in the past 3-4 years. Unknown before that.
I found it with.....a bad compressor. I got a new replacement compressor and did a heave R11 flush to the system, including the TXV separately.
I followed it up with triple evacuation and evac to 1000 microns and made sure it held for 30 min.
Charged the system and started it up. Seems to run well now, but trying to get it to cycle correctly. I was surprised to find that the only method to control the case temperature is by the low pressure switch.
I'm wondering if I can't get better temperature control by using an adjustable thermostat and set the pressure switch to shut it down as a low pressure control should.
Also I'm having trouble getting the range of pressures I should be operating in. Going by the specs for newer units, I'm finding a suction pressure of 14-18 and a ll pressure of about 115 is what I should expect. I may be a bit overcharged because my pressure runs 20-22 at times and my suction line freezes at times.
I also read to look for a superheat of 10 degrees, but this case is controlled by a TXV so I'm assuming a subcooling reading would make more sense,but don't know where to find that. I'm also assuming any readings should be when the case is down to temp.
I can find no manuals for the unit, only a spec/tearsheet on the mfr website.