Display Cooler Issues
I am a second year apprentice Hvac technician. I have a "A" gas ticket and mostly work on A/C rooftop units. I live in the NWT and am currently having issues with a open front dairy cooler in a town approximately 2hrs drive from where I live.
There is a single 404a compressor with an accumulator and a receiver feeding two seperate open front coolers both different sizes, one is approximately 1.5 times the size of the other. The coolers are equipped with seperate solenoid and tx valves, one cooler has 2 evap fans and the other has 3 fans. The condensor is outside and is a single unit for 6 seperate compressors.
I originally went and diagnosed low refrigerant as the suction pressure dropped of immediately when the compressor came on and then the compressor went right back down again. I added some refrigerant and coolers came right down in temperature and stayed down. I monitored for approximately 2-3 hrs and then made the drive back home... 11 hrs all told. My journeyman walked me through the process.
The cooler went down again overnight and the next day my journeyman made the trip solo to follow-up. He informed me when he came back that he found a small leak on the high side pressure hose that goes to the pressure control and also that he found a high side regulator on the system. He set-up the system to operate at 210psi high side and approx 12psi low side. He then shut down the unit and removed the hose and ordered a replacement hose. My journeyman then went on days off
I received the replacement hose about 5 days later, again made the trip to the grocery store and installed the new hose. I turned the unit back on and all seemed good. High side pressure of the compressor 210psi, low side pressure 12psi, coolers cooling... monitored for 3-4 hours as the community is so isolated, all working good.
Sometime the next day the cooler went down yet again
This time no power to compressor. We happened to have a plumber/gasfitter in the town at the time and conveniently he was able to troubleshoot the electrical via phone with me. All windings tested OL to ground and windings gave proper readings. It was two phasing through the contactor, one leg of power on the three phase was not making it out of the contactor. Replaced contactor. Compressor came right on and coolers immediately began cooling. As the tech was not refrigeration, he could go no further, not tools and came back. Store phoned again this morning saying compressor was running, but no cooling taking place... cooler at about 15 degrees celsius. He also advised me that he could not see a level in the oil sight glass on the compressor, though he didnt know what it was until I told him it was for checking oil level. I requestsed he shut down the compressor until I get there to prevent damage to the unit.
I have e-mailed my journeyman and am awaiting a response. I am going there tomorrow to work on this cooler again, but as this is one of my first coolers I am looking for advice. Please!
12 psi with R404 = -26* SST TOO cold for dairy cases. If its down again I suspect a leak you are missing. Its also possible that the contactor installed by plumber was not the correct part? This post needs some more info for any accurate help. Your best bet is to drive out and see whats up.
You mentioned you have one compressor for two cases with two separate solenoid valves. Are they controlled by the same thermostat, or do they have separate thermostats? If they have separate thermostats, it is a crappy setup that I see way too often.
If one thermostat satisfies, the solenoid closes and pumps out its evaporator. You now have way too much compressor, which will lead to low suction pressure, low superheat, and very possibly short cycling. Have you verified how the solenoids are controlled?
So... I found secondary liquid line filters inside each of the two open front coolers just prior to the TXV's. Talking with the store manager found that these were refurbished coolers when istalled into new store. The filters were restricting flow and there was a temperature drop of 50degrees ferenheit across the filters. I pumped down and removed filters and replaced with straight pipe. Vacuumed down system and then returned to operation. High side 210psi... low side 43psi... everything working just great. Thanks for the tip on the low side pressure... led me too look for a restriction in ther piping!
Originally Posted by TroubleCooler