Intermittent Upright Freezer Problem
I've been a member of this site for about a year and a half, but this is my first question. Some background: I completed an HVAC/R program at a community college a few years ago, and I've been working on med/low temp equipment mostly in ice cream shops and other restaurants, as well as some small commercial AC.
So I have a customer with an upright Kelvinator freezer
model ULG30BSP-5 serial D2083725
404a 18 oz, txv Sporlan Y1232-FBS 1/4
copeland comp KAJB-007E-IAA (3/4 hp, 115 V, semi-hermetic)
Customer complains unit not cooling and says another tech told him he needs a new compressor. Customer wanted second opinion as he didn't fully trust the other tech.
When I arrive unit not running. Before trying to start, I check windings (1.4ohms, .6ohms, no short, not grounded). Check start cap, ok. Check potential relay normally closed contacts show very high resistance so I replace. Turn on unit. Compressor runs fine. I figure other tech condemned because it's not pumping right so I hook up guages and do comp efficiency test. Pulls vacuum, but doesn't hold. Customer doesn't want to pay for new comp because unit is not that old. I explain to him that I can replace the valve plate (I know, many folks here will say just replace the comp, but businesses are struggling right now and money is tight, and I've done a few they're pretty easy on the copeland k body comps).
I decide to pull the existing charge and weigh it instead of valving off system with the service valves. Turns out there is only about 1 (one) oz of refrigerant in the system! I leak check with 200psi nitrogen, sniffer, and big blue but unable to find a leak. I ask owner for service records because I want to know what is going on here! Still waiting on them...
So I replace valve plate, leak check again, evac to 500 microns, and weigh in 18 oz 404a. Start up and pull down. Check run amps at comp R terminal: 9.9A (normal). As box gets to 0*, I start checking subcooling and superheat, even though it's not quite down to temp. Pressures 203/8, SH 16* at txv bulb, SC 5*. But (this is where it gets weird) after a few more minutes, the compressor/freezer starts sputtering, knocking, and jerking, and the inside lights flicker a bit. One of the employess then tells me that sometimes the freezer "dances" like that and it drives them crazy. It turns out this is/has been an intermittent problem for a little while.
I turn off the unit and pull the plug and notice that they have it plugged into an extension cord. The extension cord prongs are burnt and black, and the original power cord prongs going into the extension cord are also very burnt. I figure that this is causing voltage issues, so I get them a new 20A/600V cord to specs, and replace it but this one is a couple feet longer than the original so we don't need a stinkin' extension cord. But this still doesn't solve the problem of the compressor "sputtering and shaking" (I know, not exactly technical terminolgy). Its not because of the mounts, and I double checked the electrical connections, terminals, wiring.. it all looks clean and tight. Discharge line doesn't have any obvious kinks. I keep thinking it is electrical because the lights flicker just a bit when this happens and it sounds like the compressor is "surging", if that makes any sense.
Anyone have any ideas? Could the compressor have intermittent mechanical or electrical problems that cause this? What am I missing? thanks in advance...
I guess the obvious question is, did you try a different outlet?
It almost sounds like water in the electrical....Could it be a control switch issue? maybe a faulty low pressure switch does not hold when the pressure drops but does not drop completely out...(chattering the compressor). You should be able to see the voltage drop if you check it from the cord to the compressor, fans, lights and whatnot...
Grasping at straws really...
On a separate note....Why do you guys always use so much pressure to leak check? I start at 40# with dry nitrogen and can count on one hand the amount of times I had to go higher...tiny bit of refrigerant, hit it with some N2 and scan it with the H10G....You could actually get a leak to stop with enough pressure sometimes (the molecules can fill the pinhole)....
Don't know if I helped...
I gotta get some shut eye.
edit; oooh, could it be overcharged with oil?, also, a capacitor issue should not be ruled out....
Yep, tried a different outlet, one that was running similar equipment.
Originally Posted by GT Jets
Changed power switch when I changed power cord.
No low or high pressure controls.
Put in new capacitor with relay (forgot to mention).
Nitro: normally start at 100, and work up to 150. Only go to 200 if not finding anything and it seems like I should (like if the system is almost empty!)
Overcharge of oil possible I guess but seems unlikely. Oil sightglass on this unit is pretty tough to read. <sigh>
Sounds like a cold control may be chattering? Tried to find a wiring diagram and struck out.
One way to outthink people is to make them think you think. They'll think you're not really thinking what you're trying to get them to think you think...........
Verify amp draw at compressor does not exceed RLA rating. Check voltage at terminals and watch for voltage drop as unit runs (wiring heatiing up) this causes potential relay to close and starts the shuddering you see. Check breaker and wall outlet. Try to have on its own circuit if possible.
Whenever I've seen similar symptoms, the problem has always been the start relay. Are you sure you replaced it with the correct one?
Copeland P/N 940-0166-08
The only other control that may cause it would be the temperature control as mentioned. I've never seen one do this, but it would be fairly easy to check out. I'd clip my meter across the control, set it for peak voltage and wait.
Thanks for the info
Thank you all for the replies. I'll double check everything and update the thread with results.
does the unit have a cpr valve or pressure limiting expanstion valve?
Update: verified correct relay installed. Also installed new protector in case contacts were getting pitted (although meter showed 0 ohms. Dang I do not want to be a parts changer!). Problem occurs intermittently, sometimes right on start up. When it does, current is twice RLA and start winding backvoltage bounces all over. Can also hear contacts in relay spazzing out. However, I quickly shut it down then restarted a minute later and it runs fine. Amp at 9.8 ok. Run winding 115V. Start winding steady at 87 V above the 55V threshold that energizes contacts. Checked all wiring. Rechecked windings. All ok. Don't think CPR or txv come into play on this. Controlled by electronic "Pulse" system which I'm not familiar with and can't find any documentation
Sounds like your losing your input voltage sporadically. Loose connection somewhere besides that failed extension cord? Control connections all good and no evidence of overheating through visual inspection? Voltage drop tests across relay and temp control terminals minimal? If I see voltage drops teeter to 1 VAC or more I expect a failing connection.
How old is the business location. I've come across electrical input problems that led to loose connections at the service panel breaker. Could be the breaker itself or bad neutral connection. Try an outlet you're sure isn't on the same breaker.
Back at the unit, make sure you neutral run inside it is good too. Could be something as stupid as a bad factory crimp on one of their wire terminals.
Refused to believe it needed a new pump. But it did.
Went back and checked voltage drops across everything between the power outlet and the compressor motor. Everything was fine, as was the voltage coming from the breaker box. Sometimes the compressor would run great for hours, with good pressures and amp draw consistent with copeland performance charts, and good winding resistance. Other times it would chatter the potential relay and never fully come off the start winding. So I replaced the compressor and the new one is doing fine. The guys at the supply house have never heard of a compressor intermittently failing and I wonder if anyone here has either. My theory is that motor bearings are worn/damaged in such a way that sometimes the motor is prevented from getting up to speed (thus unable to generate sufficient back emf), and other times the rotor is able to move correctly. Sounds crazy. I'm going to tear down the compressor and see what's going on inside.
Let us know what you find and i don't have to tell you to save the valve plate.
Originally Posted by mmmdave
Did you take a reading between the wiring and the case of the compressor with a megger?
I can tell you that often there is internal wiring issues that do not show with a regular multi-meter.
When I have electrical that I can not nail down or is intermittent.