View Full Version : oil failure problem
08-03-2004, 05:11 PM
Two carlyle 06d compressors twinned together with a common oil line between them. The application is a walk-in freezer maintaining below 0F using R507 & POE oil. Thermostat/defrost control is a Johnson digital with remote sensors, controlling lls for pumpdown. Defrost is 30min every 6 hours timed termination (electric). I receive a call that it's not keeping temp. I ask the customer if the oil failures had tripped, yes they did when he reset them, three times they failed. That was yesterday at 2:00pm twice and the third at 11:30pm. Today I get there around 8:30am and reset both controls. Take oil pressure, 19-21psi net. Oil S/G is half full. I tried to simulate a situation where one compressor would run and not the other, it didn't trip. I couldn't force these compressors to trip. My only conclusion is that there wasn't oil in the crankcase yesterday, and for some reason there is today. Is it possible for the oil to slowly return overnight? If so, am I looking at a piping problem? Why overnight and not between 2:00pm and 11:30pm? Thay have a blast freezer in this box as well, so thay let that run to maintain temp.
08-03-2004, 06:02 PM
Check your pumpdown low pressure controls to be sure they're shutting down during defrost and the off-cycle periods.
Check your compressor contactors. A bad contactor can cause oil failures when the pump fails to start.
Look for possible causes of floodback, either at startup or during operation that could cause oil dilution and loss of oil pressure.
Eliminate all the possibilities of why or how they could trip the oil failure control with adequate oil before assuming the is no oil. ;)
08-03-2004, 06:10 PM
Thanks for the reply...
Pumpdown lpc are working.
Contactors are good, oil failure is 240 volt, inseries with coil, compressor is 600volt
Watched both compressors for 3 hours, with a complete defrost cycle and back out of it. Didn't notice anything abnormal
08-03-2004, 06:32 PM
As far as you know, are the oil failure trips occurring consistently with always both compressors going out or with only one?
I know it's really tough to rely on info from maintenance workers, but sometimes there are guys that are quite helpful......especially if you've had a few years to "train" them in what to look for before they start pressing buttons and stuff. ;)
08-03-2004, 06:39 PM
Well, he said they were both tripped all three times and they were both tripped today. I got to believe it's an oil problem and not a compressor problem at this point. I'm thinking piping may be a problem. There is a sution trap at the evap, then the piping goes directly up about 10ft. It goes out the wall then back down about 20ft. into the mechanical room, where the compressors are. It looks like it is piped properly, but maybe the pipe is too large inside diameter, I think it's 1 3/8".
08-03-2004, 07:06 PM
You reset both compressors this morning and the oil SGs were half full. That oil didn't move there by itself overnight. I don't see this as an oil return problem or even a low oil level problem at all. Something else is happening here that we not recognizing just yet.
Are they running that blast freezer system at the times when this system is going down? What's the box temperature doing at these times? Can you get some data recorder on these units to see what's happening? You might want to monitor discharge temperatures for instance to see if you're getting serious floodback just before shutdowns.
08-03-2004, 07:27 PM
They only run the blast in critical times, like this, it rarely runs. Sometimes when they are doing a lot of production and they are in and out of it, they will run it too. They have a temp. recorder dial for product insurance, by the way this is a fisherie. I noticed a change in consistency around 8:00am yesterday, they probly didn't notice it until 2:00. It went into defrost, came out and dropped very slowly and only about half of what it would drop on a regular cycle. Then it went into another defrost and never recovered, that's when they ran the blast. Then the temp dropped and stablized. Clearly something happened during that defrost where it couldn't reach temp. The question is what? Whatever it was, effected the oil failure, tripped it and kept if off.
08-03-2004, 07:44 PM
So it sounds like one pump is tripping out after a defrost and then the second one goes down after the next defrost cycle. This would lead me to expect some really bad flooding post defrost. You say you didn't see anything unusual during your observations, but I'd likely be clamping a discharge line temp data recorder on this beast right about now......or maybe tomorrow AM. ;)
08-03-2004, 07:56 PM
Ok, so you think after defrost, the system is flooding liquid, washing out the oil and failing on oil pressure? That makes sense to me, except the high discharge temp. Could you explain that one? Will the temp recorder prove a floodback? Also, what would cause that flood back all of a sudden? A bad TXV? What could I do to solve the problem?
08-03-2004, 08:08 PM
I would go for watching the discharge temp only because unless you have a sophisticated multipoint data recorder you would have a hard time monitoring suction conditions that would indicate floodback. The discharge temperature will show up really low during a flooding condition and will be the better telltale to watch IMHO.
refer dude 2479
08-04-2004, 12:26 AM
One other point that is off of the line that you are focusing on is this..
Carlyle oil pumps are weak at best when new. They are not a true positive displacement pump but rather a simple ocillating piston on an eccentric. How old are the compressors. If they are older than a few years I might suspect that the oil pumps are worn and loosing prime under high loads after defrost due to slight or moderate flood back. Carlyles are the hardest to catch on random oil fail trips.
08-08-2004, 08:03 PM
I had a copeland kicking oil safety years ago on low temp
many times. Found a feedback through the 220v oil safety heater to #4 condensor fan motor with a partial winding ground letting the heater get 110v to ground at times. Changed the motor. Changed the factory oil switch wiring. Study your wiring diagrams as you might have a floating ground in the heater circuit wiring letting the heater turn on with 110v
but it will take longer than 45sec to kick off the safety depending on the ambient temp
I know I should have kept that diagram for proof To late now
Wow my first post as i couldn't stand to lurk forever
thought maybe i could help someone
08-08-2004, 08:49 PM
I don't know about Carlyle but on a single suction cooled Copeland if you have severe blowby the pressure in the crankcase is greater than the pressure in the motor cavity and the oil will not go through the check valve between the two areas to refill the crankcase and will run out of oil, cycle off on safety and then refill after the pressures become greater in the motor cavity equalize through the check valve and then show full when you get there. Adding oil will not help and infact you may slug the compressors but if you have worn cylinders you need a scheduled replacement anyway. You have to catch it running low on oil and turn it off and watch the oil level rise. Copeland people have told me that there needs to be 1/2 pound difference between the two areas to make that check valve open and allow oil back into the crankcase and you can't see a 1/2 pound difference with standard gauges
Increasing head pressure will increase blowby percentage too
and hold oil in the motor cavity
But if you have oil separators this may not be happening but it could if all the reserve oil stops in the motor cavities
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