Copeland Scroll advice

[Oceanlab]

Hi, just looking for some advice on this . . we have had a number of Copeland Scroll compressors causing unit alarms recently due to the internal thermal cut-outs failing and as they are hermetically sealed the advice from the manufacturer of the units they are in is to replace the compressors, but they are very expensive, I was wondering if there is any kind of external thermal cut-out device that we could fit in place of the internal? Any ideas?

[GREEK_REF]

First of all welcome to RE!! U can solve your problem quiet easy by calling a hvacr engineer!!!

[bjkmiami]

Hi Ocenlab!!
Can you tell me the models of these troubled compressors..because they have different type of protection depending on the model..

[Oceanlab]

Hi bjkmiami,

Thanks for the reply, the Model is ZP285KCE-TWD-265, the internal cut-out is wired to a motor protection device, the resistance readings are indicating that the thermal cut-out has failed and gone out of range, the customer says they are willing to run the Compressors with-out the protection device, which I have strongly advised not to do. Any advice?

[chemi-cool]

Hi bjkmiami,

Thanks for the reply, the Model is ZP285KCE-TWD-265, the internal cut-out is wired to a motor protection device, the resistance readings are indicating that the thermal cut-out has failed and gone out of range, the customer says they are willing to run the Compressors with-out the protection device, which I have strongly advised not to do. Any advice?

Please get some photos, this might be interesting.

[Oceanlab]

will try to get photos tomorrow, customer says that they are willing to run the compressor without the protection device as they have lost the compressor anyway, but my concern is what damage it may cause to the system if it does overheat and burn out

[r.bartlett]

I wonder why they have had so many failures and would like to prove it for myself by monitoring the systems over a period leading up to a trip.

If the sensors are at fault then a stat set at 150c strapped to the shell opposite the suction entry with a lock out relay would give reasonable protection against overheating

[bjkmiami]

Hi Ocenlab..
First of all ZP285 LCS range of scroll compressor comes with Kriwan INT69 external motor protection to keep the compressor from getting to the point where it is now..I am curious myself what exactly happened to this compressor and would be great if you can share any findings if you can manage...
These compressors have a PTC thermistor chain going through windings which is connected to the last PTC mounted to the top scroll for DT protection. So I assume this compressor was tripping out by means of kriwan every time ran into trouble before it got totally out of whack but was it high DT or ??? they may need the answer for their own safety in the future....
Also how did they check the resistance of the PTC chain and what are the values??
Good luck,

[The Viking]

Hmm,
Are the compressors running between trips at the moment or compleately dead?

There might be a valid reason for them to cut out.

Refrigerant charge, HP and superheat all OK?

[r.bartlett]

I am starting to think there is more to this than first impression...?

[Glenn Moore]

Hi Oceanlab
I have done a lot of work on Scroll machines and normally the Kriwan units work OK, but Scrolls are notorious for overheating by high discharge pressures, high suction superheats, low gas charge etc. This is why they fit the Kriwan units to safeguard the machine. If you are sure that the Kriwan sensors are damaged and no longer able to function then I would check that the motor windings are OK, and if they are I would then fit a DGT (Discharge Gas temperature sensor) which both Copeland ,and Maneurop supply this is a simple clip on Klixon device which measures the discharge gas temperature exiting the compressor . These trip at approx. 130 Deg C. This stops the scroll set and the lubricant overheating to the point of destruction. These are wired through the control circuit and must be wired in a fashion that when they trip the circuit locks out. The Klixon will automatically reset as it cools , but the system needs to be hand reset to prevent short cycling and engineer intervention as to what the problem is. If you can run the system for a few minutes a pressure and temperature log of the system would help us to help you further

[Oceanlab]

Thanks guys, the compressors do have Kriwan INT69 externally mounted protection devices which monitor the resistance reading of the internally mounted sensors, if the resistance reading gets to a certain point, they trip. Normally, there is always a resistance reading across two of the three pins depending on the compressor temperature, obviously. But, on these compressors that have failed there is no resistance reading from the sensor pins like they have gone out of range hence the Kriwan devices being open circuit. I am interested in these clip on devices, are they reliable Glenn?

[Oceanlab]

Also, the compressors are not constantly tripping as such, we are finding them tripped and showing no readings from the internal sensors, the resistance readings have been checked by three different multi-meters, all of which are calibrated

[Glenn Moore]

Hi Oceanlab
Yes these DGT's are simple but effective. Ive used them on several installations to protect compressors which have failed and been replaced due to system control problems.
Fit the DGT's and overloads on the start contactors and you can protect the machines from overcurrent and over temperature, these will give maximum protection to the compressors. But it is still important to check the system running conditions and rectify if necessary to give the machines a long happy life. The DGT's fit on the discharge pipe next to the compressor shell. I always recommend fitting these DGT's especially on heat pumps as whatever the problems on scroll machines the first thing that normally happens is the discharge temperature sky rockets causing the scroll set to distort and the motor to overheat BoL Glenn

[bjkmiami]

Thanks guys, the compressors do have Kriwan INT69 externally mounted protection devices which monitor the resistance reading of the internally mounted sensors, if the resistance reading gets to a certain point, they trip. Normally, there is always a resistance reading across two of the three pins depending on the compressor temperature, obviously. But, on these compressors that have failed there is no resistance reading from the sensor pins like they have gone out of range hence the Kriwan devices being open circuit. I am interested in these clip on devices, are they reliable Glenn?

Hello Oceanlab,
what do you mean by two of the three pins??? are you talking about the leads motor windings are connected(T1 T2 T3)?? if so they are measuring the resistance of windings not the PTC chain!! PTC chain leads are connected to the the kriwan module via terminals S1&S2. Normally you should read good resistance on PTC chain like couple hundreds ohm..Nevertheless if you are reading ''0'' on one of these it is not a good news at all!!!that means you have a shortage...and there is not much you can do about it.. As far as using DGT sensor yes it may do the job for protection against high DT but keep in mind by bypassing kriwan protection you are not ONLY ignoring DT, you are ALSO vulnerable to phase loss and incorrect phase sequence...
Good luck,

[Oceanlab]

Hi bjkmiami

These 3 pins have a plastic connector attached to them, this connector then has two cables coming out of it which go to the kriwan device (connections s1 and s2)so that it can monitor resistance, it is kind of hard to explain, I shall take some photos next week and post. Thanks for replying

[GREEK_REF]

hi to all
Oceanlab sorry for my previous answer i thought u are end customer! my experience on the same problem says that you have few choices!!
first be sure that the internal sensors are the problem and not the external.
sometimes the exeternal module stucks and if you hit it gently with a screwdriver works for a few minutes maybe not!!
buy a new one and mount it to every compressor to find which faults.
in case of faulty DGT replace it.
in case of faulty internal sensor instal a phase protection to the power line to protect all the compressors then bypass the DGT and calibrate the motor protection circuit breaker with no tolerance optional u can place a discharge temp sensor in row with the circuit breaker

good luck
christos

[Oceanlab]

Hi Greek_ref

Hit it with a screwdriver? haha I like that I have swapped the kriwan device from a compressor that was running ok and still the same problem. The good compressor to which I have then placed the kriwan device from the suspect compressor to then runs fine, proving the kriwan device is ok, also when the resistance of the internal sensor in the compressor that is running ok is measured, it always reads a value depending on the compressor temp, but with the suspect compressor, there is no value read across the terminals indicating that the internal sensor is defective/out of range/shorted and as the compressors are hermetically sealed, the internal sensor can't be replaced, just wanted advice on this.
Thanks for replying

[Dimitris]

Hello there.
Did you check the refrigerant cycle thoroughly? I mean superheat and subcooling ?

Best regards