Danfoss Scroll compressor failures

[PauliB]

Greetings - we have an issue with our swimming pool complex heat recovery airconditioners here in NZ. We have now had 3 out of 4 Danfoss scroll compressors SM185 failed - R22.( these are only 5 years old) Two had failed windings and last one draws excess current as though its jammed up.
The run fairly stable temps with acceptable superheat however I have also heard of these needing larger contactors than normal due to start current.

We have another pool complex that also had 3 out of 4 scrolls -R410a -( similar size -7 years old)fail although the second failure was because the previous fridgy thought it was clever to swap in a new compressor without doing an oil change on a tandem system!
Im concerned with these scrolls are failing within a short time frame with no obvious causes.

Any thoughts out there - has anyone experienced similar?

Thanks

[Glenn Moore]

Hi Paul
With scroll compressors the lubrication is often compromised with liquid refrigerant due to the oil never actually being warm enough to get the refrigerant out of the oil. Often scrolls are not fitted with crankcase heaters to save money and so during the off cycle refrigerant is diluting the oil. This refrigerant rich oil during start up is drawn up through the crankshaft the lower main bearing gets some lubrication whereas the top main beating and the scroll set thrust face only sees the residue of the vapourised oil/ refrigerant mixture which causes the top
Bearing to badly wear and the scroll thrust bearing face starts to scrap metallic particles and these particles are drawn into the motor air gap and cause a spot burn out or if the main bearing has badly worn there is rotor to stator contact and a major blow out. I saw a chiller with six SZ 185 which had run for less than an hour where all six compressors were wrecked . This unit was mounted outside a nuclear power station no cch's fitted it was the middle of summer . The contractor contacted me as he was concerned about the new machines. At this point I got him to fit cch's on the machines and told him to wait until the oil was at least 10 degrees above the ambient before starting the machines. After 2 days the oil temperature had not achieve the required temp. So I then got him to wrap the compressors with insulation jackets and 3 hours later all was ready to run. I then had to go yo site to hold the contractors hand as he was still panicking about the compressors. We ran the compressors and I re commissioned the system with a small tweak of the expansion valves to gain a little more duty and the plant cycle on and off without any problems. If you feel the bottom of the scroll she'll where the oil is laying you often feel the shell sweating due to liquid in the oil , the superheat is ok but the oil is badly diluted by liquid over feed during start up where the most damage is being done. Keep the shell and the oil warm and the scroll will last for ever. No bearings like running with liquid in the oil even polymer ones. With scrolls the oil has no means of becoming warm to boil the refrigerant out of it as the only hot area is the compressor crown and the hot oil in there is pumped out into the system not back into the sump. I have done this mod on many sites and have never lost a machine yet

[Magoo]

Hi Glen Moore.
a very informative read of your reply, I have to ask to obvious question " why are they not supplied with CCH's " from the factory.
magoo

[Glenn Moore]

Hi Magoo
Very good question its some sort of competition between maneurop and Copeland engineers who claim that their machines can cope with liquid . I had constant site failures on Scrolls and every time I cut the machine open the scroll set was smashed. I always recommend fitting cch's as bearings work better if the lubricant is good but when refrigerant starts to dilute it, it becomes an abrasive . On a scroll the scroll set thrust face when it is not properly lubricated , the refrigerant as it "flashes" due to friction it literally eats the thrust face cutting small ringlets out of the thrust face and these particles go on to kill the machine. Scrolls are great machines but can easily be killed by liquid , running into a vacuum etc I have some great pictures of the failed parts from scrolls, engineers just have to learn to treat scrolls with a bit more care.
By always fitting crankcase heaters and insulating the compressor shell to keep it warm is the best preventative maintenance you can do for a scroll especially if it's sited in a cold or windy environment at different times of the year. They won't overheat as they are suction gas cooled sometimes to much though Br Glenn