Scroll smashed in compressor during pump down

[Jasper]

HI all

One of our engineers recently carried out routine maintenance at a site, during a pump down test to check LP cut out point there was a loud grating noise and then one of the compressors stopped running!
The compressors on the circuit are tandem 25kw Sanyo scrolls running on R410A for close control application.

We suspected that the installing contractor had not put additional oil in the system even though the manufacturer had insisted they should add additional due to the extended pipe run (40>50M)

The compressor was removed and sent for analysis,
Suggestion from the compressor re-manufacterer is that "Both scrolls and the discharge valves are smashed, the main bearings and crank shaft are ok; Liquid slugging could have occured which could explain the lack of oil in the compressor and the damage to the scrolls and valves"

My question is; How could liquid slugging have occured during pump down? the liquid line would have been closed at the service valve, so no liquid refrigerant would have been able to carry over to the compressor!

Your expert thoughts on this would be greatly appreciated.

Regards

Jasper

[brunstar]

well depending on the refrigerant quantity in units, most people think that you can pump down any system and vrv, in fact when you think about it, where is the system supposed to store the additional 30kg of refrigerant, it is dangerous and each job should be looked at to see how much additional refrigerant is in the system, especially with R410.

[nike123]

Lets try one scenario!

Cold day and crankcase heater not energized for few hours. Refrigerant migrated to cold crankcase and condensed there. Suction valve closed before compressor started and after compressor started, we have rapid pressure drop on suction side. Refrigerant wildly boiling below oil film and huge quantity of oil droplets get in to scrolls. Now we have liquid in them and probable liquid hummering has broken scrolls and valves.

How about this scenario?

[Jasper]

Hi nike123

Compressors are located internally, remote condensers, so should be minimal migration!

[brunstar]

if it is turned off it will still migrate until warmed.

[Brian_UK]

Was the system/compressor operating when he started his pump down ?

[powell]

HI all

The compressor was removed and sent for analysis,
Suggestion from the compressor re-manufacterer is that "Both scrolls and the discharge valves are smashed,

Interesting, Sanyo scrolls have discharge valves.

[Jasper]

Both compressors running under manual control prior to pump down.

Could low oil levels in 1 compressor allow an oil slug to be pulled through the oil balance line of compressor 2??

(just thinking aloud)

[Jasper]

More pics of damage

[Brian_UK]

Interesting, Sanyo scrolls have discharge valves.

OK, so maybe not discharge valves but most have a check valve valve in them.

[lowtempman]

Perhaps problem was related to high temps as well as a lack of oil. High compression ratios occur at pumpdown. Maybe the LP switch was set wrong or inaccurate allowing excessive pump down. You said the procedure was to check the LP anyway. At high temps could the scrolls have heated enough to expand to the point where they rubbed, [hence the scraping sound?] I don't know that much about scrolls but if the clearances are similar to screws it is ijn the neighborhood od a FEW THOUSANDTHS.

[icemakerman]

i was recently advised ...due to higher volumetric efficiency in scrolls that they should not be pumped down... they will start to pump out oil and fail!!! just a possibility this may be the case

[Brian_UK]

I thought that also, but could only find this about electrical failure...

CARLYLE commercial scroll compressors should never be used to evacuate an air conditioning
or refrigeration system. This is because of the high volumetric efficiency, which
can cause extremely low vacuums when the suction side of the compressor is closed or
restricted. The low vacuum pressures may cause internal arcing at the electrical terminal.
This could result in a failure of the hermetic terminal and ultimately a vented pin.

[powell]

Jasper,

Check out this link to Copeland's bulletins. Click on "Flooded Start" and scroll down about half way.

http://www.hvacrinfo.com/Cope_quick_ref.htm

Hope this is educational to ya!

Powell

[Jasper]

Thanks Powell

[neocool]

You should also check the crankcase heater to make sure that it is working properly