Copeland Scroll not pumping

[skarrs71]

Good evening Ladies and Gents, my first post here, but I have read a previous thread on here regarding this issue and would value some input on a similar issue. I work in the dairy industry and was recently called to a milk tank being slow to cool, on arrival on site at start of cooling I found the compressor to be starting without a long enough delay on start of cooling and consequently icing up the evaporator and showing signs of liquid flood back. Turned compressor off and left for 30 mins until sufficient milk in tank to cover evaporator plates and system seemed to be functioning correctly, evaporating around 10 degrees c below milk temp and cooling ok, can't remember exact readings. I know the system requires a longer start delay, but requires laptop and software to alter parameters, which has not yet been done, but will be at soonest opportunity when person with software is available. I have since been back on site to find the compressor not pumping, discharge and suction pressures equalized, with motor running, model ZB114 3~ 400V load around 12-13A, which having taken account of previous findings I diagnosed as smashed valve reeds. In retrospect having read previous thread I would suspect the scroll has disengaged from motor since if valves were smashed I would expect the compressor to be too hot to touch. We have a new compressor ordered for site but I am loathe to replace if it is not the issue. The circuit has 2 evaporator plates with the suction and liquid lines t'd off close to the tank so difficult to tell superheat settings of each plate, I suspect one of Sporlan TXVs to have failed? but any advice on how to diagnose which one (or if i am barking up the wrong tree) would be appreciated. Another of our guys has been back out to this since and found the compressor to function ok intermittently, but soon stop pumping again, although he didn't take pressure readings!

[monkey spanners]

Fabdec by any chance?

Common for the Power element to rust out and shut the valve on those Sporlan TXV's, Probably worth changing if they look rusty, also check any inlet screens as have seen them block up depending on how clean the system is.

Theres no valve reeds in a scroll, just a check valve. I think some have a valve that if the scroll overheats its designed to bypass discharge back into the suction side to make the klixon trip, possible if the TXV's are underfeeding the compressor is overheating.
Its also possible its suffered wear due to pumping liquid if its been going on long enough, or wear due to low oil if indeed one of the TXVs is faulty as the lack of flow can log all the oil in the evaporator.

Copeland Scroll™ – How Scroll Works - YouTube

[skarrs71]

Thanks Monkey Spanners,

Indeed Fabdec, and yes the power elements are pretty corroded, farmer has decided (or been talked into) replacing complete valves on both circuits, pet hate of mine ripping customers off when only the power elements need changed on one circuit, or probably only 1 power element, but heyho.

Wasn't aware of the lack of valve reeds, so thanks for the heads upon that, I know the relief valves can pass but only time I have actually seen it is if the lp cutout is set to low and the scrolls tend to bounce on lp if the differential lifts the relief valve.

Confused me because the compressor was reported to be running fine for a while before stopping pumping, but when monitored "working" found suction to be way lower than expected hence I think only one of the pair of valves on the circuit has actually failed, which has lead to the motor overheat and disengage of scroll due to lack or refrigerant returning to cool the motor, I think I have this reasoned out right now, but feel free to correct me lol. Another case when spending (being allowed) more time analyzing may have actually worked out cheaper for the customer!

[Jeff Winsor]

When the power elements fail they shut down causing low pressure.
Easy to check with surface probe thermometer after the valve .
If 2 txv on one compressor easy to compare the 2 against each other.

[sendhilkmar]

If the scroll has a sticker of ASTP indicating internal by pass then there is a possibility at low pressures only motor runs with internal bypass . I have experienced the same in bulk milk cooler whereas the milk quantity was less than 25% of tank capacity and LP switch setting was too low .
If ASTP is activated then it is reversible after sufficient amount of cooling off time; if that's not happening then there could be irreversible internal damage that needs replacement .