We've supplied a condensing unit with falling film evaporator, year back.

Since then, we've replaced 4 scrolls, 1 after every 3 months.

Comp is copleland ZR-300KC-TWE- 25 HP - 575V.

Tear down report says that oil is diluted, scrolls spun, etc.

After every replacement, the subcooling, superheat, amps draw, discharge temp, etc was checked, they were always in limits.

The compressor oil seems to be black after failure.

The oil seems to be little acidic.

After 1st failure, LL sight glass becomes blackish in colour, which is better now.

The suction and liquid filters were replced after every failure with charcoal and high water capacity cores.

Oil is checked frequently, which at 1 point seems ok but later becomes acidic.

System has HG bypass and pump down option.

Pump down is done down to 15 PSIG.

System pressures are 55/220 PSIG with R-22 refg.

Timer is installed in series with LL soln for 10 mins.

System is indoor, complete with CC heaters.

Sometimes, comp runs for few mins. and stops due to open flow switch.

Besides this, there is another system with same design and running under very similar conditions with bitzer recip.

This is running perfectly since 1 year.

Does the scroll system needs new refrigerant and system flush?

Is too many starts could be problem?

Is shorter running time could be issue?

Still couldn't figure the actual problem!!!