Bitzer help

[Harrison]

hi all,
i have problems on a 12hp coolroom system. The system was running with less than half its evaporators (coroded away!) and missing the high condensing fan for who knows how long. A while ago the "black box" temperature cutout was out and we assumed the cond. fan problem. Fixed that but motor current way to high (using 11kw instead of 8!) and evaporating way to low.
Replaced evaps, current back down to normal levels, but now the compressor is making a knocking sound.
On top of this the compressor has never (10yrs old) had an oil change!
Can people help with a plan of attack? gas change (r409a at momnet)? oil?
thanks in advance.

[wambat]

Clanking or banging compressor noises, at least the costly ones, are usually due to a loose connecting rod, piston pin, crankshaft, or other internal part. The compressor noise could also be due to refrigerant liquid "floodback" into the compressor crankcase. If this is the problem the noise will appear only at the interval of compressor start-up also a low oil condition in the compressor unit. You might want to pump it down to about 16 “ and see if it holds to ck the suction and discharge valves

[nike123]

First things first!
Knocking sound indicates possible liquid flood back. Check evaporator and total superheat while compressor is still alive !

[Harrison]

super heat is 10k (when the room is at 8 deg) at both the evaporators and picks up another 3 k to the condensing unit. bulbs are properly insulated and attached 45deg to bottom.
what is the result of liquid slugging in this type of compressor?
thank you.

[nike123]

super heat is 10k (when the room is at 8 deg) at both the evaporators and picks up another 3 k to the condensing unit. bulbs are properly insulated and attached 45deg to bottom.
what is the result of liquid slugging in this type of compressor?
thank you.

Result is something broken.

[Harrison]

something broken!! what, are you telling me you cant compress a liquid. so what would break?

[Peter_1]

something broken!! what, are you telling me you cant compress a liquid. so what would break?

You can never compress a liquid, that's since the beginning of earth.
Pistons, rod, and in worst case several pistons, pieces of iron will explode in the windings and on top of that, you will have a burnt motor.

[Harrison]

i was joking peter 1 but seriously, in practice liquid slugging causes such severe mechanical damage? i was thinking that a bit of liquid back would damage valves perhaps, but large quantities would obviously cause the said mech carnage!

[Peter_1]

I have others, pistons are twisted in their housings

[nike123]

something broken!! what, are you telling me you cant compress a liquid. so what would break?

If you click to "broken" in my response you will find what.

Here is another link!

Did you checked if oil level is to high? Do you have excessive oil foaming?
That also could be cause of knocking sound!

Bitzers are rugged and may tolerate small amount of liquid hammering (oil or refrigerant) for short periods.