Compressor Liquid Return R-404A washing Oil

[georgedvf]

I have a broken Semihermetic Compressor diagnosed for 'Liquid Return' that washed the oil. This are the damages encountered:
1.-Scratched pistons. (I'm not English native so please correct)
2.-Scratched and premature wear of Oil Pump.
3.-Excesive wearing on bearings/bushings.
4.-Overheating of Valve Plates.
5.-Excesive wearing on Tie rods.

Are this damages encountered enough to determine the cause of damage was 'liquid return'?????

Also I thought that the Oil Differential Pressure Control (Jhonson Controls P545NCB-25) had the ability to protect against liquid return, I'm I wrong?

Thank you!

[Emmett]

You are mistaken, the oil pressure safety protects against loss of oil pressure, you would have already incurred damage from liquid return before you lost oil pressure. curious, why did you have liquid retun?

[chemi-cool]

That the result of no lube to all these parts.
You lucky no rods and valves broke.

[georgedvf]

You are mistaken, the oil pressure safety protects against loss of oil pressure, you would have already incurred damage from liquid return before you lost oil pressure. curious, why did you have liquid retun?

Could you explain me why? Are you saying that liquid refrigerant goes through directly into the pistons and there's still oil on the carter so the pump still has oil to pump? I thought the liquid refrigerant washed the oil on the carter first.
We're still trying to figure out what happened, 'liquid return' was the diagnose of the Compressor manufacturer (they didn't even check the entire system, superheat... nothing) I'm not so convinced about their diagnose so I'm trying to research more.


That the result of no lube to all these parts.
You lucky no rods and valves broke.

I agree, but aren't there other reasons that could cause non lubrication?

[Emmett]

Could you explain me why? Are you saying that liquid refrigerant goes through directly into the pistons and there's still oil on the carter so the pump still has oil to pump? I thought the liquid refrigerant washed the oil on the carter first.
We're still trying to figure out what happened, 'liquid return' was the diagnose of the Compressor manufacturer (they didn't even check the entire system, superheat... nothing) I'm not so convinced about their diagnose so I'm trying to research more.
No I'm saying that the liquid refrigerant could easily cause the discribed damage prior to a loss of oil pressure, liquid refrigerant will wash the oil out it is just not instant and the damge could have occured before the oil was gone resulting in oil pressure loss, furthermore there is a timing device which for oil pressure is typically 2 min.


I agree, but aren't there other reasons that could cause non lubrication?

Yes there is, the oil could have slowly migrated to the evaporator.

[D.D.KORANNE]

there will be various reasons for liquid carryover to compressor
1.0 exp valve stuck open
1.1 super-heat of ex valve too low or disturbed / altered /
1.2 evaporator unable to evaporate all the liquid due to contamination
1.3 chiller pump / air handling unit fan , rotational direction altered
1.4 too low load on evaporator
etc

a simple way to arrest liquid slop over is to instal a suction accumulator ( a solution not too good but can help you save compressor in the unforeseen events like decribed above )

[georgedvf]

No I'm saying that the liquid refrigerant could easily cause the discribed damage prior to a loss of oil pressure, liquid refrigerant will wash the oil out it is just not instant and the damge could have occured before the oil was gone resulting in oil pressure loss, furthermore there is a timing device which for oil pressure is typically 2 min.

Is it possible to notice a gradually loss of pressure at the injection pressure of the pump, I mean, it is supposed to be about 60psi at injection (if oil is being pumped), would I read continous lowering of this pressure if liquid refrigerant is returning to the compressor???

[Emmett]

I think it depends on how much liquid is returning! the more liquid is returning the quicker the oil will leave the sump and the sooner the oil switch will trip, however the more liquid returns the more likely it is that severe damage to the compressor will occur.

[NZPOMME]

Just a thought, have you got the correct oil in the system? have you done any modifications to the system recently i.e change the gas? has the system got a oil return! if its a semihermtic there must of had a fair bit of liquid to come back to do that damage in one hit, does the unit run through the night as if its switched off then maybe you have had liquid migrant to the sump! how big the system!! another way of stopping this is a C.P.R! does your sump heater work!

[georgedvf]

Just a thought, have you got the correct oil in the system? have you done any modifications to the system recently i.e change the gas?
It is Polyolester (BITZER BSE-32) I think is the right one for use with R-404A, and no the system has not been modified on anything.

has the system got a oil return!
Yes, it has oil separator at discharge with good level on it.

if its a semihermtic there must of had a fair bit of liquid to come back to do that damage in one hit, does the unit run through the night as if its switched off then maybe you have had liquid migrant to the sump!
No, it operates normally at night.

how big the system!! another way of stopping this is a C.P.R! does your sump heater work!
It is a 330MBTUH system, 2 evaps. and yes the heater is working ok.

[georgedvf]

Another discovery we did last week when checking the history of operating conditions was that during Defrost, when the solenoid valve closes, the compressor is supposed to cut off on low pressure but it doesn't, the pressure control is broken, so the compressor kept working during Desfrost lowering the pressure down to 0 psig and even negative readings.

This happened about 3 defrost cycles of 10 to 15 minutes every day for like two weeks before it broke up.

Do you think this could caused the oil to get out of the compressor in that period of time so the damage was caused because of this low pressures???

[chemi-cool]

looks like you put your hand on the problem, Too low pressure = low flow speed of the refrigerant = no oil return.

[monkey spanners]

Is the discharge check valve working ok?

[georgedvf]

looks like you put your hand on the problem, Too low pressure = low flow speed of the refrigerant = no oil return.

I agree, even if there were not too low pressure the solenoid valve is closed, so there's no oil return at all. Also I'm not sure but I think that too low pressure on the compressor makes the oil to get out of the compressor, am I right?


Is the discharge check valve working ok?
I think so, why???

[monkey spanners]

I think so, why???

If the check valve lets by it can allow liquid to come from the condenser into the oil seperator and the float in the seperator can't tell the difference between oil and refrigerant so there is a risk of liquid refrigerant being dumped into the sump during the off cycle if the check valve is faulty.

[georgedvf]

That's true, but the compressor didn't shut off during the defrost cycle, this couldn't happened right? (low pressure control was faulty)


looks like you put your hand on the problem, Too low pressure = low flow speed of the refrigerant = no oil return.
Does 15 minutes of compressor running with the solenoid valve closed is enough to empty the oil in the compressor? I don't know much about the oil out-return rates...:eek:

[monkey spanners]

Don't forget any times it tries to pump down when its reached temperature, it would have been running in a vacuum then too.

[georgedvf]

We didn't use pump down for temperature shut down, it has EPR and controller shuts down directly the compressor. In fact it is a parallel compressor rack, but right now there's only one room in use, only 1 of 4 compressors is running and all other circuits and compressors are closed.

[georgedvf]

So, do you think that those periods of time (defrost) when the compressor went into vacuum because the Solenoid was closed were the reason to lose of lubrication on the compressor???

[Magoo]

The compressor would also be running very hot without gas cooling effect, which in turn raises the oil temperature, lowers oil pressure and both effects causes excessive wear on bearing and piston surfaces. Even though the oil pressure is still/slightly above oil pressure cutout pressure.

[georgedvf]

Ok, that's good info. We took an oil sample to test for acid and it was clean.

Do you think that because it was short periods of time when this happened the oil didn't degrade itself?

[D.D.KORANNE]

In the event that liquid line sol valve shuts off and comp does not trip on lp , and comp operates for 15 minutes or so the semi-hermetic gas cooled compressor will heat up . This could also contribute to the lowering of the oil viscosity and failure of comp mechanical components .

[NZPOMME]

just reading the suggestions. depending on your condensing pressure a 404a system needs to a 45.c condensing temperature otherwise that can start to cause oil problem, and wont give you the oil return that is needed I was made aware of this a while ago but dont fully understand How it all works but I no that my work had issues with something similar that both condensing fans are on fan speed controllers to give it optium head pressure never had a issue since!!

Also is superheat right on both (depends on where you taking you suction pressure as if it a common suction and youve got your gauge on the compressor your not directly reading what each independent exspansion valve is doing)

what are you cooling for it only to have a 10-15 minute defrost?
15minute defrost shouldnt really give you that much of a problem (am taking it a electric defrost) so even L.P switch isnt working your solnoid valve is passing due too that your only pulling 0 psi and also if its brings it down to 0 psi you shouldnt be getting good oil pressure (differntial? depending on your oil switch) which means should of tripped.

as for your oil return what type flow valve or works of head pressure! if youve got a low suction (on pump down) your head pressure wont be that high there for should be trapped in oil sep, is the flow level sticking?

[georgedvf]

just reading the suggestions. depending on your condensing pressure a 404a system needs to a 45.c condensing temperature otherwise that can start to cause oil problem, and wont give you the oil return that is needed I was made aware of this a while ago but dont fully understand How it all works but I no that my work had issues with something similar that both condensing fans are on fan speed controllers to give it optium head pressure never had a issue since!!
I really didn't undestand very well this part, do you say minimum I have to mantain the condensing temperature above 45ºC?


Also is superheat right on both (depends on where you taking you suction pressure as if it a common suction and youve got your gauge on the compressor your not directly reading what each independent exspansion valve is doing)
Yes, we took it right on the evaporators.


what are you cooling for it only to have a 10-15 minute defrost?
15minute defrost shouldnt really give you that much of a problem (am taking it a electric defrost) so even L.P switch isnt working your solnoid valve is passing due too that your only pulling 0 psi and also if its brings it down to 0 psi you shouldnt be getting good oil pressure (differntial? depending on your oil switch) which means should of tripped.
Beef, but there's not much product nor rotation/use of the camera right now, so in 15 min defrost is ended by temperature sensor (time is set to 35min. Electrical defrost).


as for your oil return what type flow valve or works of head pressure! if youve got a low suction (on pump down) your head pressure wont be that high there for should be trapped in oil sep, is the flow level sticking?
We have TRAX-OIL level control.

[sterl]

If you are running only one compressor on a 4-compressor rack and all compressors are pulling off same suction header: you have very low return velocities at least in the header portion....And possibly in each evap circuit during refrigeration. If the rack runs down during defrost and the compressor cuts out on LP, the condenser and oil separator are going to want to head to ambient temperature....depending on how the Oil Separator/Oil Reservoir are pressure controlled and isolated from the condenser (regulator on main discharge or?? Differential or Inlet Pressure only?) the separator could go down in pressure very quickly.

I would check the piping that maintains the receiver pressure. Its very possible with all the other coils pumped out and the receiver still at high pressure the separator is receiving refrigerant from the HP receiver when the compressor shuts down on LP or depending on pressures, the oil is blowing over to the HP receiver from the separator: All via the head pressure control valves. Particularly if the discharge bypass valve is pilot operated, differential pressure type.

[georgedvf]

I would check the piping that maintains the receiver pressure. Its very possible with all the other coils pumped out and the receiver still at high pressure the separator is receiving refrigerant from the HP receiver when the compressor shuts down on LP or depending on pressures, the oil is blowing over to the HP receiver from the separator: All via the head pressure control valves. Particularly if the discharge bypass valve is pilot operated, differential pressure type.
Compressor never shut down due to faulty LP switch.