Flood Back After 2 years..

[Mahmoud]

Hellow Fellows...

a 110 cunic meter room @ -30*C for the storage of ice cream.. this room is refrigerated by two systems of a total refrigeration capacity of 6 KW @ Evap. Temp -35*C, the system was running so smoothly from 2 years.. before a week we found one compressor not functioning, we've shift that compressor to our workshop to find it extreamly flooded..!!

i know fellows that there is too many reasons for flood back, i'll mention those which are not the reason :

1- Room Loading: the room is for Baskin Robbins Ice Cream, i.e. there is high loading on the room and frequent door opening.. to the matter of low load condition is no there at all..

2- Suction Accumulator : suction accumulator is there ..

3- Low ambient : the ambient temp. now is 39*C, i.e. no excessive sub-cooling..

the question now, how could 1 of the 2 systems got flooded considering that the 2 systems are running on the same conditions !! with a suction accumulator installed too !!!, why didnt the other fail too ?! if there was a problem in the system .. specially with low temp. application .. it was supposed to be rise in the first week of commisioning ..

i know my posts are all trouble shootings .. i injoy that.. hope there are who share this with me too ;)

The Best ...

[Greg W]

2 years is the life time of a low temp system compressor , with out a sump heater. If you dont have one fitted, liquid can mirgrate back to the sump during off cycle, and if you accumulator is undersized you will flood back on start up. Pipework design, can be a problem , and so can the initial gas charge.
Fit a crank case low temp cut out sensor.
What type of comp was it?

[Mahmoud]

Dear Mark and Greg..

Mark, the compressor's pistons cylinder, crankshaft are weared, the piston is even notheched, and the cylinder now is having the upnormal clearence with the piston, moreover the reeds are broken to hundred pieces.. for the oil, the oil is a little bit under it's optimum level, i know there should be no oil, or little oil at least, but i believe it is flood back indications.. what are trying to say Mark.. please advise..

Greg, actually the contractor did not fit a crankcase heater and i understand this coz it is always hot here ..and the possibilty of flooded start . i dont think so , coz if it was to have flooded start it was to happen in lower ambient throw the 2 years .. the same story for accumulators and initial gas charge ... Greg the type of the compressor is semi-hermetic air cooled..

The best ..

[Greg W]

Well reed valves dont smash them selves up. Liquid does that, Liquid in the crank case washes the oil out of the bearing and cylinders so to speak , So you crank case must be getting cold sometime some how.

[Mahmoud]

Dear Greg.. ofcourse it is a flood back, thats what i explained already man, but i mean i doubt it is flooded start.. we've installed hundreds of units without cch, our climate is too hot man ,, besided it is air cooled compressor Greg..

[Greg W]

Take a suction superheat reading during low load and again at high load, this will answer alot of the questions.

[US Iceman]

HI Mahmoud,

Have you checked the pumpdown cycle to make sure the unit pumped down? If the liquid line solenoid valve is leaking, the evaporator could have been full of refrigerant on start up.

Remember, just because one system does something, does not mean all of them have to do it. We saw something similar to this on the last project. Treat each system separately, and look for the common link if there is one. In the last thread the common link was the client.

Broken valves are usually an indication of liquid slugging. This does not mean the liquid has to be only liquid refrigerant... Oil slugs will do the same thing also.

However, if the system has been running fine for 2 years, oil logging would have appeared before this time has elapsed.

Suction accumulators do not prevent floodback if their internal volume is not sufficient. The only way to prevent a floodback on these small systems is to select the accumulator volume so that it holds more refrigerant than the normal system charge. I have seen these selected using the manufacturers tables and still floodback.

Look forward to seeing how this one turns out.

[Peter_1]

Evaporator completely in ice.
Fans not running while compressor runs for whatever reason.
Suction accumulator sized large enough?

[chillin out]

Hi Mahmoud,


How is oil returned to the crankcase?
I think Marc is probebly on the right track here.
Does the oil seporator have a heater fitted?
Does the comp have an oil regulator?
If so does it work?

And I would fit a crankcase heater wired into the N/C side of the contactor just in case.

Chillin:) :)

[Greg W]

Yeah the defrost fault seems to be high on the list.
What sort of defrost control do you have.

[slrnick]

Also check if heat exchanger in evap isn't split feeding liquid straight back down suction, bypassing txv