Problem with oil returns using R508B

[Staniel]

Hello guys,
first I want to say hello to all people from here. I have a problem with a ultra freezer. We changed the compressor for low freezer with a new one. we filled with R508B and now we have some problems with oil returns. I read on this site about a solution: to add some Pentane. But nobody says how much :). Maybe some one can tell me this thing and what method he use to do this.
Thank you and sorry if I say some old already things.

[mbc]

could you give more information about:
compressor model
room temperature
oil type you used
describe your system.
might I can help you.

[Staniel]

Hello, the model is AEZ2411Z, the temperature of the room is around 16-18 Celsius, the type of the oil is the one from the compressor, I didn't put extra oil but when I changed the old compressor with the new one I didn't take off the entire old oil. The system is a ultra freezer in cascade from GFL Germany.
I wait your help . Have a nice day

[mbc]

ecumseh AEZ 2411 Z , hermetic compressor, LBP 220/240V -R404A - R507 -R407B -
Displacement : 7.6 cm³
Net weight : 10.2 Kg
Oil charge : 250 cm³
Oil type : P.O.E /
Expansion device : Capillaire/Détendeur
Capillary/Exp° valve
Cooling :Forced
Windings resistances at 20° C
Main Winding : 6.8 Ohms
aux. / Auxiliary Winding : 30.2 Ohms
Intensité / Current
nom. / Rated current RLA : 2 A
max. / Max current : 3.1 A
dém. / Start current LRA : 13 A
Ap. Electrique / Electrical equipment : CSIR
Protecteur / Overload : MRP56AMK
Temporisation / Time Check : 7.5s - 14s / 9.4 A
T° ouverture / Opening temp.: 105° C
fermeture / Closing temp. : 61° C
Option / optional : T0599
Relais Intensité / Current relay : MTRP0027
enclenchement / Pick up : 6,2A
déclenchement / Drop out : 5,25A

these information i got from internet .
you see it works with P.O.E oils and your old compressor might works with mineral oils.

2) I wonder , how you find the oil is not return to you compressor.

[Staniel]

Hello, thank you for your answer.
First i want to say that I use this equipment for -85 Celsius, and now my lowest temperature is around -60 Celsius. This is the reason that I think my oil is not returning.
Best regards

[D.D.KORANNE]

Use of a microfibre oil separator is suggested ....arrest the oil going forward rather than worry about bringing it back from evaporator. Besides the suction gas velocity at -60 deg c v/s -85 deg c could also play part due to suction pipe diameter.

Dd koranne

[Staniel]

Use of a microfibre oil separator is suggested ....arrest the oil going forward raither than worry about bringing it back from evaporator. Besides the suction gas velocity at -60 deg c v/s -85 deg c could also play part due to suction pipe diameter.

Dd koranne

hello Koranne, thank you for your advice.
The part with the microfiber oil separator is very nice, I will try this.
About the second part of your message, I don't understand very well what you mean. Maybe you can say more explicit about that?
Thank you

[coolman]

If you only reach -60, than indeed oil in the evaporator may be part of the problem.
standard poe oil has a viscosity of 32 meaninf that T - 60 or lower it will be thick like sirup, in combination with the very low gasflow at these temperature oil return will become a problem.
In r508b datasheet there is a recomendation to ad mineral oil to ad in increased oil return.

on the other hand charge in these systems is very critical.
you should take readings in suction pressure, and superheat of suction line straight after evaporator, and make sure it it within the range to reach -80 or lower.

[Staniel]

If you only reach -60, than indeed oil in the evaporator may be part of the problem.
standard poe oil has a viscosity of 32 meaninf that T - 60 or lower it will be thick like sirup, in combination with the very low gasflow at these temperature oil return will become a problem.
In r508b datasheet there is a recomendation to ad mineral oil to ad in increased oil return.

on the other hand charge in these systems is very critical.
you should take readings in suction pressure, and superheat of suction line straight after evaporator, and make sure it it within the range to reach -80 or lower.
Hello,
Thank you for being agree with me about the oil return problem. Do you know something about th ePentane solution? How to fill with this and how much? Or do you have other advice about solve this?

[coolman]

as stated in the documentation R508b adding mineral oil can have a possitive effect on oil return.
same happens with R438b a drop in for r22, here we add about 30% of mineral oil ie gs3, in ypur case it contains 250cc so ad about 70 cc mineral oil.

that is if there is a oil buildup in evaporator.
do your reading suction pressure/superheat discharge/pressure/temp/sub cooling support these findings

if there is oil buildup, you should end up with low superheat and low discharge.

[LowTemp-10F]

When you change the low stage compressor, did you change the oil separator and flush the system?