Oil Temperature in Compressor

[georgedvf]

Hello!

In a Parallel Compressors Rack with R-404A and polyolester oil, is there a range of temperature that the oil should be at???? Is the temperature measured at the sight glass of the compressor???

I've heard that it must be hot enough to be sure there's no liquid refrigerant on it, and not too hot to loose its properties. Is that right?

Thanks in advanced!

Regards!

[chillerman2006]

when the system is not running the compressor needs to be kept above the condensing temperature/pressure of the refrigerant in use to prevent the refrigerant from migrating to the compressor

both oil and refrigerant have an upper limit for temperature and when exceeded will begin to break down their molecular composition and there fore they should always be kept within their design spec

you will need the data sheet for the exact oil used to check its designed temperature range

for refrigerant you can see this on a pressure enthalpy chart

[georgedvf]

Thanks chillerman2006.

Do you know where can I find a Bitzer Oil properties sheet?? I can't find it.

So if there is low temperature when the compressor is running it couldn't mean there's liquid refrigerant??

Thanks!

[chillerman2006]

Bitzer is the compressor manufacter not the oil, if you can find the sheet for the compressor it should list the oil

I would not worry about it though as the higher limit for the oil will exceed the refrigerant higher limit and the lower limit will be much lower than the condensing temperature/pressure of the refrigerant

if the crankcase heater is working the oil will be warm enough and will not be able to overheat the oil

[georgedvf]

Mmm... in the bottle says "BITZER BSE-32". It doesn't mention any other manufacturer.

[Magoo]

Mr Google says it is a poly sythetic oil, with the designation of 32 suggest that is the viscosity rating, possible low temp oil. Keep sump oil temp between 45 and 50 'C.

[chillerman2006]

Mmm... in the bottle says "BITZER BSE-32". It doesn't mention any other manufacturer.

Then thats JUST RE-BADGED... Bitzer do not have an oil refinery...

[georgedvf]

Thank you both!

Mr Google says it is a poly sythetic oil, with the designation of 32 suggest that is the viscosity rating, possible low temp oil. Keep sump oil temp between 45 and 50 'C.

Magoo, any particulary reason for those temperatures???

[Magoo]

Hi Georgedv,
keeping sump oil temp high is to stop refrigerant being absorbed into oil during off cycle. Stops oil foaming and being carried over and into system

[georgedvf]

Ok, but what about the running time?? what temperature should I be looking for?? I'm still looking for the particular oil properties sheet but just to understand well:
1.-not too high so it will break its molecular composition;
2.-not too low to condensate refrigerant (when running this would be very very low so practically will be imposible right?)

Thanks!

[Gary]

Ok, but what about the running time?? what temperature should I be looking for?? I'm still looking for the particular oil properties sheet but just to understand well:
1.-not too high so it will break its molecular composition;
2.-not too low to condensate refrigerant (when running this would be very very low so practically will be imposible right?)

Thanks!

Most compressor manufacturers want an upper limit of no more than 225F on the discharge line 6 inches from the compressor in order to avoid cooking the oil... but that's not the hottest point in the system. The hottest point is inside the compressor at the discharge valves. This runs about 50F higher than the discharge line. IOW, the upper limit for the oil is about 275F.

On the off cycle, refrigerant will migrate to and condense in the coldest part of the system. This is usually the evaporator, but not always. If the evaporator is warmer than the outdoor temp, the compressor crankcase can become the coldest point. The purpose of the crankcase heater is to make sure the crankcase is never the coldest point. IOW, the oil needs to be warmer than the evaporator.

As I understand it, the temperature in crankcase heaven is about 160F... but it can vary a lot in either direction.