Strange refrigerant/oil/temp problem

[tim-]

Have you ever been dealing with mach/LS and thinking about modding it? yeah me too.

I have been dealing with both mach1 and ls in the lately and those have caused me some problems.

Well to make a long history short.

When I start modd it I disambled whole unit (in one peace without cutting any pipes) and put it on the side. Mounted the new hardware (condenser, filter, captube, evap flex, suction accumulator, pipes) in the case and brazed everything up and pressuretested it before splitting old unit to mount the compressor. When everything was pressuretested and leakfree (as always ;)) I brazed of the suction + discharge connections from the old unit and brazed the new pipes on. vacuumed the system down below 100microns and then the problems start.

charged the unit and idle with 15/0bar(e) I had -23,5*c evap temp.

damn strange, 22*c outlet of condenser and 9K subcooling and 15/0bar pressure. at those pressures r507 boils at -47*c and evap was only -23.5*c, it should by own experience be something like -42-45*c with same pressure.

i ordered new bottle of refrigrant (thanks LD) same thing again, well little better ~-27.. my old bottle was close to empty so I needed new one anyway, that was the reason I thought it was the refrigerant. A have seen such problems before when bottles is near empty (as this is blended gas, straight gases is never a problem).

As far as i know bad oil can do a little to the temp on evaprator. we all know what bad oil does to the lubrication but that's not relevant in this situation. I was talking with some hvac engineer friends and they didn't have a clue, they just said "proberbly captube blockage or bad gas".

Well I replaced the oil anyway, just to exclude that possibility, vacuumed and charged it with same amount of refrigrant as earlier.

guess what? evap temp with same pressures went down to -43 -44 measured at evap with K-probe.

I did alot of research here on XS about the problem but didn't find a word about this kind of problem. I just wanted to share it with you to let all know what new oil can do if you have problems with temps.

Just wanted to cheer my new experience with you as I guess I'm not the only one who's dealing with those old units... Hope it can helt anyone out there who have problems with their units.

Regards
Tim

[edit]
language.

[killermiller]

Pretty interesting. Thanks for sharing.:)

[PhilippF]

If you get 9K subcooling just after turning it on and no load, my first guess would be air in the system accumulating on the high pressure side and so causing the "subcooling".

Did you charge by weight, so that the complete filling was already in the unit or did you charge just a little and wanted later to add gas to tune the unit?

And did you charge liquid or gaseous refrigerant?

I had a bottle of 507 with some air in it and when I charged gaseous, I also had suddenly 15K subccoling. When charging liquid, it was ok.

But what should this have to do with the oil change? Strange...

[tim-]

well brand new bottle, good vac, 66microns to be specific, I have only open bottle twice, one the first time I charged the unit and second the second time I charged after oilreplacement. bottle went upside down for liquid charge even before I open valve.

I doubt I would have air in refrigrant or the system especially when the refrigrant was brand new and the vac was good (66microns), something strange there anyway.

well, now the unit is running smooth and nice and I have nothing to complain about.. just strange, I replaced the oil and everything was just fine. maybe it was water or something in the oil that freezed in the captube or something, I have absolutly no idea why.. just figure out that new oil was the way to solve the problem.

regards
tim

[PhilippF]

With any kind of blockage (oil/dirt/aliens/whatsoever) the low pressure should have been under 0 bara, so I think this will not be the reason.

[teyber]

http://www.xtremesystems.org/forums/showthread.php?t=165601
You should post url here as well

Interesting!

[kayl]

Was the oil in the unit you had issues with the normal colour.
Only oil I have had issues with was burn oil where you removed the refrigerant gauges and you get loads of white foam. (old rotary compressors that have been running too hot)
Your refrigerant bottle are you sure that it needs to be turned upside down when charging.
Some bottles have a pipe that goes to the bottom of the bottle to ensure liquid charging without needing to tip the bottle upside down.

[jinu117]

That's kind of neat Kayl.
My initial question would be.... how did you measure the vacuum? Did you shut off vaccum pump and let it sit for 10 minutes before checking again? (okay, this is from someone who just spent another gallon of vacuum oil... I seem to go through few of those a month... -_-)