understanding scrolls

[devlin maguire]

As I understand it scrolls do not use valves, rather they expose and cover ports, or is it just the dischargre side ? this being the case if it stops with the high side outlet exposed can, when recharging with recovered refrigerant in the liquid phase any oil theat has sank to the bottom of the recovery cylinder flow into the scroll void then on start up try and compress this causing damage I ask as I fell that this has happened as on start and run Iam experiencing what I believe excessive noise I have asked in another post but I did not give it enough of a mention
Devlin

[monkey spanners]

Have a look at this guys vids of a cut open scroll. The generally have discharge check valves built in, so it shouldn't be possible to fill up the scroll with oil from the high side. Is it running the correct way? They are very noisey when running backwards!

http://www.youtube.com/watch?v=E2BcmOetBuw


Jon

[monkey spanners]

Part two,

http://www.youtube.com/watch?v=xuM1V7IgHmM&NR=1

The guy doing the vid is not a fridge engineer so you may want to keep that in mind, they are good vids showing the workings.

[devlin maguire]

Thanks I am sure its connected correctly phase wise as I followed the schemactic on the cover and the low side pulls down, the high side though may not be as the needle is vibrating so much I cant tell as I was reluctant to let it run, I may do phase rotation check tomorrow, it's odd you say that as I had that as my immediate thought, if you have any further ideas I'd welcome them
Devlin

[monkey spanners]

If it sounds a bit like this at the start of the vid then it is probably running backwards.

http://www.youtube.com/watch?v=oaeAx-zRFlM

When they run backwards there is no heat in the discharge line either.
If i fit one and its noisey on start up, the gauges don't move much, (though its difficult to tell in a few seconds) and after i have turned it off the discharge pipe still feels cool to the touch i would swap the phases over, and give it a quick try, another clue is the run current would be low also.
I have not fitted a Maneurope scroll which i seem to remember yours is, i would have a read of any instructions that came with it also, just incase.

Jon

[Grizzly]

Monkey Spanners has described well your options.
I can only say that even the majority of manufacturers.
Just say "you will know by the noise that the comp is making. Whether it is running the correct way or not".

I would suspect not if there is no discharge pressure.
Apparently it is no major issue if you rum one back-wards.
So long as it is not ran for any length of time.
Swapping 2 of the phases will soon indicate whether its running the correct way or not.
Cheers Grizzly

[devlin maguire]

mmm I get heat in the discharge line ok, I wonder if that possible on a manny even if the things going in reverse odd the hs gauge hardly rises
Dev

[devlin maguire]

Saga continues, phase rotation is correct at the compressor terminals, low side pulls into a partial vac, high side gauge stays at 100 psig, but the discharge line gets hot as does the compressor top, I still fell the noise is a issue but maybe I lack experience of thses danfoss/maneuorop scrolls and am getting wound up over nothing, one thing I did notice phases 1&3 draw 6 amp and 2 draws 3.4 (contactor?) I cant find the relevant data on the Danfoss site but I am going to have another look now, voltage is acceptable with a difference of 3 volts over the phases. the oil level is unknown as its either well down or well over a little movement is seen at the sight glass.
Devlin

[philjd26]

Devlin
Did you have to change out the scroll or is this a problem your having with the machine??

Rgrds phil

[devlin maguire]

Phil Hi it,s a change the existing had siezed, there was a great pool of oil below L/S rotolok that emerged from the stuffing gland this I succeded in sorting , when the old one was removed the top of the comp showed signs of heat damage this is a replacement danny/manny
Dev

[philjd26]

Hi dev
What is the application for machine as a matter if interests? I had something similar happen to me, by the sounds of it your either way short or restriction...
In my experience the filter drier had broke assunder and blocked the t e v....

Rgrd phil

[devlin maguire]

phil it's a A/C unit within a AHU for hotel restaurant kitchen and assembly rooms I have changed the filter dryer at the same time I done a acid test on the oil and it came out as ok I recovered the gas R22 and this is going back in I have charged about one third of the gas and its goint upto but not beyond the TEV as far as I can tell I cannot remove the covers from the AHU as its still in use for the heating,I hope to shut the whole lot down on monday and run the comp and add more gas to see i if its getting to the evap any ideas ??

[philjd26]

Dev,
If it failed because of refrigerant shortage, charge to full amount, ie subcool of 10c with a head pressure between 18-20 bar and clear sight glass
If you recovered full amount I would look for head pressure and liquid temp! If the delta between condensing temp and actual liquid temp is excessive I would be suspecting the tev of the cause of previous compressor failure.

Remember scrolls rely alot on the oil returning back if this is not happening you will damage compressor beyond repair in most cases from my experience

[devlin maguire]

So if I take the liquid line temp at the h/s line close to the head and compare that with H/S gauge condensing temp and there is a huge delta T I need to be looking at the TEV ? But if subcooling is within 10 c difference would that not indicate all is well, Oh hold on I think I am with you here if the tev is at fault then gas return will be struggling and therefore oil Am I following you
Dev

[monkey spanners]

Scrolls will also run noisey with a low suction pressure/ low refrigerant charge.

[devlin maguire]

Any clues as why one phase is pulling less than the others 6,6,3.5. amps I understand that current is dependendant on load and the scoll works in a three orbit cycle would a low charge then inticate, that the compression orbit is doing nowt your thoughts guys?

[monkey spanners]

Any clues as why one phase is pulling less than the others 6,6,3.5. amps I understand that current is dependendant on load and the scoll works in a three orbit cycle would a low charge then inticate, that the compression orbit is doing nowt your thoughts guys?

I meant to comment on that but forgot!

First thing if you haven't already done it is to replace the contactor, and any fuses be they rewirable or cartridge type.
The motor should pull near enough the same current on each phase be carefull there are not single phase fans tapped into the compressor feed as this can lead to misleading results. It the three currents are not similar then there is either a fault with the supply, be it main incomming, contactors, switches, fuses or cables, terminals etc, or a fault with the compressor motor itself.
It can be tricky testing voltage on three phase motors as, say a contactor has failed, the motor acts as a transformer and sends voltage back up to the failed component so a quick test shows voltage and its easy to think the part is ok when it isn't, thats why a current measurement is a good idea.

Jon

[devlin maguire]

Jon I had completely forgot about back feed voltage wise, doh! odd because I disconnected motor terminals to check continuity then buttoned them back up to check voltage I even remebered to take my isulated testing block with me I will be replacing the contactor,MCB's and the main isolator this week
Cheers Dev

[devlin maguire]

Hi all well after a long wait the client eventually got a new contactor which I have fitted, some time next week I will be back at this, so if its still rattling I intend to charge it with what I have taken out However if it still rattles is there a posibilty of a faulty unit the suppliers are not to forth coming with advice,any final thoughts guys
Dev