A/C Close Control with Copeland Scrolls.

[Grizzly]

My colleague asked me a question which I could not answer.
I said I would ask the guys on the forum, they may know?

Basically when you need to replace a scroll comp.
Where 1 has failed ( Phase down to earth ).
Can you just change the one.
When they are on the same base plate and linked with a horizontal oil line between them?
How do you determine what the oil levels in each compressor is?
Has anyone just changed one?
And did they add any oil.
In fact, how would you add oil to a sealed system?
Sorry to be so thick.
But it's not my area of expertise!
Cheers Grizzly

[Brian_UK]

I would assume that there is some means of access to the system, Schraeder, back-seat valve, so just pump the oil in.

Or if under vacuum, suck it in.

Checking levels,?? When the oil line is cut would it be possible to get a flex tube into the oil sump to drain out the remaining before a refill?

[Goober]

So.....if I understand right...you have two scroll compressors piped in tandem? common suction? and an oil equalizing line between the two? On an AC unit? correct?

I've just done such an exercise on a two scroll compressor Package AC unit. Wasn't close control though.

I changed one compressor, you have to assume that the oil is level in both compressors, due to the equalizing line. The only way to really change the oil in both comps is to remove both comps and tip them on there side and drain the oil from the suction stub, then either measure the oil removed and replace with same or go to the specs for that compressor and see what the oil charge is. Then prior to welding up the suction stub pour in the oil, or......if you've welded the suction stub or if the compressor can't be removed cut the oil equalizing line and drain oil that way then charge oil in through suction gauge port...Hope this helps

[chemi-cool]

Had to do it once on laser machine water chiller.

As Goober explained, took out both compressors, draind all the oil, put the good one and a new one back, add the missing oil and back to work.

On every compressor name plate you can also see the amount and type of oil.

http://www.hvacrinfo.com/cope_ae_bulletins/TAE1320.PDF

[monkey spanners]

Just an idea, not actually tried, remove oil level plug from new compressor and measure how much come out. Remove duff compressor which would allow oil level to drop to oil level plug level in the two good comps. Fit new comp. Put in three times amount of oil removed from new compressor, plus a bit for the pipe.

There is a special Emkarate oil for these.

[Grizzly]

Thanks so far guys I will come back asap with more info!
Grizzly

[lowcool]

i would even go as far as putting a sightglass in the balance line if possible.oil colour can be an indicator to acid in the system

[El Padre]

Faced the same dilemma before on VRV systems, have always only replaced the faulty compressor and then monitored closely oil return and temperature, and I always check the quantity of oil in the faulty compressor, I think that adding oil can only be done if you know how much is in the entire system, which is unlikely. You will have to pump the oil in as you won't be able to isolate it and use a vac pump, I have always avoided tipping a scroll compressor on its side as I was told that the spring can become unseated, is that true?

Cheers

[SkyWalker]

I was told that the spring can become unseated, is that true?


what spring? i have cut a few scrolls open and never come across one, if anyone knows different im all ears!

[Grizzly]

A Little bit more info!
Apparently these are known as Tandem systems.
There is as I said an oil balance line between the 2 compressors.
There is also a suction pressure balance line between the 2 comps.
Makes sense really as otherwise the
oil would migrate to the compressor with the lowest suction pressure.
Anyway we are going to give the customer the choice of repair!
Basically we have been advised that these are supplied as a pair on one baseplate.
Therefore unless they are replaced as a pair.
There would be no manufacturers warranty.
So we can do the cheaper job by replacing 1 comp but!
There would be no warranty.
Personally as they have quite a few of these.
It would make sense to replace the pair and keep the spare working one this time.
And should any other comp fail
a working pair could be made up.
Grizzly

[al]

Steve

We would also replace both compressors, the old york rooftops came with tandems and were supplied on a single base plate, we tried individual replacement(with clean up driers etc) but kept losing compressors, cheaper to go tandem in the long run.

Al

[Grizzly]

Was that the Old Bristol type?
This isn't a York
Not with Copeland' on it!
It's a Denco Unit.
Cheers Al.
Steve.

[desA]

As I understand these Tandem sets, the compressors are closely matched in performance.

Perhaps swapping in a new compressor could create an imbalance in the tandem set. Is this just a good sales pitch on the compressor manufacturer's part, or an operational reality?

[TRASH101]

Grizzly

I've changed a couple of copelands in tandem arrangement and haven't had any problems yet;)

If you change one then take out the other (its easy cause you will probabley have to cut the suction and oil balance pipes) drain the oil out of both then purge as best you can your condenser(not a prob. usually if it is higher and no traps in pipework) evap and the drier. Add it all up then subtract your new copelands fill weight then charge up to full amount with new oil.

[TRASH101]

Perhaps swapping in a new compressor could create an imbalance in the tandem set. Is this just a good sales pitch on the compressor manufacturer's part, or an operational reality?


Desa

I've found no cause for concern as far as an imbalance in the set. I believe the manufacturers(Denco) just don't want people cutting and brazing the balance lines. They have supplied single comps. before for fitting in tandem systems but I think GEA have took over things now.

[desA]

^ Thanks very much for the wise advice. Much obliged.

[Magoo]

Grizzly
Go back to school. Bob basic shyte and you suck hole this site with a huge rep power and a squillion posts. You must be an electrician with half the knowledge.

[Grizzly]

Grizzly
Go back to school. Bob basic shyte and you suck hole this site with a huge rep power and a squillion posts. You must be an electrician with half the knowledge.

Just shows how little you know then eh!
You sir are out of order!
But fine Have it your way!
Bye
Grizzly

[monkey spanners]

Grizzly
Go back to school. Bob basic shyte and you suck hole this site with a huge rep power and a squillion posts. You must be an electrician with half the knowledge.


That seems a little harsh there Magoo, or is this what passes for pleasant conversation in Auckland :rolleyes:

[Denco Technical]

Hi,

We only supply tandem sets due to the warranty issue with changing only one and having any contaminants failing the compressor, also its very hard to braze on site and we have a special jig for this purpose.

You are welcome to purchase a single compressor but you run the risk and we don't off any warranty on a singular one.#

Thanks Rob
Denco Technical

[aeb200]

Hi,

also its very hard to braze on site and we have a special jig for this purpose.



"Special Jig" -I have usually just tilt compressors on a kerb in the car park when i change these compressors.
It allows keeps oil out of balance line and allows rod to run nicely around joint.

It is a shame the isn't a special jig to get them out of the unit- the common suction line is usually higher than the lip of the fan deck- you have to turn compressors on their side to get them out!!!

[Denco Technical]

"Special Jig" -I have usually just tilt compressors on a kerb in the car park when i change these compressors.
It allows keeps oil out of balance line and allows rod to run nicely around joint.

It is a shame the isn't a special jig to get them out of the unit- the common suction line is usually higher than the lip of the fan deck- you have to turn compressors on their side to get them out!!!

Appologies i stand corrected maybe a pavment outside is suitable enough for the job.

[Brian_UK]

Apologies i stand corrected maybe a pavement outside is suitable enough for the job.
When on site, sometimes you have to make do with what is available.

Site staff do not have the benefit of enclosed, fully fitted workshops.

[airlift123]

That's odd. Here in the U.S. you would rarely come across two scrolls in tandem. In Low temp refrigeration possibly. Ammonia or R-502 systems. A compressor is allways warranted by the serial# no matter even if you only replaced one.

[Rudi Effendi]

I just add and be carefully of rotation electrical system compressor, CW or CCW?