Charging Scrolls

[Fridgy Dave]

Why is it recommended that Scrolls not be valour charged even when on R22. ?

[Grizzly]

Why is it recommended that Scrolls not be valour charged even when on R22. ?

Er! You got me there Dave. That's a new one on me?
That statement does not make sence.
Grizzly

[Fridgy Dave]

I meant vapour charged and I read it in a suppliers book about Copeland scrolls and wondered why that was the recommendation

[desA]

I see no problem with an initial charge into the liquid line, prior to starting the compressor. Once the system is running, vapour can safely be discharged into the suction line - slowly does it.

Just be jolly careful that the system is running at low pressure when you open up the feed line & please triple check that you are feeding into the suction line.

It could be nasty if you're trying to feed into the high-pressure side (by mistake), if the gas bottle is at all dodgy. Can cause serious injury, or death.

I always nip straws when topping up on the fly.

[DEVIL]

As Grizzly stated
never heard something like that, it would be recommended to charge vapor if you can (for r22), then you are for shore there is no liquid flowing to the compressor.
But some times i charge the full charge in the liquid line, so there you get to the problem, of "liquid or vapor", because if you charge vapor you can never charge the full charge, because the vapor will go fast to the equal pressure and vapor is light not heavy, and that might be the statement in the book

[VRVIII]

I meant vapour charged and I read it in a suppliers book about Copeland scrolls and wondered why that was the recommendation

Hi,

Compressor manufactures may recommend different charging methods as the compressor design can be completely different even though they employ the same scroll type principle. (Low press shell/High press shell/Radial compliance/Full compliance/Discharge or suction valves/etc etc).

I think Copeland scrolls use a low press shell with a full compliance scroll and no discharge valve, these are allowed to back spin briefly as pressures equalise when unit stops. The most common reason for scroll compressor failure is overheating due to excessively high compression ratios or high suction superheat or a combination of both.

Example for A/C application using Copeland scroll:
If you consider charging an a/c system from vac and you manage to add 50% of the total charge into liquid line then start the unit, suction press will be very low and the head press will continue to increase (especially if a fan speed controller is fitted). Resulting in excessively high compression ratio and SSH.
Charging vapour into a suction Schrader connection will not be enough to prevent overheating but can be enough to prevent LP switch from tripping, operating under these conditions can damage the compressor within 2~5 minutes (scroll tips worn/thrust face damage/bearing damage).

The best way to charge the unit would be to add the complete charge amount into the liquid line from vac, try heating the refrigerant bottle with hot water to increase the press. If required and you have at least 80% of charge added you could start the unit then liquid charge into the suction line providing this is done sensibly.

I’m sure Copeland also recommend that you,
Never close the suction valve
Never pump down into a vac or use comp to pull oil into system
Never bypass compressor motor protection

No arguments Devil

[lawrence1]

Fridgy Dave,
Scrolls will go out on internal thermal overload if return vapour temps are high.You need to bomb charge the system first or if adding refrigerant charge using liquid refrigerant and do it quickly.
Regards

[VRVIII]

Fridgy Dave,
Scrolls will go out on internal thermal overload if return vapour temps are high.You need to bomb charge the system first or if adding refrigerant charge using liquid refrigerant and do it quickly.
Regards

This depends on the scroll compressor type, never bomb charge the suction line or liquid charge a high press shell/low press dome scroll compressor. Unless you want to be changing it again.




This can result in compressor damage which isn’t always apparent:

• Scroll can be fractured/broken - in some cases the compressor will be down to earth due to broken fragment falling into windings.
• The discharge reed valve can be damaged/weakened - Results in compressor over heating and premature failure.
• Oil can be lifted/pumped out of compressor at start up.
• Liquid refrigerant can also wash oil from top bearing – Results in damage to hardened face of bearing and eventually compressor will seize.

[Fridgy Dave]

I would always charge a system in vac through the liquid line always and probably get about 70-80% of the charge in there then vapour charge the rest and have never had a problem. I am also aware that scrolls handle flood back better than any other comp design and I have installed 2 racks with scrolls with vapour injection and I just thought it strange that someone would suggest liquid charging when the comp was running after being charged prodominently through the liquid line rather than vapour charging.

[VRVIII]

I would always charge a system in vac through the liquid line always and probably get about 70-80% of the charge in there then vapour charge the rest and have never had a problem. I am also aware that scrolls handle flood back better than any other comp design and I have installed 2 racks with scrolls with vapour injection and I just thought it strange that someone would suggest liquid charging when the comp was running after being charged prodominently through the liquid line rather than vapour charging.

Hi Dave,

The compressor in question was a full compliance scroll which will allow slight lateral & vertical movement of the orbiting scroll and has no discharge reed valve. Therefore the risk of compressor damage due to liquid pumping is reduced and within reason they are better at handling liquid.

However I would always recommend following/obtaining the correct charging method form the manufacturer as the compressor technology is continually advancing along with required service methods . It’s not a case of the same procedure applies to all scroll compressors or applications .

[desA]

What is bomb charging?

[VRVIII]

What is bomb charging?

Hi Desa,

Basically forcing liquid into a system as fast as you can get it in, fine for liquid line but not so good for suction side.

[desA]

^ Thanks VRVIII.

That would worry me a lot. I like to leave a system time to settle a while, even after filling through the liquid line. I've always been a little concerned about thermal shocks on the equipment & the high-side being over-full of liquid.

[Grizzly]

^ Thanks VRVIII.

That would worry me a lot. I like to leave a system time to settle a while, even after filling through the liquid line. I've always been a little concerned about thermal shocks on the equipment & the high-side being over-full of liquid.

Good Point about thermal shock desA.
Basically for those of us that have seen the damage that indiscriminate charging of Liquid can cause.
Particularly on Shell and tube evaps or condensers.
I always charge with vapour (If a blend - regulate liquid through a cracked valve. Forcing the liquid to flash off whilst entering the system).
Once the system pressure has reached the equivalent 0c pressure.
You can charge with liquid into the Hp side, without fear of causing Ice crystals around your tubes.
Which can crush the tubes.
And yes it does happen!
Especially if you are charging without the chilled water Pumps on.

In the long run it is simpler to vapour charge initially.

Back to your dillema
Read the attached and it may explain the confusion?
Cheers Grizzly

[VRVIII]

Good Point about thermal shock desA.
Basically for those of us that have seen the damage that indiscriminate charging of Liquid can cause.
Particularly on Shell and tube evaps or condensers.
I always charge with vapour (If a blend - regulate liquid through a cracked valve. Forcing the liquid to flash off whilst entering the system).
Once the system pressure has reached the equivalent 0c pressure.
You can charge with liquid into the Hp side, without fear of causing Ice crystals around your tubes.
Which can crush the tubes.
And yes it does happen!
Especially if you are charging without the chilled water Pumps on.

In the long run it is simpler to vapour charge initially.

Back to your dillema
Read the attached and it may explain the confusion?
Cheers Grizzly

Hi Grizzly,

All valid points for chilled water application, but the example I was referring to was standard heat pump split or package unit using the current Copeland scroll compressor(s).
Also see screen grab from copeland site regarding current compressor for this application.
Copeland scn gb.pdf

[Grizzly]

Hi Grizzly,

All valid points for chilled water application, but the example I was referring to was standard heat pump split or package unit using the current Copeland scroll compressor(s).

I totally Agree VRVIII.
Sorry I rushed the above reply and didn't manage to attach the reference I was making.
The below is direct From Copeland's Heatpump tech docs.
which may of been the cause of Fridgy Dave's dilemma?
What do you think?
cheers Grizzly

35 System Charging Procedure

Rapid charging on only the suction side of a single-phase Scroll equipped system or condensing unit can occasionally
result in a temporary no-start condition for the compressor. The reason for this is that if the flanks of the spirals
happen to be in a sealed position, rapid pressurization of the low side without opposing high side pressure can cause
the spirals to seal axially. As a result, until the pressures eventually equalize, the spirals can be held tightly together,
preventing rotation. The best way to avoid this situation is to charge on both the high and the low side simultaneously
at a rate which does not result in axial loading of the spirals. The maximum charging rate can be determined through

simple tests.

[VRVIII]

I totally Agree VRVIII.
Sorry I rushed the above reply and didn't manage to attach the reference I was making.
The below is direct From Copeland's Heatpump tech docs.
which may of been the cause of Fridgy Dave's dilemma?
What do you think?
cheers Grizzly

35 System Charging Procedure
Rapid charging on only the suction side of a single-phase Scroll equipped system or condensing unit can occasionally
result in a temporary no-start condition for the compressor. The reason for this is that if the flanks of the spirals
happen to be in a sealed position, rapid pressurization of the low side without opposing high side pressure can cause
the spirals to seal axially. As a result, until the pressures eventually equalize, the spirals can be held tightly together,
preventing rotation. The best way to avoid this situation is to charge on both the high and the low side simultaneously
at a rate which does not result in axial loading of the spirals. The maximum charging rate can be determined through

simple tests.

Hello Grizzly,

The Copeland sheet you attached makes perfect sense as most of there comps incorporate ASTP (advanced scroll temp protection), but would think this is a general manual and may even be for previous scroll models (see my previous post attachment). However I was relating to the a/c manufactures recommendations, obviously the charging procedure may vary depending on the refrigerant circuit.

Rapid charging on only the suction side of a single-phase Scroll equipped system or condensing unit can occasionally result in a temporary no-start condition for the compressor

Example: Adding refrigerant into liquid line would pass through to suction side equalizing the pressure when a capillary or TEV is used in the circuit.

As I said in previous above post

However I would always recommend following/obtaining the correct charging method form the manufacturer as the compressor technology is continually advancing along with required service methods . It’s not a case of the same procedure applies to all scroll compressors or applications

Regards,

VRVIII

[Grizzly]

Thank You for persevering with correcting my ignorance VRVIII.
Basically the below is taken from Copeland's website Doc dated 09-09.
As you state Liquid on both sides of the system.
Fridgy Dave had a point after all!
A good one at that!
Thanks guys for re- educating an old git like me.
Grizzly.
Quote:-

5.4 Charging procedure
CAUTION

Low suction pressure operation! Compressor Damage!

Do not operate

with a restricted suction. Do not operate with the low-pressure cut-out
bridged. Do not operate compressor without enough system charge to
maintain at least 0.5 bar suction pressure. Allowing pressure to drop below
0.5 bar for more than a few seconds may overheat scrolls and cause early
drive bearing damage.
The system should be liquid-charged through the liquid-receiver shut-off valve or through a valve
in the liquid line. The use of a filter drier in the charging line is highly recommended. Because
R410A and R407C are blends and scrolls have discharge check valves, systems should be
liquid-charged on both the high and low sides simultaneously to ensure a positive refrigerant
pressure is present in the compressor before it runs. The majority of the charge should be
placed in the high side of the system to prevent bearing washout during first-time start on the
assembly line.

[Fridgy Dave]

Thanks for the info guys dont work on alot of a/c units and mostly work on hermetic and screw compressors so not exactly an expert on scrolls

[VRVIII]

Thank You for persevering with correcting my ignorance VRVIII.
Basically the below is taken from Copeland's website Doc dated 09-09.
As you state Liquid on both sides of the system.
Fridgy Dave had a point after all!
A good one at that!
Thanks guys for re- educating an old git like me.
Grizzly.
Quote:-

5.4 Charging procedure
CAUTION

Low suction pressure operation! Compressor Damage!

Do not operate

with a restricted suction. Do not operate with the low-pressure cut-out

bridged. Do not operate compressor without enough system charge to

maintain at least 0.5 bar suction pressure. Allowing pressure to drop below
0.5 bar for more than a few seconds may overheat scrolls and cause early
drive bearing damage.
The system should be liquid-charged through the liquid-receiver shut-off valve or through a valve
in the liquid line. The use of a filter drier in the charging line is highly recommended. Because
R410A and R407C are blends and scrolls have discharge check valves, systems should be
liquid-charged on both the high and low sides simultaneously to ensure a positive refrigerant
pressure is present in the compressor before it runs. The majority of the charge should be
placed in the high side of the system to prevent bearing washout during first-time start on the
assembly line.

Hi Grizzly,

There’s nothing wrong with a bit of friendly banter thanks for locating correct detail from Copeland documentation. I only found this out while carrying out works on an a/c system with this type of Copeland scroll
Another thing I found out is that the compressor has an internal high to low bypass safety, this is a bi metal disk that will open if scrolls overheat. The bypass would then cause a rapid increase in discharge and motor temp causing the motor protection to trip. The bi metal disk should reset prior to the motor protection device. However I suspect the reaction time isn’t quick enough when the compressor is started with very low suction pressure (very high compression ratio).

[Grizzly]

Hi Grizzly,

There’s nothing wrong with a bit of friendly banter thanks for locating correct detail from Copeland documentation. I only found this out while carrying out works on an a/c system with this type of Copeland scroll
Another thing I found out is that the compressor has an internal high to low bypass safety, this is a bi metal disk that will open if scrolls overheat. The bypass would then cause a rapid increase in discharge and motor temp causing the motor protection to trip. The bi metal disk should reset prior to the motor protection device. However I suspect the reaction time isn’t quick enough when the compressor is started with very low suction pressure (very high compression ratio).

Yes I read that myself VRVIII.
I would of posted the whole document.
But Forum restrictions prevail!
The larger Maneurope have something similar.
Many people have been caught out with them.
If anyone would like some of the afore mentioned Literature.
Follow the link below-
http://www.emersonclimate.eu/documen...tdocid=1&sub=1

Cheers Grizzly

[DEVIL]

I think that it is indicated to charge liquid in the suction is because if you would charge vapor at the first moments of start the compressor would take all the refrigerant (being vapor it wouldn't be a lot) and push it in the liquid line and this way getting under the 0.5 bar limit.

But i don't think after the start that it would be a problem to vapor charge the rest (for R 22).

Actually if all the safety devices are in function i don't think you would get in trouble any way

[powell]

Here's a link to Copeland's AE bulletins.

Section 4-1312 is a good place to start.

http://www.hvacrinfo.com/ae_index.htm

[VRVIII]

Here's a link to Copeland's AE bulletins.

Section 4-1312 is a good place to start.

http://www.hvacrinfo.com/ae_index.htm

Hi Powel,

Thanks for the link but bulletin 4-1312 is dated Jan 2005 and has no relevance with current 2009 range of Copeland Scroll Compressors for Air Conditioning (ZR18K* to ZR380K* & ZP24K* to ZP485K*)

However the info is still very useful for working on previous models