Coopeland Scrol not pumping

[fridgability]

Hi all
Perhapps some of you may be able to throw some light on a problem that I encounterd yesterday.

I attended a shop display fridge with a Coopeland Scroll compressor, approx 2HP single phase 240v.

When I arrived the compressor was running but no cooling was taking place at the evaporator. The discharge pipe was cool and the suction pipe was at ambient. I connected a suction gauge and found that the pressure was very high probably about 8 bar. ( the system is on R22). the compressor body was warm to hot(ish). All this gave me the the impression that it had failed internaly.

I switched it off and back on almost immediatly and to my surprise it began to operate normally. The discharge pipe got hot, the suction cool, the suct pressure fell to about 2.5 bar and the temprature in the display fell rapidly. I switched it on and off several more times but all remained well.

Could the compressor have been running backwards and if so why? There are two capacitors, presumably start and run, could one of these be faulty?:confused:

Any thoughts on the subject would be most welcone

[GXMPLX]

Faulty capacitors cannot make the compressor run backwards. Direction of rotation is fixed by the design of the start winding.

Though reverse rotation is possible in scrolls if you get sudden short outages and power resumes while the scroll is expanding the compressed gas it had, modern small Copeland scrolls have an Anti Rotation Cam that should prevent reverse rotation.

Using the model of the compressor I'd search for a protection that it might have that needed a reset.

Sorry this is little but at least I'm 99.99% sure the capacitors are not to blame!

[GXMPLX]

On second thought if dirt had come in between the scrolls they would not compress.

Maybe what you did forced reverse rotation that blowed the dirt out when you resumend power it started compressing again.

This a fairies are also possible!

[WINJA]

copeland scrolls have a bimetalic relief dome between the suction and disharge . its internal and if tripped the compressor usually needs to cool down for 1 hour or so before it resets.
and yes i would check the capacitors there is a small chance with psc/csr that it can start in either direction if faulty, but usually it just sits there and hums

[fridgey]

As mentioned by WINJA the bimetalic dome is there as protection device. If there is prolonged operation at high discharge temperatures the bimetalic relief dome pops open venting the discharge into the suction. This subsequently disengages the scroll but the compressor motor stays running unloaded until the compressor cools, then in re-engages automatically.
So it seems like there is another problem with your display fridge, possibly short of gas or faulty TEV. You didn't mention what refrigerant?

Cheers

[GXMPLX]

copeland scrolls have a bimetalic relief dome between the suction and disharge . its internal and if tripped the compressor usually needs to cool down for 1 hour or so before it resets.
and yes i would check the capacitors there is a small chance with psc/csr that it can start in either direction if faulty, but usually it just sits there and hums

I disagree with you and fridgey.

Earlier models that had this would trip the thermal protector of the motor because the discharge was directed to it.

Modern scrolls don't do this because they just release the pressure of the floating seal and do not bypass discharge to suction.

If motor was running the bymetal would not reset by just turning of the power off and back on. It simply would not cool enough.

I can confirm this if fridgability mentions the model and serial number of the compressor (to check manufacturing date).

[monkey spanners]

My money would be on a short power cut and the power came back on as the compressor was spinning backwards and it kept going that way.
It would be worth testing the capacitors to see if their uf rating is still within the 5% or 10% tolerance and changing if they are not.
It is also worth fitting a time delay of a minute or so in the control ciruit just before the contactor coil connection, to stop this being able to happen.
Something else to check is the differential on the LP switch sometimes if its set too low or has gone out of adjustment they can cut out on LP and be running backwards as the LP switch cuts back in and they stay running that way.

Cheers Jon

[coolhibby1875]

if a scroll wheather it single or 3 phase runs the wrong way you would know about it as it would be jumping about the unit and making one almighty noise i think the scroll has just been diengaged due to faulty start capacitor

[GXMPLX]

My money would be on a short power cut and the power came back on as the compressor was spinning backwards and it kept going that way.
It would be worth testing the capacitors to see if their uf rating is still within the 5% or 10% tolerance and changing if they are not.
It is also worth fitting a time delay of a minute or so in the control ciruit just before the contactor coil connection, to stop this being able to happen.
Something else to check is the differential on the LP switch sometimes if its set too low or has gone out of adjustment they can cut out on LP and be running backwards as the LP switch cuts back in and they stay running that way.

Cheers Jon

Hmm ... you could be right if it were a 20 year old compressor ... I think I'll take that bet!

[fridgability]

Thanks all for your thoughts on the subject, I did check the refrigerant charge (R22), the sight glass cleared quite soon so I think its not short of gas. Ill check the capacitors and LP switch as recomended. I let you all know how I get on. Many thanks again.

[WINJA]

I disagree with you and fridgey.

Earlier models that had this would trip the thermal protector of the motor because the discharge was directed to it.

Modern scrolls don't do this because they just release the pressure of the floating seal and do not bypass discharge to suction.

If motor was running the bymetal would not reset by just turning of the power off and back on. It simply would not cool enough.

I can confirm this if fridgability mentions the model and serial number of the compressor (to check manufacturing date).
Came across a brand new one just last week with the bimetal dome open ,the compressor was running and no pumping the LP was set to low it had no suction cooling and the dome opened, just left the CFM running to cool it down with the compressor disconected , it cooled down within hour or so , then tested it and corrected the LP settings .
It would possibly have been cycling on klixon before i got there

[fridgey]

Originally Posted by GXMPLX http://www.refrigeration-engineer.com/forums/images/VA_RE/buttons/viewpost.gif (http://www.refrigeration-engineer.com/forums/showthread.php?p=111159#post111159)
I disagree with you and fridgey.

Earlier models that had this would trip the thermal protector of the motor because the discharge was directed to it.

Modern scrolls don't do this because they just release the pressure of the floating seal and do not bypass discharge to suction.

If motor was running the bymetal would not reset by just turning of the power off and back on. It simply would not cool enough.



What I've said above is correct, bar the fact that it auto reset itself. The compressor does have to be turned off too cool. I was going from memory and it's been a while since i've come across the situation. Anyway, Copeland calls the system Advanced Scroll Temperature Protection.

See this: http://http://www.emersonclimate.com/contractor/pdf/astp_overview.pdf


It's not on all copeland scrolls, but i have come across this problem a couple of times. The cause of the compressor disengaging in both instances was a system related problem.
Was the system was short of refrigerant
Was due to the system having poor suction superheat, due to a system design issue.
In both case it was not a fault of the compressor.

Cheers

[GXMPLX]

Came across a brand new one just last week with the bimetal dome open ,the compressor was running and no pumping the LP was set to low it had no suction cooling and the dome opened, just left the CFM running to cool it down with the compressor disconected , it cooled down within hour or so , then tested it and corrected the LP settings .
It would possibly have been cycling on klixon before i got there

I said I don't agree, not that I hold the flame of truth!

Give me the model and if it is a small one like fridgability mentioned maybe the serial number too and we'll start a new thread on this one!

[GXMPLX]

What I've said above is correct, bar the fact that it auto reset itself. The compressor does have to be turned off too cool. I was going from memory and it's been a while since i've come across the situation. Anyway, Copeland calls the system Advanced Scroll Temperature Protection.

See this: http://http://www.emersonclimate.com/contractor/pdf/astp_overview.pdf



It's not on all copeland scrolls, but i have come across this problem a couple of times. The cause of the compressor disengaging in both instances was a system related problem.
Was the system was short of refrigerant
Was due to the system having poor suction superheat, due to a system design issue.
In both case it was not a fault of the compressor.

Cheers

Me too with old compressors.

ASTP does not seem to be the problem here because it was a short turn off and back on. No way ASTP wold have reset here, that´s why everibody should start mentioning model numbers and if there are several generations of that model, the serial number too.

Things change.

Please read what I posted to Winja before.

Antir Rotation Cam won't let the scrols run backwards continuously.

It is possible that if a compressor has run backwards for long time to wear the ARC, (or maybe dirt don't let it break) but I think the probability of this happening is far less than blowing dirt back to the crankase. It would fail on lubrication though this could depend on system design and oil level in the crankcase when it all started ... In my opinion of course!

[WINJA]

I said I don't agree, not that I hold the flame of truth!

Give me the model and if it is a small one like fridgability mentioned maybe the serial number too and we'll start a new thread on this one!
nah . you go look for the serial number , its friday and im off to burger king:)

[Larry2]

I had a similar experience on my system. On A/C mode, it had worked all summer. Then one morning it stopped. The suction line was warm and the compressor case was hot and switched off on the thermal. When it cooled, it ran okay again and had a cool compressor and cool suction lines. The compressor case (ZR47K3) cooled, it ran for another day or two before posing another cut-off on thermal.

I watched the system start and run for a cycle. Around 30 seconds into start-up, the contactor studdered. The compressor ran backwards after that and the compressor case went from cool to hot.

I replaced the well worn contactor. The system ran the rest of the season without incident.

It is mentioned in the Emerson application notes that power disruptions can cause a single phase scroll to kick backwards momentarily and continue running that way. A well pitted contactor is one chance for that to happen. I should mention the current draw was about right. I didn't hook up gauges. It didn't seem necessary.

[Below 0]

Found a unit recently with scroll running and suction and discharge pressures equal. Shut the unit down and while i was thinking about what the cause was i noticed a sticker on the side of the compressor. It stated that when overheated the compressor will continue to run but not pump. When compressor cooled it ran normally , in the end it was a blocked expansion valve that caused the compressor to overheat. I researched this and found that a metalic strip lifts the scrolls apart when hot thus still runs but does not pump. They are now using this technology in conjunction with solenoid valves to load and unload compressors.

[chillyblue]

I've noticed with scrolls on systems that pumpdown, they seem to release pressure (make a swishing noise/clashing noise) when the low pressure gets close to zero, the pressure rises and then pulls down again, this repeats untill it finally cut-out, is this normal?????

CB

[littleyapper]

this is a common fault .. it's to do with the floating plate on the scrolls .. check that the sroll is not pumping down belos 7psi .. below this it's possible that the scrolls will seperate and lift the floating plate ... once that plate resets then it will work away as normal

[Si@airconworld]

I used to work on loads of Mcquay stuff and they all had Copeland scrolls - Believe you me they will certainly run backwards.

I found that when the scroll stops the equalisation of refrigerant pushed the scroll backwards momentarily, and if you resupplied power at that precise point it would keep running backwards

Faulty cheap ****ty contactors caused this all the time.

[Tiesse]

I've seen this before & the time I saw it was on an air con unit with a compressor that an ex colleague had changed. I got called in as the compressor was overheating & then not pumping.

My ex-colleague had managed to fracture the TEV phial capillary when lifting the compressor into position & whilst after cooling down & starting, the sightglass was clear, the noise that the compressor was making made it clear that the system was pumping down. I put my gauges on & sure enough, the TEV was knackered.

No cooling coming back to the compressor meant it was overheating & the protection device caused it to stop pumping (despite continuing to run).

From memory, there is a sticker on the compressor body advising you of this protection.

[Tiesse]

They are now using this technology in conjunction with solenoid valves to load and unload compressors.

Digital scroll capacity control

[paddymurray]

i have encountered this problem some several times before i reckon the valves can stick in the head on the compressor i think it must be dirt in the system that does it