Causes of pressure release valve activating

[danielbeek]

Hi all, hoping for some insight in to a weird problem.
I have a fridge/freezer of 80L on my boat, driven by a York (CCI) 210 compressor on the engine. System is about 7 years old, and previously worked well. The condenser is a meter away from the compressor, and is made up of two 60cm water cooled heat exchanger pipes followed by a larger diameter 60cm pipe with the pressure release valve on it.
I had it recharged the other day after I rebuilt the compressor with a new shaft seal and valve plate gaskets. The old shaft seal was leaking excessive oil, and the replacement passed pressure testing and stopped all leaking.
Unit was charged with R406 and mineral oil (as before), as well as fitting a new dryer and transfer valve.

I ran the system for an hour and a half the day after re-gassing, but on my second use a week later the system ran for only a couple of minutes before the pressure release valve (mechanical, not solder plug) opened and dumped out most of the seriously expensive gas....
The condenser is definitely getting plenty of cooling water, so overheating alone is not the culprit.
What else can cause this to happen?

[Brian_UK]

What sort of vacuum level did you achieve before you recharged the system?

I assume that the system used R406 previously.

[passandscore]

Is the system equipped with a high pressure cutout switch? If so I would inspect it as it should have shutdown the compressor! If you do not have a cutout switch I would consider installing one before you run it again because like you said, refrigerant is costly!

Possible reasons for a relief to open (Assuming you do not have a high pressure cutout switch):
1) Non condensables due to poor vacuum after recent repairs
2) Faulty relief valve. Hansen had a recent recall.
3) Valve not sized properly
4) Condenser has little or no water flow.
5) Isolation valves not open fully.

[danielbeek]

Hi Brian,
no idea about vacuum reached - I recall seeing the test gauge(s) in vacuum, but not knowing what it should be pulled down to I did not take much notice and left it to the technician.
Yes, system was previously charged with R406.

[danielbeek]

Hi,
There's no compressor cutout switch unfortunately.
When you say, 'valve not sized properly' do you mean the pressure release valve, or the transfer valve? The transfer valve was replaced by technician who said something about the last being blocked. System still worked prior to compressor rebuild... The RV is the original item, and was not touched.

[danielbeek]

Hi, is it true the shaft seal will fail if the sump of the compressor was not filled with oil? I understand it's a carbon seal, lubricated by splashed sump oil? I saw the system charged with oil via the vacuum line, but not poured in to the sump via the plug. It seems this would explain why it worked fine the first time, and passed pressure/vacuum testing.

[nike123]

If water flow is OK, than it could be heavy fouling of algae inside condenser (water side) which affect heat transfer from refrigerant to sea water.


Measuring of condenser TD and Approach will reveal that. TD should be <10K and Approach <5K

Anyhow, correctly adjusted high pressure cut-out switch shall prevent this to happen again.

[cateyes]

I agree with previous posters that a HP cutout switch should be installed and set below threshold of RV. Be aware that RV'S setting could have changed after blowing down just once, I've seen this to the point they could leak by during what appears to be normal parameters/operation. Just a heads up... What were your head pressures during first operation and second operation. You could have developed fouling in a weeks time sitting idle if your water flows are normal as you pointed out. Gauges shed a lot of light on the big picture when troubleshooting a case like this. There could be other issues as a few others have already pointed out. Please keep us posted on what you find.

[passandscore]

Hi,
There's no compressor cutout switch unfortunately.
When you say, 'valve not sized properly' do you mean the pressure release valve, or the transfer valve? The transfer valve was replaced by technician who said something about the last being blocked. System still worked prior to compressor rebuild... The RV is the original item, and was not touched.

When a relief valve is not sized properly its setting in normally lower then that of the high pressure cutout control and will open before the control has had time to shut the compressor down. This scenario is irrelevant seeing as you have no HP cutout.

I agree with cateyes, you could have developed fouling in a weeks time sitting idle. Once a relief lifts I always replace it! I would replace the relief, install a high pressure control cutout, evacuate to 500 microns, recharge and monitor the operation with gauges attached. At this point you should be able to troubleshoot the problem more thoroughly.

[sedgy]

get the tec, back and tell him he has a problem , or have you payed him all ready ?( cash ) get him back ( job under warranty) regards = sedgy