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Old 05-07-2017, 10:42   #1
kcj
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Frigoboat freezer do-loop

Help me, Please....

I have a frigoboat freezer cabinet connected to a danfoss twin 2000 compressor, stock install on my circa 2003 lagoon 470. I am now on my fourth iteration of the following: system works fine for 2-4 months, system suddenly stops working due to trip of low pressure sensor, gauges read negative on suction side, +70 psi on high side. remedy is to vacuum system for 1-4 hours (while trying to heat cabinet and components to 100degrees), and refill system with no additive r134a. Then it works fine for 2-4 months. Before recharging the system holds constant pressure for at least an hour, suggesting no leaks.

What is causing this cycle? Remedies?

More specifics: the twin 2000 is water cooled, with two danfoss 50f compressors and an oil cooler in between. i am told this model was never offered in the US (its a Lagoon cat...). there is a filter dryer, then a sight glass, as well as a TEV.

When it works it works like a champ, but these cycles wreck havoc on cruising provisions and bounties of the sea...

Thanks in advance for your insights!
Cheers,
John
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Old 05-07-2017, 10:55   #2
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Frigoboat freezer do-loop

I does sound like you have a leak in the system . Using a vacuum to check for a leak is not the way to go , there is not enough pressure . You need to find a tech that can pressurize your system with nitrogen to approximately 200 psi and then let it stand with a gauge on it . If there is a leak you will find it this way . Use the old soap and water trick on every joint flare nut and brazing point . Fix it , evacuate it and charge it . Good to go .

Just make sure you find a tech that knows what he is doing with nitrogen , there's a lot of pressure in this bottles and he could damage the system and you if he is not careful .


Regards John
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Old 05-07-2017, 13:24   #3
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Re: Frigoboat freezer do-loop

CEM,

Thanks for insight!

Who knew leaks can take that long to "mature". can you leak test the cabinet evaporator independent of the "whole system"?

Now to find a tech with nitrogen knowledge...

cheers
John
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Old 05-07-2017, 13:57   #4
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Re: Frigoboat freezer do-loop

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Originally Posted by kcj View Post
CEM,

Thanks for insight!

Who knew leaks can take that long to "mature". can you leak test the cabinet evaporator independent of the "whole system"?

Now to find a tech with nitrogen knowledge...

cheers
John

Testing the evaporator alone can be a challenge but possible . You have to separate it from the system usually at the couplers and then attach it to a another coupler with a schrader valve and pressurize the plate.

Slow leaks are hard to find but not impossible , just takes time.

This is a little information about the different ways .

https://www.epa.gov/sites/production...eakTesting.pdf

Regards John.
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Old 05-07-2017, 20:11   #5
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Re: Frigoboat freezer do-loop

In order for the system to reach a vacuum, it sure sounds like a potential blockage problem. Since it develops over time, it sounds like water forming in the system and then freezing and blocking. You indicate a vacuum down, BUT to what micron level is the system being vacuumed down to and for how long? Sub 200micron would be my recommendation and to have it held there over night to allow time for the water to get out of the oil.
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Old 06-07-2017, 12:54   #6
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Re: Frigoboat freezer do-loop

Kcj, Reoccurring low pressure could be caused by loss of refrigerant or restricted refrigerant flow. Vacuuming and recharging appears to have not been sufficient or it just masked original problem. Connecting two BD 50 compressors together is risky do to controlling oil level and compressor cooling. Water cooling is another problem. You reported a sight glass, low pressure cutoff switch and a TXV. Is there also a high pressure cut off switch? When one of these systems is equipped with a TXV refrigerant flow control there must also be a receiver to hold excess refrigerant when freezer is at operating temperatures.

Question Is there a Refrigerant Leak?

Are you reporting high pressure of 70 psi with compressor running? This would indicate low on refrigerant. Preferred Pressure after 15 minutes running would be 95 to 120 psi depending on Seawater temperature. Best performance for compressor temperature cooling is 105 to 115 psi high pressure.

System pressure with compressor off is of little value on this type system do to its ability to store excess liquid refrigerant.

Vacuum tests on capillary flow control systems can show some results in 12 hours with a slow loss of refrigerant say one ounce per month. Once to two ounces per month would produce the refrigerant losses you might have if high pressures running was 70 psi.

Question Is there a refrigerant flow problem?

Refrigerant restrictions to flow are not common but do happen on TXV system caused by moisture freezing in TXV orifice or solid material blocking valve inlet screen. Because you report a liquid line sight glass there will be a moisture indication inside sight glass, If not there is a simple test to check moisture freezing in TXV control valves.
Run system until low pressure is in a vacuum. Now place wet hot rag over TXV. If there is moisture freezing in TXV wet rag will temporally freeze to valve and you will hear refrigerant moving. A minute or so later rage will fall free of valve and refrigerant flow will stop again. Low pressure will also follow the freezing and thawing of moisture. Another sign of moisture freezing and melting in TXV is evaporator will be covered with 33 degree F condensation

About the only other time a inlet screen on TXV will clog is if solid material from filter gets into line leading to TXV. Because system’s refrigerant flow is not restricted all the time solid restriction is not likely in your case.

Recommendation

I would add refrigerant if running high pressure is less than 105 psi. Now if after 15 minutes low pressure is in a vacuum. Follow my TXV freeze test. If it is confirmed to be moisture in System a Deep dehydration process is require. Some say you cannot get moisture out of systems with Ester oil it can be done but it is easy.
If system operated normally with correct high pressure you need to develop plans for finding the refrigerant leak. Because this is a Frigoboat system it probably has sliding O ring seals in line connections, these are reported by others to leak over time. I would order correct O rings and replace them before vacuuming system again..

If you can find some one with a electronic leak detector you can test the evaporator for leaks. Best method to test for evaporator leaks is when box is warm and closed for 12 hours. The pressure in evaporator will now be at its highest pressure box interior will be charged with refrigerant if there is a leak. Zero leak detector before opening box. Without touching anything in the box lower detector inside to sample hopefully air without refrigerant fumes. This test will only tell if there is a leak inside box It will not find the small two month refrigerant loss you are looking for. If evaporator is leaking it needs to be replaced.

If you have not detected or confirmed a refrigerant leak there is a possibility of a micro size hole in seawater condenser. Some manufacturers units have experienced these failures where low voltage current discharge overboard allows water to mix with refrigerant. The test for refrigerant leaks in condenser is to remove water hoses from condenser and replace with deflated balloons. If the flat balloon opens at all after 12 hours the condenser must be replaced. Only one out of three of these failures can be saved without replacing the complete system.
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Old 07-07-2017, 15:48   #7
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Re: Frigoboat freezer do-loop

Thanks to all for the ideas!

re vacuum: the first time we ran the vacuum overnite, most recently only for an hour. IIRC the vacuum got to -28psi on the suction side (just above pegged), the high side pegged at zero. when the vacuum was shut down and the gauges closed vacuum pressures did not change for an hour.

re charging: i charge the system with a combination of viewing the sight glass and monitoring the frost lines in the box. most recently the system, when warm, was filled to apprx 8psi on the suction side--which resulted in a high pressure of about 120psi (i need to confirm this...). the sight glass shows a slow stream of bubbles and the evaporator frosts on all sides and the freezer is making ice. when the system ran for 3 days the suction side was down to 2 psi and the TEV had nearly 1/2" of frost on it. the twin compressors (and pump) were drawing about 11 amps.

Why the heavy frost on TEV?

i will try the TEV hot rag test in the AM, as well as search for some balloons.. i do not have an electronic leak detector and the unit is a front loader so i'm not sure that will work as described... may try to pressure test the system, some how.. its easy to track down a nitrogen tank, but the regulators are expensive and no one rents them. sounds like i have a deep evacuation in my future

thanks again to all.. more to follow
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Old 08-07-2017, 07:28   #8
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Re: Frigoboat freezer do-loop

Forget the idea of dehydration until you have confirmed that there is moisture in your system by non destructive measures like I suggested. Yes, call a tech person and he will always take the approach that is most profitable for him. You know it takes 2 to 4 months before low pressure to drop into a vacuum.

Test to find proof there is moisture in refrigerant

Add refrigerant to bring refrigerant pressures up to near normal and no higher. After running for 20 minutes do not tamper any more with refrigerant volume.

With thermostat set at your normal setting run system as long as it takes to verify there is moisture in system by :
• No frost on evaporator only very cold condensation.
• Hissing Sound in evaporator stops and restarts again in several minutes. Place a hot rag on expansion valve to shorten the freeze and break loose thaw of ice in valve. If there is a low pressure gauge connected it will display the freeze and thaw process by showing positive pressure and a vacuum as ice melts and thaws.

I hope this info will help you rule in or out the question of moisture in refrigerant. It you do have moisture in refrigerant it would be a major problem to remove it.
Hopefully your solution is more likely a typical Frigoboat connector O ring leak.

Frost on TXV can be normal or it can also show reduced refrigerant high pressure flow indicating low refrigerant volume in system.
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Old 09-07-2017, 13:15   #9
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Re: Frigoboat freezer do-loop

weekend update!

visited system on Sat am--system had run overnite and high side was only at 70 psi (it was never at 120 as previously represented...). i added refrigerant to get high side to 110. This raised suction to 12 psi. ran system for a few hours. One time suction pressure dropped to 2psi and i put a hairdryer (no hot rag available) on the TEV and the pressure then appeared to stabilize at 9.0/100 psi and drawing 8 amps. box was making ice and had frost on all surfaces.

Sun am--system operating normally. suction side now at 10psi and high side dropped to 80, and still drawing 8 amps.

TEV always frosts. do I correctly understand this mean its NOT a moisture problem???

Are bubbles in the sight glass indicative of anything?

Am i correct that this suggests a leak and it should be pressure tested with a focus on o-ring joints??? if so i am in search of nitrogen to do a leak test....



many thanks!
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Old 09-07-2017, 13:34   #10
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Re: Frigoboat freezer do-loop

If your TXV frosts up , then you are getting refrigerant flow which is good . Where is your Sight glass located? If it is close to the TXV it should have no bubbles in it at box temperature or close to box temperature . If it does then you are more then likley low on refrigerant . Does it have a moisture indicator in it ? I still strongly think that you have a slow leak in the system.

If you any flare nut connections, you could check them and make sure nothing has come lose.

The next thing would be to pressurize the system and start looking for that very small leak , also as Richard has said , frigoboat couplers are notorious for leaking , usually at 5 year intervals and require an O ring replacement .

Regards John
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Old 09-07-2017, 13:42   #11
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Re: Frigoboat freezer do-loop

If you have bubbles....you could be low on refrigerant.

Did you charge the system to a full charge by Volume because trying to charge a TXV system by pressure won't get you there.

Here's a little basic review of charge troubleshooting on a TXV compressor/Holding plate system.

Harbor Freight makes a good Refrigerant leak sniffer for $49 or you always have the old trusty bubble test approach.

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Old 09-07-2017, 17:32   #12
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Re: Frigoboat freezer do-loop

thanks to all for the responses! Much to keep me awake at nite...

i am now on a mission to procure a nitrogen tank and regulator to do a pressured leak test. opting for the soap and water approach

the sight glass is between the filter dryer and the TEV. it has always had bubbles, even when I KNOW it was over filled--ie there was frost on the return side. Does this suggest a leak as well???? any indication of where??

My concern in doing a leak test the frigoboat twin2000 compressor alone has SIX fittings to test (in, out, suction port, HP port, suction sensor and HP sensor) as well as a fair amount of plumbing between the two compressors and the oil cooler. would the sniffer be a reliable tool in that situation?? in addition there are three more sets of fittings to test. I'd gladly replace the twin2000 beast if i knew it would solve the problem.

It will be a few days before i get back to the boat.. thanks again

Cheers,
john
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Old 09-07-2017, 17:36   #13
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Re: Frigoboat freezer do-loop

Quote:
Originally Posted by kcj View Post
thanks to all for the responses! Much to keep me awake at nite...

i am now on a mission to procure a nitrogen tank and regulator to do a pressured leak test. opting for the soap and water approach

the sight glass is between the filter dryer and the TEV. it has always had bubbles, even when I KNOW it was over filled--ie there was frost on the return side. Does this suggest a leak as well???? any indication of where??

My concern in doing a leak test the frigoboat twin2000 compressor alone has SIX fittings to test (in, out, suction port, HP port, suction sensor and HP sensor) as well as a fair amount of plumbing between the two compressors and the oil cooler. would the sniffer be a reliable tool in that situation?? in addition there are three more sets of fittings to test. I'd gladly replace the twin2000 beast if i knew it would solve the problem.

It will be a few days before i get back to the boat.. thanks again

Cheers,
john
Ah but frost may NOT be an indicator of a system that is overcharged if the TXV has been messed with or is not working properly. It can flood the plate with refrigerant even if undercharged frost the line up all the way back to the compressor.

I would spend the $49 money on a sniffer or get out a refrigeration tech that has one or you will be chasing your tail.

A Big Question is...What is the correct amount of refrigerant Charge called for in the system by the manufacturer because if you could find that out and then add that correct amount THEN you could rule out charge as an issue and then look at other possibilities. Right now it could be Charge of the TXV....we know not witch.
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Old 01-08-2017, 05:32   #14
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Re: Frigoboat freezer do-loop

thanks again to all for the insights!

sorry for the delay, i have been distracted closing our now ex-homestead....

replaced all the QD orings and had a pro pressure test with nitrogen after a vacuum. there was a slight leak per the gauges, consistent with a slow leak, but found no bubbles. But there was a questionable suction line found---two rubber flex hoses at the ends of hard copper pipe and with corroded connections. they suspected a weeping leak thru the rubber hose, and no way to see it. Soooo we are in the process of replacing this with a copper line and repeating the pressure test. if that fails then off to pressure testing evap and raw water heat exchanger.

more to follow
Best
John
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