kollmann-marine.com

[mholmes]

I installed a BD50 w/AEO module, air-cooled condenser, large evaporator plate system (parts from RParts) about 6 months ago, in a 9cu.ft. icebox with 4in of blueboard insulation (also rebuilt). I pressure tested it before charging: it held 150lbs of pressure for 3 days without noticeable change.

As of three days ago it was staying cold just fine; three months ago I measured the duty cycle to be 20% (to maintain icebox temp ~36degreesF in an ambient 60degree environment, lightly filled with foodstuffs). I hadn't paid close attention since I measured the duty cycle, but I have a green LED next to the icebox to tell me the compressor is running, and the red fault LED also in eyesight. The compressor seemed to be running a normal amount for the past few weeks, and there was no action on the red LED.

The past two days I had the icebox turned off so I could install shelving for organization. I turned it back on last night and the compressor ran 12 straight hours to get the fridge down to temperature (from 60F to 38F)--there is not much food in the icebox either.

Only 1/8th of the evaporator plate frosted over (and stayed that way for the duration of the 12 hours the compressor ran). It appears to be the first 1/8th of the tubing after the capillary tube.

Could I have damaged the evaporator plate during my construction project? Could this be a symptom of a damaged plate? Or perhaps I did not notice the condition before the past few days, and my recent project drew attention to it?

If it weren't for the construction project, I would suspect insufficient refrigerant, caused by a slow leak somewhere, which I did not find during my installation. But wouldn't I have noticed that last week (before my project)? Would the green LED have been on all the time (it definitely wasn't running more than 50% of the time).

boy I really REALLY hope I didn't damage the plate. I tried to be so extremely careful. I will be really depressed if that ends up being the problem.

thanks,
matt
syzygy v40 #201
www.syzygysailing.com

[kollmann]

One area I like to remind people of is that if capillary tube system is serviced with a warm ambient temperature and then operated at a low ambient cooling medium performance will be degraded and frost area will be reduced. I do not believe that reduction of 80% frost area in this case is causing your problem.

A very slow leak in low pressure side of system would have been detected 6 months agowith the three day test. The question now is the loss of refrigerant a micro leak developed over time or was it a new leak do to a very small hole caused by working on box’s interior.

Sometimes leaks are caused by not using special refrigerant flare nuts. Light weight hardware store nuts tend to expend at a different rate as temperature changes causing leaks. Many times failure to use servicing fitting caps with a seal inside can cause small leaks. If refrigerant loss was slow over time when in operation evaporator frost coverage would slowly be reduced beginning with a small area. I have seen frosted area reduced to 50% in six weeks and when system is off a few days all refrigerant is lost. When system is not running the low pressure side of system is the same as high side.

If evaporator prior to the three day shelf work had frost covering 90% of its surface and now is only 20% I would suspect you damaged evaporator plate.

The only recommendation I can give you is to add refrigerant in small amounts till frost covers 80 to 90% of evaporator. Then stop compressor and test for leaks at all connections with a mixture of 50/50 liquid soap and water. It is important to use a one inch paint brush against test area forcing mixture into a shave cream texture. This method of leak testing is slow one fitting at a time but it will find leaks as small as ½ a ounce a year. Leaks in aluminum evaporators are very hard to find and are not repairable. If you drilled any new mounting holes in evaporator I would check them first. Again pressure in low side of system when unit is running will be less than 8 psi so leak testing is best done with system off.

[mholmes]

WOW am I glad you exist on the internet, thank you so much for the advice.

That is great to know, that leaks in the low pressure side can be masked until the system is shut down entirely--makes complete sense but I had never thought of it.

Is it possible that there is nothing wrong at all? I charged the system when it was about 70deg ambient; now it is about 45deg ambient. Could that alone account for the reduction in frost pattern from 100% to 20%? You may have been saying not, when you wrote "I do not believe that reduction of 80% frost area in this case is causing your problem" but I am confused about what you meant by that statement.

So I will charge the system with UV dye refrigerant and then look for leaks.

If it loses its charge rapidly, then I will have strong evidence that a hole in the evaporator plate is the culprit. Additionally, if the leak is that large I should be able to see the UV dye with the blacklight, I assume. If after two days it is still running strong, with no evident signs of leaks with the blacklight, then I have good evidence that the leak was a long slow one, and I will test each fitting with the soap/water mixture.

About the UV dye: are the cans available at the autoparts store, pre-loaded with the dye, ok to use? I saw the previous post in which you gave an amount of dye per amount of refrigerant, but I don't know how to add the dye to the system if it doesn't already come in the can of refrigerant. Can the dye identify small leaks? Do you personally use the UV dye to troubleshoot?

I have your book; it convinced me of the futility of attempting to repair any holes in the evap. plate, so if that is the culprit I will replace it.

If there is a slow leak, over time it draws in moisture that contaminates the system, correct? So it can probably be recharged a few times, but in the end moisture will be sucked in through the hole in the low side and clog the capillary tube, at which point a full "reboot" (leak repair, vaccumed to remove moisture, filter/drier replaced) will need to happen anyway, right? Any sense of how long it takes for the moisture to contaminate the system through a slow leak?

Additional data & responses to your comments:

1) When I first built the system I DID have a slow leak (this was determined because it did not hold the 150psi for a few days, it lost a little bit). I tightened up the two flare fittings joining the tubing run to the refrigeration fittings at the compressor, then retested and it held the pressure. If there is a micro-leak in the system, I would speculate that one of these flare fittings would be the culprit, probably the flare fitting on the low pressure side from what you wrote. You said that the pressure test should have identified this leak, though, so I will keep it as a suspect hypothesis.

2) Unfortunately, and to my immense annoyance, I cannot recall what the duty cycle or frost pattern was prior to messing around in the icebox two days ago. I know that it wasn't 100% duty cycle just from vaguely paying attention to the compressor running, but I have no information beyond that. I rack my memory for clues, without success.

3) I used all refrigeration flare fittings from RParts in the system construction (it was their 1M kit).

4) I used a gauge set with good o-ring seals to originally charge it.

apologies for the length of this post

again, a million thanks for your expert input
matt

[kollmann]

Refrigerant charge on a system using a capillary tube flow control device must be correct or performance is will be degraded. As the condenser’s cooling medium, in your case air, changes temperature the pressure and temperature of refrigerant leaving condenser will upset the equilibrium for the liquid and vapor passing through capillary tube. Factory charged refrigerators are generally charged with a fixed volume of refrigerant by weight based on standard day cooling medium temperatures. When these small cap tube systems are field serviced on a boat in the north to correct evaporator superheat and then transit south to the tropics evaporator super heat will be low causing frost to extend beyond evaporator. In you case going from warm to cold condenser cooling medium would reduce the frost area on evaporator. I dough that initial low refrigerant is the only cause of your problem, so add refrigerant and leak test.

Florissant dye and a black light is the best way to locate leak areas. To enhance the dye I also use special glasses. For these small units I recommend 10 to 20 drops of dye. The 4 ounce cans of refrigerant and UV dye contain ¼ ounce of dye and a mixture of oil and refrigerant and are intended for systems containing 2 to 5 pounds of refrigerant, this may be too much oil and dye for your system. I warn about too much dye because car manufactures say too much dye in their systems cause compressor problems. Do not mistake the regular non UV dye cans also sold to detect leaks. It is a good idea to test areas first before adding dye as there are materials that under black light will glow the same as dye. The material tie wraps are made of will glow. After finding a leak area with dye I follow up with the soap test to further pinpoint leak. The best results with black light will be in a dark boat.

[mholmes]

super. one more thing--perhaps I am overlooking an obvious answer, but how does one add just a few drops of UV dye to an already charged system?
thanks,
matt

[kollmann]

To insert dye you must solve two problems first: Find some of the Florissant dye and acquire a ¼ to ¼ flare brass union to screw into end of blue servicing hose so that dye can inter hose. Do not add more than 20 drops of dye.

Dye can be added to blue hose of servicing gauge set. Begin with both red and blue gauge valves closed. Connect refrigerant bottle to yellow hose. With blue hose held vertical open blue valve and purge refrigerant through gauge set out through blue hose, then close blue valve. Refrigerant is heaver than air so keep blue hose vertical while adding dye. Connect blue hose to low pressure side of compressor. Turn refrigerant bottle upside down so that liquid refrigerant will flush dye into system. Open blue valve for 5 seconds then close valve and turn refrigerant bottle with gas only side up. Wait several minutes before starting compressor so that liquid refrigerant will have returned to gas in compressor. Service with refrigerant adding small amounts and then wait till low pressure stabilizes before adding more. Run system a few days to mix dye with oil. If evaporator stays covered with frost then turn compressor off for three days. When frost line on evaporator no longer covers 90% of evaporator use black light to find leak.

[mholmes]

should I add any oil while I'm doing this?

-I now have a small container of the UV dye (in a plastic bottle with screw-top cap, unpressurized).
-I have the yellow glasses and a small penlight (really very cool to look at everything with that setup, I have to say).
-I have a 1/4-1/4 flare brass union.

To confirm: So I put the flare union on the end of the blue hose (the end that attaches to the service fitting), hold it vertical in my hand, and purge it. I continue to hold it vertical to prevent air from entering, and then I add 15 drops of the UV dye into the flare union, letting it drain down into the hose. Then I remove the flare union, and gently move the end of the blue service hose down to screw it onto the service fitting--this would be when I am most worried about air slipping into the system, as I am moving the hose and screwing it onto the horizontal service fitting. I leave the service fitting closed to the gauge set while doing this.

Then I hold the refrigerant can above the level of the gauge set, and invert it. (blue valve closed). Liquid refrigerant piles up against the blue valve. Then I open the blue valve for five seconds and then close it. Liquid refrigerant piles up against the service fitting. Then I open the service fitting and the liquid refrigerant enters the system, flushing the dye out of the hose and into the system with it. Then I wait a few minutes for all the liquid refrigerant to boil off in the system (thereby avoiding liquid slugging of the compressor).

Then I start the compressor and service with additional refrigerant as necessary to obtain a 100% frost pattern on the evaporator.

Then I put everything away and wait until it is apparent that some refrigerant must be leaking away, however many days or weeks that may take, and it will be evidenced by a diminished frost pattern on the evaporator.

Then I take out my glasses and blacklight and go searching.

Did I get all that right? And the minute amount of air that slips into the hose as I'm screwing it onto the service fitting is acceptable, I'm supposing, since this is how you're saying it is supposed to be done.

this is pretty cool stuff. And I'm pretty excited that I'm learning how to do it all myself.

as always, many thanks,
matt

[kollmann]

Matt, you are on the right track. When adding liquid refrigerant the bottle does not need to be higher than gauge set just upside down.
After removing ¼ union I put my finger over end of hose until connection to unit is made. You may want to use a syringe needle to add dye to hose as gas bubbles will be coming out as oil goes in.
Once hose is connected open three way suction servicing valve halfway then open blue gauge valve for five seconds. With both valves open at the same time liquid will flow into unit taking dye with it.

[mholmes]

Ok, I hooked up the gauge set to check the operating pressures, before doing anything else, and when I saw that the suction side was pulling somewhat of a vacuum, I decided to modify the plan.

I was thinking that there was potential for air (maybe moisture) to have entered the system if the leak was on the suction side. Also, when I went to the refrigeration supply they were having a sale on a vacuum pump, so I bought it.

Then I borrowed a guy's micron vacuum gauge from down the dock, and vacuumed down to 450 microns, and closed off the system. Within 20 minutes it had risen to 520 microns, confirming a leak. So I let the system equalize with ambient pressure, then added 15 drops of UV dye to the gauge set suction side hose, into the end with the male-male flare union as you described. Then I vacuumed down the system to 450 microns and charged with refrigerant. Now I am waiting for leak to present itself.

I have doubts that the amount of UV dye will be successful in identifying the leak: I overcharged very slightly at first, and bled off a tiny amount of refrigerant from the connection at the flare fitting. Only then did I realize my mistake: I probably released UV dye onto the area, reducing my ability to identify the leak. So I put on the glasses and looked around with the light and couldn't see anything at all. This causes me to doubt the effectiveness of it showing a leak. Though perhaps after it runs for a few days the dye will have mixed better with the refrigerant.

The dye seems to dry/stick to surfaces, though, so perhaps most of the dye ended up painting the inside of the blue hose on my gauge set, and very little made it into the system. I don't know, and for now I'm not going to stress out about it. We depart for mexico in two weeks, and for now my icebox is cold and my food is unspoiled. I have a vacuum pump, a couple of extra filter/driers, and a greatly improved understanding of my problem, so I'm confident that I can deal with whatever wherever, even down in mexico or the south pacific this summer (fingers crossed!) if I have to. If the dye doesn't show the leak, I'll test each fitting with the soap/water method, which I now understand was probably the most thorough approach to have taken in the first place (which I should have known from your book and advice, but was naively looking for a shortcut).

Thank you very much for your excellent advice and patient explanations. Your book has been very helpful to me in gaining an intuition about the various specialized problems that may arise in our small boat systems, and the corresponding approaches to fixing said problems. Above and beyond the book, this forum and your responses to my questions have tripled my refrigeration knowledge (albeit not very large to begin with!), and it brings me happiness to be able to learn and understand how to take care of these things for myself. You have my gratitude!

regards,
matt

[kollmann]

A 30 micron change in 20 minutes I would believe is normal as trapped liquid is being phase changed to gas. When 12,000 microns of vacuum is equal to one inch of gauge indicated vacuum a 30 micron change does not prove there is a leak. If system was vacuumed for four hours with system’s ambient temperature of at least 100 degrees F and vacuum reduced to 5,000 microns in 20 minutes then somewhere something is leaking and it may even be the servicing gauge set or its hoses.

Ten drops of dye is sufficient for your system. The leak you have if there is one is a micro size leak and will not display visible dye for many days with system running or when frost area coverage of evaporator is reduced by 50%.