Correct amount of refrigerant in a capillary tube boat refrigerator system

[Richard Kollmann]

What method do you use when adding additional refrigerant to a capillary tube refrigeration system? Then how do you know later refrigerant charge is correct for best performance?

When moving boat from a warm climate to a cold climate with a capillary tube system will it require more or less refrigerant in refrigeration system?

What are the problems with the use of blended refrigerants in our boat refrigerators?

[Bill O]

Originally Posted by Richard Kollmann

What method do you use when adding additional refrigerant to a capillary tube refrigeration system? Then how do you know later refrigerant charge is correct for best performance?

When moving boat from a warm climate to a cold climate with a capillary tube system will it require more or less refrigerant in refrigeration system?

What are the problems with the use of blended refrigerants in our boat refrigerators?

OK I'll be the first to bite from what I've found out w/our fridgoboat system for our 6 cu ft. refrigerator.

Had to add a slight amount of charge when we initially set up the system as it seemed a little low during warm weather. (no frost on evap.)

We have an amp meter inline to measure the amp draw, Ah, etc. and look at current draw in combination w/the amount of frost on the evap. plate. Only add small amounts of refrigeration to the system then let it stabilize before adding more. Too much refrigeration would be when we see a high current draw on compressor and the exit tube is frosting up after it exits the box. (not seen this yet).

The amount of frost on the evap. plate is how we measure performance and how the compressor is running. Our system was set up for warmer temps and with season changes/temps lower, we need to turn the mechanical thermostat up to get the compressor to run correctly. Based on our observation, would think more refrigerant would be needed in colder clims. for the system to run better.

[billknny]

If a significant part of the evaporator is unfrosted after running for a few minutes, it is short of refrigerant. Add a little, and wait at least 10 or 15 minutes to let everything equilibrate. If the frost line still isn't covering almost all the evaporator, add a bit more. Repeat.

To do it right can be a long project; tedious with lots of waiting. One of the reasons so few professionals actually get it right. Time is very expensive, and few clients want to pay for an hour of sitting and waiting.

If there is a faster way, that is sure to get it right, I don't know it.

I haven't seen a change in performance based on ambient conditions, but that isn't entirely fair, since I live aboard, and migrate with the seasons so "room temperature" in the cabin doesn't change that much.

[Coolerking]

Is this a test?
Not sure I understand why you would start a thread asking questions that you already know the answer to, but ill bite...
If this is a mass produced pre engineered system, then that # has already been figured out for you and will never change.
Read the label on the unit.
Start from scratch and leak check, evacuate and weigh the correct charge into it and observe for frostback.
Fractionalisation?
I might be mistaken, but I dont know of any mass produced marine captube systems that use blended refrigerant. Usually those use a TXV.
134a/r12 is it for cap tubes.
Once its correct, leave it alone, no charge adjustment for climate or anything else should be made.
Thats what the tstat is for.
Ok...flame on...ill be waiting..

[Richard Kollmann]

Correct amount of refrigerant in a capillary tube boat refrigerator system

1. What method do you use when adding additional refrigerant to a capillary tube refrigeration system? Then how do you know later refrigerant charge is correct for best performance?

Bill O, an billknny, are not far off for doing it yourself refrigerant servicing as long as they follow it up a day or two later with monitoring frost line and then amperage comparison provided by compressor manufacturer based on compressor speed. It is always better to be slightly low on refrigerant than having added load of too much refrigerant. Twenty five grams too much refrigerant wastes energy. Fifteen grams low on refrigerant may cause compressor to run slightly longer but will have little affect on energy loss.

Coolerking’s comment on refrigerant servicing is great but of little value to a boater without a way to measure grams of refrigerant. The small job shops that put together ice box conversion systems do not label the volume of refrigerant needed for each or their condenser/evaporator systems like Adler Barbour does. Besides if there is some refrigerant in system why remove it just to determine how much to add.

Adler Barbour thirty years ago sent out to their twenty four service agencies a refrigerant service bulletin for adjusting correct refrigerant level in these small units. I still use their procedure beginning with a completely warm system. Start compressor and wait ten minutes for pump down to be completed, then add refrigerant till amperage is stabilized at correct amperage for compressor’s preset speed. Refrigerant volume can only be adjusted in the time window between 10 and 20 minutes after start up. Five amps on the BD2 and up to the BD3 fixed speed compressors would be the correct refrigerant charge. There are procedures on my web site for servicing these cap tube systems.


Small 12/24 volt compressors with thin plate roll bond evaporators almost always use Capillary Tube refrigerant flow control devices. Large energy storing evaporator plates control heat absorption more efficiently with Therno Expansion Valves (TXV) devices. Fixed orifice capillary tubes are used on small refrigeration systems because they are cheap, and do not require a refrigerant receiver. A disadvantage of cap tube is the fixed orifice, which causes the flow rate to be inflexible. Another problem is that changes in evaporator load or head pressure can result in poor efficiency do to over or under feeding evaporator. In sizing the capillary tube it is difficult to calculate the diameter and length accurately. Sense the capillary tube needs to match the Btu capacity and desired operating temperature range capillary tubes generally are matched to evaporator capacity operating temperature ranges. Capillary tubes generally are matched to evaporator capacity operating temperature ranges -10 to +5 F Freezer and +5 to +20 refrigerator evaporator temperature.

The true benefit of TXV’s over Capillary tubes is valves with a + 40 to -40 degrees F are used to insure rapped temperature pull down with greater efficiency a must for energy storing in larger boxes.

[RaymondR]

Hi Richard,

I changed my boat refrigerator over to a hydrocarbon based refrigerant called Hychill Minus 30 about 18 months age and it is still performing well on it.

I just changed a small portable fridge which had R134 in it to the Hychill. I vacced it down for a couple of hours first and then slowly introduced the Hychill holding about 15 psi on the low side until it rose to 20 psi. By then the return line was icing to the compressor (it has an anti sweating cover all the way back to the compressor which makes it impossible to see until it gets to the compressor) then bled a small amount off. I then wound the thermostat right up and let it run until it pulled down to -24 degrees C and figured it was good.

The guy I bought the boat from in 2016 left a can of Hychill on board, he is a professional frigi tech. When I asked him where he had used it he replied that he had recharged a friends bar fridge with it and a lot of European manufactured fridges now used hydrocarbon based refrigerants.

When I called Hychill's Melbourne, Australian factory a few years ago to discuss their products use they told me that Europe was their major market.

I notice that Danfoss have a separate product designation for compressors to use hydrocarbon based refrigerants. I cannot perceive why this would be required for the internals of the compressor unless it requires a different varnish on the coil windings. Hychill state that their product is compatible with all current compressor oils.

[Bill O]

Originally Posted by Richard Kollmann

Correct amount of refrigerant in a capillary tube boat refrigerator system

1. What method do you use when adding additional refrigerant to a capillary tube refrigeration system? Then how do you know later refrigerant charge is correct for best performance?

Bill O, an billknny, are not far off for doing it yourself refrigerant servicing as long as they follow it up a day or two later with monitoring frost line and then amperage comparison provided by compressor manufacturer based on compressor speed. It is always better to be slightly low on refrigerant than having added load of too much refrigerant. Twenty five grams too much refrigerant wastes energy. Fifteen grams low on refrigerant may cause compressor to run slightly longer but will have little affect on energy loss.

As mentioned in my normal "performance evaluation", we do watch the frost line and make certain the amp draw is consistent. This is the great thing about having a full time amp meter in line to help monitor the system.



[QUOTE=Richard Kollmann;3094919
When moving boat from a warm climate to a cold climate with a capillary tube system will it require more or less refrigerant in refrigeration system?
[/QUOTE]


Maybe you are writing part II to your original question set, but wanted to double check if my observations were not way off. Since we set up the performance of our fridge in warm weather, we need to up the thermostat when its cold to make the compressor run more consistently.

[RaymondR]

Hi again Richard,

I just read your second posting which must have come up while I was writing mine and found your comments on TVX valves very interesting.

I have been pondering on how one might exploit the resister controlled variable speed capability of the small Danfoss DC compressors to exploit the availability of plenty of solar power during Australian very sunny days for some time now however I perceive one of the issues with this to be the large variation of liquid refrigerant volumes produced downstream of the condenser which a capillary tube may have problems handling efficiently. A TVX valve would appear to be the solution to this. Do you have a recommendation on a brand and model.

Good tip on the amp meter, I had one on my old boat just to be able to see whether the compressor was actually running and not just the condensing fan, had not considered it's use when recharging.

[Grattaway]

RaymondR - just remember that Hychill is a flammable refrigerant whose components are pretty much the same as you have in a propane tank so needs to be used with care in enclosed environments - but as a refrigerant better than the "Freon blends" and with less environmental impact

[Rorzech]

I use R-290 (Propane) very similar to R-12 and R134A I charge it slowly until it frosts back . Once its running steady state then I bleed off a little vapour a little every 3 minutes. I keep doing that until the frost back disappears where the cap line is soldered to the suction line. I want to refrigerate the warm cap line to prevent flash gas inside the capline is it drops pressure traveling along the length of the tube. That will give peak performance.

[RaymondR]

Originally Posted by Grattaway

RaymondR - just remember that Hychill is a flammable refrigerant whose components are pretty much the same as you have in a propane tank so needs to be used with care in enclosed environments - but as a refrigerant better than the "Freon blends" and with less environmental impact

Hi Grarraway,

I'm an old oil driller mate so very aware of how nasty things can get when the LEL is exceeded with hydrocarbon/atmosphere mixtures and there's an ignition source about.

I pondered on the explosive gas mixture aspect of the hydrocarbon based refrigerants for a fair bit before deciding that having 100 or so grams of it in a closed system like a refrigerator was much less hazardous than having 9 kg or so in an open system such as a gas stove.

[masonc]

I have a BD35 air cooled compressor and I had to replace the Waeco box evaporator this week. The documentation said 60g for compressor and 15g for evaporator. I vacuumed the system, put the R134a canister on a little digital scale and added 75g slowly. The system is working very nicely.

[Coolerking]

Originally Posted by masonc

I have a BD35 air cooled compressor and I had to replace the Waeco box evaporator this week. The documentation said 60g for compressor and 15g for evaporator. I vacuumed the system, put the R134a canister on a little digital scale and added 75g slowly. The system is working very nicely.

THIS.

[Richard Kollmann]

Response

Quote:
Maybe you are writing part II to your original question set, but wanted to double check if my observations were not way off. Since we set up the performance of our fridge in warm weather, we need to up the thermostat when its cold to make the compressor run more consistently.
__________________
Bill O.

Bill, I spent 30 years dealing with snowbird boaters who traveled from cold climates in winter and returned every year in the spring. When refrigerators with capillary tubes are serviced with refrigerant by the manufacturer set charge based on standard day temperatures so normal seasonal temperature changes will not greatly effect performance. If you add refrigerant to a cap tube system in the tropics by evaporator frost cover it may be low on refrigerant in a much colder climate. The thermostat on most of these systems control evaporator temperature not box temperature. If you need to change thermostat setting it will be as a result of weak box insulation.

Quote:
I notice that Danfoss have a separate product designation for compressors to use hydrocarbon based refrigerants. I cannot perceive why this would be required for the internals of the compressor unless it requires a different varnish on the coil windings. Hychill state that their product is compatible with all current compressor oils.
RaymondR

I have no information on use of flammable Hydrocarbon Hychill refrigerant use in boat refrigeration. Varnish failure was a problem on older fixed speed Danfoss compressors and on water cooled keel cooler systems. I look at flammable refrigerants for boats as a risk I can avoid.

Quote:
I have been pondering on how one might exploit the resister controlled variable speed capability of the small Danfoss DC compressors to exploit the availability of plenty ofsolar power during Australian very sunny days for some time now however I perceive one of the issues with this to be the large variation of liquid refrigerant volumes produced downstream of the condenser which a capillary tube may have problems handling efficiently. A TVX valve would appear to be the solution to this. Do you have a recommendation on a brand and model.
RaymondR

There are two differences between a capillary tube and a TXV refrigerant flow controls the temperature range of cap tube is limited to size of evaporator. The TXV has unlimited range with adjustable refrigerant flow based on its wide open orifice selection. The TXV insures that no mater what speed compressor runs at the cooling phase change of high pressure liquid refrigerant to saturated vapor where heat is removed occurs inside evaporator. Capillary tube systems refrigerant phase change inside evaporator depends on a small amount of liquid refrigerant available to phase change in evaporator. With evaporator desired temperatures and thermostat setting were the same performance would be the same. The big difference between the two systems id the rate of temperature change is greater with the TXV because of the increased refrigerant flow. The question asked once the cap tube has reached its equilibrium of low temperature flow will allow more flow if compressor speed is increased? The way to find out is to disconnect thermostat wires from module terminal C and T and install a 1500 ohm resistor across module terminals and let compressor run till evaporator temperature hits bottom.

masonc, To verify your BD35 system refrigerant charge is correct check frost cover areas after at least one day of operating with thermostat cycling system.

The evaporator should have at least 90% of its surface area covered with frost. And return line leaving evaporator should not have frost on it outside refrigerated insulated box on its way to compressor. The normal amp draw of the BD35 is from 3 to 5.5 amps running on 12 volts depending on preset compressor speed.

[David B]

From our perspective (freezer repair - new compressor and nitrogen flush to get the oil out of the capillary), it was a matter of filling while keeping an eye on the gauges, then monitoring freezer temp.
This went on for 36 hours before it seemed right (and we saw -18C in the freezer).
Bit of a 'test and see' situation when performance and current draw are important.