Frigoboat freezer problem

[Streetcar]

The compressor on my Frigoboat freezer does not stop running even through the unit is freezing. Then occasionally when I start it up it runs continually but does not cool the plate at all.

The unit is a Frigoboat K35F (keel cooler) with aluminum evaporator plate.

Most of the time it cools the evaporator plate to 10F (-12C), but the mechanical thermostat doesn't stop the compressor. I have fitted a new thermostat but it still runs continually. Should the thermostat cut the compressor at these temperatures, or is the plate not getting cold enough for this thermostat?

To complicate things, occasionally when I power the freezer up the plate cools a little but does not freeze. The compressor continues to run but the evap plate gets no colder. The compressor gets hot enough for me not to be able to keep my hand on for more than a second or two.

This indicates low refridgerant to me, but then...

If I let everything cool down and restart it freezes and runs OK (although still without the thermostat switching).

Any help very appreciated as I am in a remote place and can't get a fixer in for this one.

[Richard Kollmann]

Sounds like a typical Frigoboat refrigerant flow problem evaporator will sometimes form frost all over its surface area and other times cool but no frost. If evaporator at times has frost covering 85% or more of its surface area the problem is not low on refrigerant.

If evaporator is cool but no frost at times refrigerant flow is restricted do to moisture in refrigerant freezing and thawing in cap tube flow control device. If any one has tampered with refrigerant in your unit moisture probably interred system then.

Because there is no filter protection ahead of cap tube on this model small debris from keel cooler to large to pass through control tube will sometimes block tube entrance. If you confirm that it is mechanical restriction and not ice Frigoboat as a temporary fix suggests tapping on line at cap tube area to cause particle to fall backwards into larger tube area.

[Streetcar]

Hi Richard, many thanks for your response.

On your first point: The evaporator has 100% frost when it freezes. There is also frost on the return line to about 2ft past end of insulation - but this does not reach anywhere near the compressor. Does this indicate refrigerant is overcharged and would that also explain the fact that the plate does not freeze sometimes?

On the second point: The unit was recharged by a refrigeration technician in Fiji 3 months ago. So yes, it is possible moisture got in.

On the third point: I will investigate this.

[Richard Kollmann]

Unless you are presently in a cold climate there should not be frost on refrigerant tubing outside refrigerated area, but I do not think refrigerant volume is your problem.

If it is moisture blockage and only cold condensation moisture on evaporator you should be able to hear inside box noise of flow stop and start as ice melts and refreezes. This cycling of freezing and thawing may take 5 to 10 minutes. If moisture is the problem it will take extended dehydration with a refrigerant vacuum pump to boil it out of complete system.

Do not consider the third point until you have eliminated the moisture Question as tampering with refrigerant is always the sign refrigerant has been contaminated on an unfriendly Frigoboat keel cooler unit.

[s/v Jedi]

+1 on Richard's assessment that it is probably moisture. I had the same problem with two of my three units and solved it by evacuating with a vacuum pump while using a heat gun to trace and heat all refrigerant lines, the compressor itself, the tiny filter dryer behind the compressor and the evaporator plate several times. The heat gun promotes boiling the moisture out.

I did this 2 years ago and the problem has not returned

Originally Posted by Richard Kollmann

Unless you are presently in a cold climate there should not be frost on refrigerant tubing outside refrigerated area, but I do not think refrigerant volume is your problem.

If it is moisture blockage and only cold condensation moisture on evaporator you should be able to hear inside box noise of flow stop and start as ice melts and refreezes. This cycling of freezing and thawing may take 5 to 10 minutes. If moisture is the problem it will take extended dehydration with a refrigerant vacuum pump to boil it out of complete system.

Do not consider the third point until you have eliminated the moisture Question as tampering with refrigerant is always the sign refrigerant has been contaminated on an unfriendly Frigoboat keel cooler unit.

[Streetcar]

Thanks guys, I appreciate your help.

As I mentioned previously, on most occasions the freezer seem to operate fine bringing the evaporator plate down to 10F or so. The problem, in this case, is that the thermostat does not cut out at this temp and the compressor runs continuously.

The non-freezing issue of the plate is only very occasional when the system is switched on.

Is this all consistent with your suggestions?

[Richard Kollmann]

Streetcar, because Frigoboat located filter dryer on return line at compressor instead of where it should be, heat from compressor will discharge moisture from dryer into compressor. Small filter dryers contain absorbent so once it heats up with compressor stopped moisture is returned to circulate through system. This could account for ice restricted flow after another system start up. Another possibility is that moisture can be frozen inside evaporator as long as it is below freezing and then released to again circulate when evaporator warms up.

Remember thermostat on this type system does not directly control box temperature it controls evaporator temperatures. On a refrigerator with thermostat set to mid range evaporator temp is around +12 degrees F so box temp can be around 30 to 40 degrees. Freezer thermostats control evaporator temp at zero and below. If refrigerant flow is restricted for any reason or there is excess refrigerant evaporator temperature may not ever reach thermostats desired set point.

[Streetcar]

I am going to get a local technician to evacuate the system and hopefully remove any moisture. He is very keen to add a product called "Thawzone - Moisture Control". I am very wary. Is it a bad idea? If so, what is the best procedure for drying the system? Heat gun would be very difficult to operate in the confined spaces.

[s/v Jedi]

Originally Posted by Streetcar

I am going to get a local technician to evacuate the system and hopefully remove any moisture. He is very keen to add a product called "Thawzone - Moisture Control". I am very wary. Is it a bad idea? If so, what is the best procedure for drying the system? Heat gun would be very difficult to operate in the confined spaces.

A vacuum is the primary tool to remove the moisture as it will boil out. The heat gun is easier to bring to the compressor than a screwdriver to fasten it so I'm sure you'll manage that The idea is that you both pull a vacuum which lowers the boiling point of water plus add heat to make sure it evaporates from the oil. Do not let any local technician add anything else than new, clean refrigerant.

[Richard Kollmann]

If you have confirmed that there is moisture in refrigerant by the test I described vacuuming to boil off water is the correct solution.

Thawzone is a brand of alcohol that when added to refrigerant will lower freeze point of water like antifreeze. Thawzone has been around for many years used in refrigeration mechanical compressors for moisture control. Instruction on bottle state “For use with all refrigerants and refrigeration lubricants including 134a. Directions for use, Add directly to refrigerant 1/8 ounce Thawzone per pound of refrigerant in system”

I have used Thawzone in the past on engine driven systems but never in systems with electrical field wiring inside compressor because it might destroy coil wiring’s insulation. To use Thawzone in a Danfoss BD 12 volt compressor would not be my decision, even if it got refrigerant to flow again moisture is still there to cause corrosive sludge. At a mixture rate of 1/8 ounce per pound with a Frigoboat unit containing only about 3 to 4 ounces of refrigerant the addition of Thawzone would not be in fractions of one ounce but drops of liquid.

[redsky49]

Originally Posted by Richard Kollmann

Remember thermostat on this type system does not directly control box temperature it controls evaporator temperatures. On a refrigerator with thermostat set to mid range evaporator temp is around +12 degrees F so box temp can be around 30 to 40 degrees. Freezer thermostats control evaporator temp at zero and below. If refrigerant flow is restricted for any reason or there is excess refrigerant evaporator temperature may not ever reach thermostats desired set point.

Therefore, if I have difficulty currently maintaining refrigerator setpoint on my Frigiboat system (evaporator is 23 degrees when refrigerator is set for 39.2 degrees, and the unit runs constantly trying to catch up), I can lower the evaporator temperature?

How does this work?

Old thread,but I am looking for some help with my system too.

[senormechanico]

We have a keel cooled Vitrifrigo with a BD35 compressor (same unit as far as I can see).

A bit of insulation around the evaporator works great.

I used a single 10mm layer of Aerogel (left over from the box build) after sealing it with our Vacu Fresh.

I experimented and found that covering just the bottom worked the best.

A couple of long zip ties around the evaporator did the trick.

Now we can keep ice cream rock hard and the fridge sits at 40 degrees.

Steve

[Richard Kollmann]

Redsky 49, If compressor runs continuously and evaporator temperature will not drop below 23 degrees it is not the thermostat's fault. Two hours of running time continuous should produce below zero F evaporator temperatures. What type condenser do you have? Problem could be poor condenser cooling or low or too much refrigerant. Describe your system air or water cooled or Keel Cooler. If keel cooler, is it's exterior clean. There is also a problem on these keel cooler models do to refrigerant flow blockage caused from material coming out of cooler. If condenser is air cooled has it been cleaned of dust and hair recently.

[redsky49]

Keel cooler. We went back in the water in December, so I don't think there is much fouling but I will check for sure tomorrow.

I defrosted this weekend, but that had no effect. Also looking at whether the box is overloaded with groceries. Don't think that is the case.

My concern is that the system had formerly worked quite efficiently before, but now seems to labor. Rechecking the coil, I see that there is temperatures near 10 degrees at the bottom of the coil, with temperatures closer to 30 degrees at the top. 23 degrees was a mid coil measurement. Is this a typical delta? This is a 40"(?) long coil, placed horizontally around two sides of the box - about 6-1/2 cub. ft. capacity box. Seems to be an equal layer of frost on the coil.

Top of compressor now is about 143 degrees.

One more thing, at one of the refrigerant line fittings there is a little blue discoloration as if something has been leaking.

System was installed in 2005 by yours truly, but recently had not been used for a couple years. Seals dried out and leaking?

Appreciate the help!

By the way, we are currently in Florida

[s/v Jedi]

Originally Posted by redsky49

Keel cooler. We went back in the water in December, so I don't think there is much fouling but I will check for sure tomorrow.

I defrosted this weekend, but that had no effect. Also looking at whether the box is overloaded with groceries. Don't think that is the case.

My concern is that the system had formerly worked quite efficiently before, but now seems to labor. Rechecking the coil, I see that there is temperatures near 10 degrees at the bottom of the coil, with temperatures closer to 30 degrees at the top. 23 degrees was a mid coil measurement. Is this a typical delta? This is a 40"(?) long coil, placed horizontally around two sides of the box - about 6-1/2 cub. ft. capacity box. Seems to be an equal layer of frost on the coil.

Top of compressor now is about 143 degrees.

One more thing, at one of the refrigerant line fittings there is a little blue discoloration as if something has been leaking.

System was installed in 2005 by yours truly, but recently had not been used for a couple years. Seals dried out and leaking?

Appreciate the help!

By the way, we are currently in Florida

Ha! Do I recognize that or what! I installed three units in early 2005 and all three started leaking at the quick connect fittings in 2012. You need to replace the O-rings in every connection (every 5 years would be safe interval); I used the spares that come with the units. After that, evacuate, test for leaks and refill using manufacturer method. I recommend to read those so that you can keep an eye on the tech. I did it myself and followed Richard's advice on using a heatgun to promote the moisture boiling out of the compressor oil. They work like new again.

good luck!
Nick.