Frigoboat freezer problem

[ColdEH]

A digital thermostat will do the same thing as a mechanical one . They both need to control your evaporator plate temperature not the box temperature. If you control your compressor using box temperatures you will more then likely over power your plate and the frost will travel down the suction line to your compressor , this is bad .

If you are getting good frost on your plate you should be getting good refrigerant flow and volume , it sounds like more of a control issue . The first thing I would do is take of the Merlin and let the system run at low speed for a while and see if it cycles normally . If it does, the Merlin was the trouble , if it dosent I would suspect the mechanical thermostat and its connections to the plate . Defrost the system and make sure the sensing tube has not shifted , they need to be held tight to the plate to get a good reading of its temperature. Next would be the mechanical unit itself , they do go bad from time to time and corrosion can be an issue as well, but they are cheap to replace .

I hope this helps a little.

Regards

[ColdEH]

Originally Posted by Streetcar

Just to follow up on this..

The original problem has re-occurred every time I switch the system off for more than a couple of hours. When I switch back on, the plate freezes for about 10 mins and then it seems the capillary blocks and no more freezing on the plate. The only way to get it going again was to evac the system for 24hrs and recharge it.

I think that I have now solved it. New evaporator plate (and cap tube). What happened is that I got someone out to evac the system and recharge it as above and they suggested also backflushing it to remove any possible blockage in the cap tube. What I didn;t know at the time was that they were going to do it with Nitrogen instead of refridgerant. The pressure of the nitrogen inflated the plate like a balloon, so they agreed to replace the plate. Now it all seems to work fine... for now...

My guess is that, as was suggested right at the beginning of this thread, debris blocked the cap tube at the end nearest the compressor. Evacuating the system was enough to dislodge it so I could get going again but it was only ever a temp solution.

Probably the best longterm solution would be to also install a dryer between the compressor and the beginning of the cap tube to stop any more debris finding its way around the system.

Wow!!!

I read this stuff all the time , LOL they blew up your plate with Nitrogen!! You should have taken a picture of that .

I got so scared of installing two new cap tube systems on my boat and then sailing of to far of lands and having troubles like that . So I didn't , I looked around and the only systems out there that didn't use a captube were the SeaFrost and the CoolBlue Technautics systems.


I liked the CoolBlue system , but not the holding plate and Spanish built compressor , I like the Danfoss/Secop compressors , but they did use a thermostatic valve to control refrigerant flow . The valve actually allows more refrigerant flow when the load is higher, like when you first start it up and when you load up your box with warm food or beer . It is also likely to never get blocked , just look at the size of the receiver filter drier . Much better design then a Cap tube system .

The Seafrost system confused me , they use a constant pressure valve to control refrigerant flow , again much less prone to blockage but these things are regulated by the pressure in the plate . They keep it at a constant pressure level , if the pressure goes up the valve slows down the flow of refrigerant to compensate and bring the pleasure back down to the set value. Here's the kicker , what happens when you load up your box ????? the evaporator gets warm .....the pressure goes up and the valve closes and slows down the refrigerant flow trying to restore the pressure to its set point .....Thats working backwards !!!!!!!! You want it to cool more not less when you need it !

These small compressors don't have a lot of power to cool things down fast , but really !??? do you want you what little power you do have to be slowed down by a valve working backwards ???

I designed and built my own

I'm going sailing , and I'm not even remotely concerned about any problems with my refrigeration systems.

The peace of mind was well worth the trouble .

Regards

[hpeer]

I looked at it, I cajoled it, I cursed it, but I didn't TOUCH it. It worked for 2 days fine, then stuck on. Turned it off, turned it back on and it worked fine yesterday but stuck last night. Turned it off, now it's working fine again.

Screw it. I'll look at it next year!

Happy New Year!

[hpeer]

I've ordered a new thermostat, the kind that hangs in the box, simply because I don't have to remove the evaporator to install or replace it.

Not sure that's the issue but it's the easiest thing to change out.

[Typhoon]

You want to attach that thermostat sensor to the plate , if you control your compressor by box temperature you run the risk of over powering your plate and liquid refrigerant getting back to your compressor . That's a bad thing . Compressors don't pump liquids well , boom [emoji95]

[hellosailor]

"The pressure of the nitrogen inflated the plate like a balloon,"
These days it is normal for a really good AC shop to use nitrogen, an inexpensive inert gas, instead of refrigerants, when all they are doing is purging or pressure testing. The nitrogen is inert, clean, non-polluting, and cheap cheap cheap. A shop that doesn't use it, is a dinosaur or ripping you off. (Like the shops that charge you twice the retail price for gas, and claim they needed to use way more than your system can take, because they used it for flushing as well.)
Nitrogen pressure is controlled like anything else, that shop just screwed up with how they used it. FWIW.

[Typhoon]

Originally Posted by hellosailor

"The pressure of the nitrogen inflated the plate like a balloon,"
These days it is normal for a really good AC shop to use nitrogen, an inexpensive inert gas, instead of refrigerants, when all they are doing is purging or pressure testing. The nitrogen is inert, clean, non-polluting, and cheap cheap cheap. A shop that doesn't use it, is a dinosaur or ripping you off. (Like the shops that charge you twice the retail price for gas, and claim they needed to use way more than your system can take, because they used it for flushing as well.)
Nitrogen pressure is controlled like anything else, that shop just screwed up with how they used it. FWIW.

We use nitrogen to evacuate our systems , Its a great way to get things going and removing any moisture before filling a system with refrigerant . You never want to introduce air , air carries moisture .

That being said , you really need to watch your pressures when you are using nitrogen , and not exceed the systems maximum pressure , even when testing for a leak. The pressure in the tank can easily blow up any system . Thats why the tanks have gauges , high and low . You must be cautious.


Regards John

[pcmm]

Originally Posted by s/v Jedi

When you saved the plugs and caps that were on the lines of each component, you will find an O-ring on each plug. I also believe they are a standard size so you can match them in any hardware store.

I wish that were the case, the o-rings are metric and a very hard to find size, even here in Canada ( land of Metric) I looked for weeks and eventually gave up and ordered them from a frigoboat dealer. ended up costing me close to $36 shipped to get enough o-rings to renew all my connections and have spares ( I think it was 6 o-rings)

[Typhoon]

Originally Posted by ColdEh Marine

We use nitrogen to evacuate our systems , Its a great way to get things going and removing any moisture before filling a system with refrigerant . You never want to introduce air , air carries moisture .

That being said , you really need to watch your pressures when you are using nitrogen , and not exceed the systems maximum pressure , even when testing for a leak. The pressure in the tank can easily blow up any system . Thats why the tanks have gauges , high and low . You must be cautious.


Regards John

Here's a picture of my nitrogen tank gauges . 8000 psi . That will do it

Regards

[hellosailor]

" Thats why the tanks have gauges " And a really sharp monkey would have a regulator on that tank as well, to ensure it wasn't going to put out too much pressure. Complete sets (one fitting with regulator, tank gauge and outlet gauge) all together commonly sold for $50 in the home brewing and home carbonation shops. Surely there's something similar for nitrogen tanks.

[Typhoon]

Originally Posted by pcmm

I wish that were the case, the o-rings are metric and a very hard to find size, even here in Canada ( land of Metric) I looked for weeks and eventually gave up and ordered them from a frigoboat dealer. ended up costing me close to $36 shipped to get enough o-rings to renew all my connections and have spares ( I think it was 6 o-rings)

O rings in a refrigeration system as a final seal , is a bad idea. Try not to buy a system designed like that . If a manufacturer gives you spare parts, then they know those parts will fail. Not a problem if it is not a part that holds the refrigerant in , you cant just put a new one. First your whole system fails , you lose all your food , then you have to find a tech to install the new O rings, braze in a new filter drier, vacuum the system, and then recharge the system to the exactly the right volume, all this while making sure everything is absolutely spotless and not introducing any dirt into the system. Remember as he is brazing in that new filter drier he should have a nitrogen purge running so there is no heat induced scale being formed on the inside of the tubbing . If there is any dirt or moisture left in the system when he recharges it , one day some time down the road , that dirt will find its way to the captube, and plug it , your system is down again and you have to do this process all over again.

Try to find a tech in the that far off place that you are in , ok maybe you find one. Is he really skilled enough to do this job properly ?? If he is , what will this all cost you ? This is why when a failure like this happens most people just replace the entire system.Its the only way to be sure. Ok so that means if you are buying a system prone to these kind of failures that this system is disposable ?? Really?? How much did you spend installing this system ? How much did the system cost in the first place ? The average life span of those O rings is 5 years, maybe less if you are a full time cruiser and your system runs hot , more if you are a weekend sailor . They just dry out and crack .

Sorry for the ramble .

Regards John.

[hpeer]

Follow up to above issue....since I ORDERED the new thermostat (but not recieved much less installed) the damn thing seems to have been working properly. Not immediately mind you, but a couple of days later it started behaving.

Coincidentally I replaced my battery bank of 4-GC2 batteries. They were about 5 years old and not keeping a good charge.

I'm at a loss as to why low battery voltage would cause the thermostat to work improperly. Voltage would get as low as 12.2 on occasion. But freezer box was still iced over.

All just a crule coincidence to confuse and befuddle?

[ayates]

Originally Posted by ColdEh Marine

O rings in a refrigeration system as a final seal , is a bad idea. Try not to buy a system designed like that .

It appears to me that all these systems utilise quick connectors for the refrigerant lines, and all of them have 'o' rings. I think it would be nice if some manufacturers/vendors offered an option for brazed connections. Just one less thing that can go wrong. (I do get that the customer would lose self installation and that removal of the system could require cutting/re-brazing).


Allan.

[Typhoon]

Actually if you take a close look at those resealable couplers they actually have a metal to metal seal . The o rings you see are just to seal them when you disconnect them . The leading edge of the male coupler actually cuts into the seat on the female . That's why the install directions tell you to mark the coupler and then give it that last 1/4 turn once you have seated it . That seals it up quit well if done correctly .
But you are correct , the best way is to have a completely brazed system with no couplers . That can be done but its not for the self install crowd .

Regards John Tully