Got called to a little Yacht:
Unit description and application: Refrigerant R12 low temp freezer box with two holdover paltes
There are two refrigeration circuit for this unit. two separate condensers, one water cooled and the other air cooled. two different compressors one engine driven and the other compressor sites on a 1/3 hp hermetic compressor commercial condensing Tecumseh unit . two hold over plates are held in the freezer section. there is two TXV's on there respective line sets. from the txv refrigerant then passes to the first holdover then through the exit of the first hold over to the second hold over. I did not see any type of oil return between compressor (over course they are very different) i did not see liquid line solenoid.
When they have 115 volts on shore power then they would run the Tecumseh. (for what i think is one circuit of r12)
When the boat is off shore they use one of the two diesel engines to turn a belt/engine driven compressor (for the what i think is the second r12 circuit)
Interesting fact Tecumseh unit is controlled by a low pressure switch. But the other unit just has a high pressure differential switch and nothing else? i not sure how the second refrigerant circuit is maintaining box temp when out at see. any idea?
Question #1 are the two refrigeration circuits connected? (I did not see any evdnce that lead me to belive that but maybe im missing something)
Question #2. The Tecumseh condensing unit needs to be replace (small receiver leak and bad compressor)
The unit is R12.....so is the TXV. i really want to avoid touching the txv as it seems i will have to remove part of the counter in order to replace it. THAT BEING SAID I AGREE THAT I SHOULD CHANGE THE VALVE OVER TO THE NEXT REFRIGERANT. But i would like to know if i can use a R134a condensing unit and let it run on MP66. MP66 can work on many different oils. what are the problems might i run into if i do this?
try to keep in mind there is a very very limited amount of space around that txv thats why i ask. i know if i buy something r134a then i should really only put r134a.
Just posting for more information. At this point i will replace existing r12 with 404a and change the txv.
Thanks for any info
Also i can just flush system to remove minrale oil and go straight to r134a.....any help is great
I worked on something like that once on a boat. Memory is fuzzy but I am pretty sure both systems were completely independent of each other because I only repaired one of them.
You can try 134a since it is such a small system. Might not be the optimum choice but domestic appliance manufacturers use it for freezers and it is cheap.
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What should i change over to?
what is the reason i cant put mp66 in there?
I work on domestic units and find that it is stander in literature from subzero that there compressor runs in a 2inch (or more at times) at design temp. but thats only for a 0* box.
i dont know much out the brine in the cold plate but i think it needs to be far colder then 0* to get there.
What about setting it up with r134a, adding an accumulator then overcharge a little bit to insure proper super heat back to the compressor?