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killarney_sailor 07-24-2008 11:13 AM

Separate freezer and fridge - two compressors or one?
I check the various threads on refrigeration that have appeared and did not find one that addressed this question, so here goes.

We have decided that we have to replace the ancient Grunert 110v system on our Bristol 45.5. It is our intention to head off for extended cruising in two years so we have been thinking that 12v makes most sense. The boat has a dedicated freezer box (~3.3 cu ft) as well as the refrigerator (~7.8 cu ft). The Grunert has one compressor that services both boxes. According to the Bristol specs there is 6 inches of insulation on the bottom of the boxes, 4 inches on the side and 2 inches on the top. Battery capacity on the boat is substantial and I have a genset, but no solar or wind generation at this point (this good change, as needed).

Are there 12v systems where one larger compressor does both boxes or do we need two smaller compressors? Perhaps the latter is a better idea since you have some redundancy if one compressor craps out on you.

I suspect that personal opinions on good manufacturers depends on one's happiness (or not) with what you have. I have been wondering about Sea Frost since they seem to have such a good reputation, although I must say that I have had very good success with Cold Machines in the past and it would be cheaper to do I think.

Thanks in advance for any comments.

speciald 07-24-2008 11:40 AM

I have the Seafrost 110v., water cooled system. There are two valves so the two bokkes have separate thermostats. There is one plate in the fridge, two inthe freezer. Additionally I have an engine driven compressor - belt and suspenders, I guess. The system has worked without problem for over 5 years. The only problem is that in crudy water the intake for the cooling water will occasionally pick up some debrie and the unit will shut down unexpectedly. The 12 v. unit does not have the capacity to run this system. On the other hand, this setup must have cost about 12K to install.

camaraderie 07-24-2008 12:16 PM

If you plan to have the system professionally installed then I think one hi capacity compressor and two separate plate systems with their own thermostats is probably the most cost effective way to go. If you are DIYing the install, then a couple of prepackaged systems are probably the best choice.

FWIW...I've had two AB units in the past and on the present boat, switched to the Seafrost DC5000 1/2 HP compressor for my large and separate 2 box freezer/fridge system with excellent results. It demands a large battery bank due to current drain, but onl remains on for short periods and freezes the plates in short order due to the current so the net use of electric is quite efficient and you don't have the fridge running 75% of the time in the tropics. Not a cheap system but worth considering given your configuration and large battery bank.
12 VOLT DC 5000 07-30-2008 09:29 AM


We are replacing our similar sized two box (fridge and freezer) Grunert system with an AB Cold Machine. I spoke to an AB tech support guy yesterday and asked him about running two evaporators off one compressor. He said that, while it could be done, it would not be a good idea. I didn't cross-examine him as to the reasons. We've decided to use the freezer box for dry storage and to make do with the freezer capacity of the "large" evaporator in the fridge box.

He also mentioned that the only reason to opt for the "super" (water cooled) machine would be if the compressor had to be installed in a very hot place, like an engine room. Since our compressor will be installed in a fairly large area under the salon settee, his advice was to, cut a ventilation hole in the box and install a louver and a small fan to increase circulation over the compressor. Of course, additional insulation for the box would help as well. Also, by eliminating the water cooling system, I can permanently close up another hole in the hull.

Good luck with your project.

Phil McGovern
s/v Sunshine
PDQ 36

Vasco 07-30-2008 11:38 AM

I have a separate freezer box and a front opening fridge. They work off one compressor and one evaporator plate in the freezer. The fridge works on spillover, via a fan, from the freezer. It's an AB Cold machine and has worked well for the past four years. 07-30-2008 03:36 PM


I should have made it clear that our freezer box is located in the aft cabin -- approximately 10' away from the fridge box which, of course, is in the galley. In this situation, the tech person advised against trying to run two evaporators off a single compressor. He said that it could be done, but we would not be happy. This was how our old Grunert system was set up and it seemed to work OK right up until it died. It did, however, draw a LOT of amps (i.e. 30) and, near the end, ran almost constantly. I suspect it ran out of refrigerant.

Yes, I understand that your approach of dividing one box into two zones, fridge and freezer, is very commonly done and we may well opt to do that later on.

Best wishes,

Phil McGovern
s/v Sunshine
PDQ 36

sailingdog 07-30-2008 03:45 PM


Yes, two compressors are probably a much better idea—given the distance between the two boxes.

killarney_sailor 07-30-2008 04:10 PM

Likely going with two systems
I think I will be going with two independent systems. My two boxes are about 8' apart and with two systems I can put the compressors in different locations to reduce the heat problem a bit.

I got a quote on a Seafrost system that used one compressor but it was just too much $8200! I have installed a Cold Machine and it was not too bad to do. I might go with Adler Barbour again although, from what I have read their customer service is not very good. Will not be very easy to remove the existing system though. as there is a lot of wiring and piping to deal with.

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