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Old 02-13-2011, 08:15 AM   #21
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RE: Nova Kool? Dometic? Norcold?

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Forkliftt wrote:

.....There is NO info online to tell you what pressure to recharge to....
Interesting.* I checked on our BD35 and all is says is to charge 6.5 oz*with 134A.* No pressures mentioned.* If you find out please post.

*
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Old 02-13-2011, 08:22 AM   #22
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Nova Kool? Dometic? Norcold?

When I "inherited" my MT34, a previous owner had installed an apartment-sized 120v Haier fridge.* Admiral loves having all that space, and since we are marina cruisers, it runs on shore power at home and at marina stops, and with a* dedicated 2000w inverter under way.* It's at least 9 years old, and shows no signs of rust or other deterioration from a marine environment.

We also carry a Honda 1000 genset for times when we do raft-ups, etc. and want to keep it cold.

You other MT34 owners will note that the port side of the salon was also modified to remove the upright cupboard and* settee, replacing with the fridge and a nav desk.

It's about 10 cu.ft. draws 11 amps. and probably cost $250-$300.* A look at Defender shows a 7 cu.ft. Norcold for $1280.* What am I missing?


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Old 02-13-2011, 08:33 AM   #23
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RE: Nova Kool? Dometic? Norcold?

ARoss,
I would put the bigger unit in today if I had room.
Larry,
My sweet spot seems to be around 5 degrees low side, 138 high side. I am not an AC tech, but I feel it could stand a little more. After charging my freezer coils were running down to minus 5 DF, that seems sufficient.
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Old 02-13-2011, 08:34 AM   #24
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RE: Nova Kool? Dometic? Norcold?

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Larry M wrote:No pressures mentioned.* If you find out please post.
That is because small hermetic systems are hypercritical as to the quantity of refrigerant in the system.

If you don't have a recovery system and a "dial-a-charge" and know exactly what you are doing - don't mess with it. You will create more problems than you will ever solve.

This is one of the few items on your boat where, unless you are trained, equipped, and certificated you should just leave it alone and call in a professional.
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Old 02-13-2011, 09:06 PM   #25
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RE: Nova Kool? Dometic? Norcold?

Thanks Rick for pointing that out. I should mention that several months ago that only after several other checks, including shooting temps on the compressor and coils, confirming no leaks on the door seals and pulling the unit from the boat cabinet to assure I had sufficiant air transfer did I make the decision to tap into the freon circuit to attempt to charge it.My thinking was that for $150 I didnt need a professional to tell me there was no way to charge it. At $1100, and it not working anyway, I didn't have much to loose. I added freon and the fridge worked a couple of months. And cooled better than it had new.




When I got the boat late friday PM I had gathered supplies and was ready to try this again. I used the sniffer in the upper and lower cabinets, showed no leak, then sniffed near the compressor and my recently installed saddle taps. No alarm.
I promptly hooked up my borrowed gauges and proceeded to accidently overcharge the ststem, I turned it on and the compressor came on line for about 2 seconds and stopped. The fan continued to run and 30 seconds later the compressor fired up again and stopped again same as before. A few more tries and the same result and I realized I had WAY too much freon (true).
I pulled the line from my freon tank and cracked both the Hi and Low valves and allowed the excessive pressure to escape (true). It soon became clear that my saloon was beginning to fog up with the bleed off. Interesting enough- I felt the ambient temperature around me start to rise and the water in the toilet in the front head rose about an inch (BS). Climate change maybe?
I'm not sure, but I opened the stbd door and put a fan near it to let it escape.
I was very tired by then, so I went on to bed. Woke up around 6:30 refreshed and the first thing I noticed drinking my Community Coffee was that I had charged the unit with R22 (should be 134a). I had the 22 there to freshen up my front AC unit (true). Dammit!
Needless to say, I put the fan by the stbd door again and proceeded to evacuate the entire system. I shot some 134 in and evacuated it again. Another shot, kicked the compressor on, then back off again and after evacuating it this time I charged to the correct pressure with 134a, where it is cooling great (true)! Ran it all night and all day today and everything appears to be fine. Say Rick, where can I get one of them there "dial-a-charges" at. Just in case (BS)?
He He He*
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Old 02-14-2011, 04:55 AM   #26
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RE: Nova Kool? Dometic? Norcold?

It's about 10 cu.ft. draws 11 amps. and probably cost $250-$300. A look at Defender shows a 7 cu.ft. Norcold for $1280. What am I missing?

NOTHING,

For a Marina to Marina life style , you got it just right!!
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Old 02-14-2011, 05:34 AM   #27
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RE: Nova Kool? Dometic? Norcold?

Now I hope you have logged the discharge of all that frig gas with the EPA and you have a licence for doing so.
I don't know about the USof A but in Aus these days that is a criminal offense.

But s..t you gotta get the beer cold.

Benn
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Old 02-14-2011, 07:04 AM   #28
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RE: Nova Kool? Dometic? Norcold?

Quote:
Forkliftt wrote:






...proceeded to evacuate the entire system. I shot some 134 in and evacuated it again.

How did you evacuate the system?**When we had a previous unit serviced, the technician used a vacuum pump to pull all the old gas, contaminates*and moisture out before recharging.

*
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Old 02-14-2011, 09:25 AM   #29
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RE: Nova Kool? Dometic? Norcold?

Larry,
They make an AC evacuator pump.
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Old 02-14-2011, 12:47 PM   #30
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RE: Nova Kool? Dometic? Norcold?

On our recent cruise, I "fixed" the interior light in the Isotherm fridge which had never worked. A day or so later the admiral complained that everything was frozen although she had turned it down to "1".

My "repair"*had ensured that the interior light didn't turn off when the door was closed and, since the light is*right next*to the thermostat, the fridge just kept on cooling. I did wonder why the batteries were sinking a bit at anchor, when the solar panels normally keep them up.

So* now I can convert the fridge into a freezer simply by putting the light bulb back in!

I also discovered that the freezer (the real one) doesn't enjoy being defrosted with a ball-peen hammer. The temp probe is unduly sensitive!
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Old 02-14-2011, 12:49 PM   #31
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RE: Nova Kool? Dometic? Norcold?

Someone above suggested hiring a pro and the last few posts make that seem like very good advice.
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Old 02-14-2011, 12:55 PM   #32
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RE: Nova Kool? Dometic? Norcold?

Quote:
Bendit wrote:I also discovered that the freezer (the real one) doesn't enjoy being defrosted with a ball-peen hammer.
A ball peen hammer is OK, just*align a large flat blade screwdriver between it and the evaporator.

*
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Old 02-14-2011, 09:52 PM   #33
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RE: Nova Kool? Dometic? Norcold?

Good read in this months PMM. S D'Antonio did a piece explaining the difference between an AC unit and a DC/AC. Basically the DC has a multi-speed condenser for greater efficiency then the AC units.
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Old 02-14-2011, 10:01 PM   #34
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RE: Nova Kool? Dometic? Norcold?

Perhaps there are different kinds of AC/DC units. I have always been told that the AC/DC units are all AC, but they have inverter circuitry in them so they can run "on" DC. That's one of the things the repair shops who work on Norcold units--- or used to--- in the Seattle area told me they don't like about them. They apparently use a bizarro (their word) 20-volt or 24-volt AC motor.
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Old 02-15-2011, 07:14 AM   #35
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RE: Nova Kool? Dometic? Norcold?

Quote:
Marin wrote:

Perhaps there are different kinds of AC/DC units. I have always been told that the AC/DC units are all AC, but they have inverter circuitry in them so they can run "on" DC. That's one of the things the repair shops who work on Norcold units--- or used to--- in the Seattle area told me they don't like about them. They apparently use a bizarro (their word) 20-volt or 24-volt AC motor.
I have the manual for my Nova Cool here on the desk.* The only difference between the 12V model and the 120V / 12V models according to the wiring Schematic is in the dual voltage unit it has*a*power supply box*that is in the system that the 12V from the battery goes into and 120V from the shore power goes into*then 12V exits to the compressor control module.** All test procedures refer to 12V only at the control module.

Anyone that needs the manual I would be willing to FAX it to them it is eight pages.

*
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Old 02-15-2011, 08:04 AM   #36
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Nova Kool? Dometic? Norcold?

Quote:
Marin wrote:Perhaps there are different kinds of AC/DC units. I have always been told that the AC/DC units are all AC, but they have inverter circuitry in them so they can run "on" DC. That's one of the things the repair shops who work on Norcold units--- or used to--- in the Seattle area told me they don't like about them. They apparently use a bizarro (their word) 20-volt or 24-volt AC motor.
Nearly all the modern units use the Danfoss BD brushless DC compressors. These are variable speed permanent magnet rotor machines that use a fairly sophisticated commutation system that is in many ways identical to the power controls on diesel electric propulsion.

The motors are DC, the voltage into the motor on the Danfoss units varies from 27 to 45 VDC to control speed. There are three wires going into the motor so that might be why some people think it is an AC motor. That and the fact that that little box on the side of the compressor contains both a converter to turn AC into DC, and an inverter to*generate the DC pulses that drive the motor.

Unless the tech is stuck in the 60's there is nothing "bizarro" about the units. They are amazingly efficient compared to the older single speed machines.

*


-- Edited by RickB on Tuesday 15th of February 2011 09:05:57 AM

-- Edited by RickB on Tuesday 15th of February 2011 09:07:28 AM
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Old 02-15-2011, 02:18 PM   #37
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RE: Nova Kool? Dometic? Norcold?

Quote:
RickB wrote:
The motors are DC, the voltage into the motor on the Danfoss units varies from 27 to 45 VDC to control speed. There are three wires going into the motor so that might be why some people think it is an AC motor. That and the fact that that little box on the side of the compressor contains both a converter to turn AC into DC, and an inverter to*generate the DC pulses that drive the motor.
Would this basic description apply to the Norcold AC/DC units too, or at least Norcolds from the late 90s?* It was the Norcold specifically that the service shops in this area didn't like because (among other reasons) of what they considered to be a very odd motor setup.

*
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Old 02-15-2011, 03:05 PM   #38
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RE: Nova Kool? Dometic? Norcold?

Quote:
RickB wrote:The motors are DC, the voltage into the motor on the Danfoss units varies from 27 to 45 VDC to control speed. There are three wires going into the motor so that might be why some people think it is an AC motor. That and the fact that that little box on the side of the compressor contains both a converter to turn AC into DC, and an inverter to*generate the DC pulses that drive the motor.
Rick,

Is the control module where the 12V gets to 27V?
*
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Old 02-15-2011, 03:45 PM   #39
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RE: Nova Kool? Dometic? Norcold?

Quote:
Marin wrote: Would this basic description apply to the Norcold AC/DC units too, or at least Norcolds from the late 90s?*
The older Norcolds with the tall beancan*looking compressors were AC, about 20 volts if I recall correctly. They used a solenoid sort of vibrating slug compressor. It wasn't really a motor in that it didn't rotate.*
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Old 02-15-2011, 03:57 PM   #40
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RE: Nova Kool? Dometic? Norcold?

Quote:
JD wrote:Is the control module where the 12V gets to 27V?
*Yes, that little box on the side of the compressor has the ciruitry that converts AC to DC that is then sent along to a 6-pole IGBT (insulated gate bipolar transistor) inverter that sends carefully timed*pulses to the field of the permanent magnet motor that are phased to create a rotating magnetic field that turns the armature that drives the compressor that pumps the refrigerant that cools the beer.

The things are magic. They measure the back*EMF to determine the load and speed and make adjustments to the phase and timing of the pulses to manage the operation. they run from around 2000 rpm up to about 3500, 27 volts for low speed and linear up to 47 for full speed.*If you have one running on a 24 volt system that alway hangs around*27 volts it will never revert to AC operation ... funny little unintended effect*of the control circuit. I think Danfoss cleaned up on that design and their patents.
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