Author Topic: Correct High/ low pressures for a bd 35/50. No frost on evaperator!  (Read 12370 times)

heron

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I have a Alder Barber unit that I am assuming has a Danfoss 35 compressor because it has the electronic circuit board and led for trouble shooting. The space is to small to see any labels on the compressor.

The boat sat for three years before I bought it. When I got the boat the evaporator did not get cold. The high/low pressure was 90psi/20psi. I didn't have time to evacuate the system so I added R134a to the system and the pressure went too high. About 47psi on the low side. The LED was then flashing three times. I then removed some refrigerant. Down to high and low pressure are 105psi/40psi. The outside temp was 18C .

Now the LED stopped flashing and the compressor runs and I can hear fluid moving in the evaporator, but I get no frost and it is not really really cold.

What should the correct pressures be? Is it different from automotive A/C of high 150psi and low 35psi?

I am thinking that I should start from the begining and apply vacumm to the system and then add new refridgerant.

I have a small basket type evapoator. How much refridgerant should the system take? There is a tag that says 80grams, but that seems like a small amount.

Any tips would be a great help.



Richard

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #1 on: June 01, 2012, 06:30:54 pm »

ANSWER:

You have an Adler Barbour and it will have a BD50 compressor. You also do not understand the difference between Air conditioning and Refrigeration gas pressures.
The refrigeration process must occur in the evaporator and not in the suction line. The problem is contaminated refrigerant or too much refrigerant.  On this small system with a capillary expansion device, it is serviced at the factory by grams of refrigerant not ounces or pounds as you have done. The correct charge for your unit is 80 to 120 grams depending on evaporator size. If refrigerant charge is off 15 grams either way unit will not perform at its best.

At this point it is too late to go by high and low pressure. When a system is not running pressure in system has only one meaning and that is there is some amount of refrigerant in this type system. When a system is running with correct amount of refrigerant high pressure will depend on condenser’s ability to remove heat enough to maintain correct high pressure. Low pressure side of system determines a corresponding temperature of cooling work being accomplished. Suction pressure is not going to be constant. For refrigeration using 134a refrigerant correct amount suction pressure my be as high as 10 psi as compressor keeps running and evaporator cools suction pressure drops and if compressor runs long enough pressure can be zero and evaporator temperature of well below zero.. Normally with thermostat set at mid range suction pressure will be 5 to 6 pi when thermostat stops it.  Then evaporator temperature will reach 10 to 12º F.

Enough about pressure forget you won’t need it any more. Remove your gauges and replace servicing cap on high pressure servicing port.
 
Action recommended, to remove excess refrigerant.
•   Stop compressor and remove a very small amount of refrigerant. Run system 15 minutes check frost line it should not extend more than a few inches outside the box in cold weather, in warm weather only condensation might be present outside the box on return line to compressor. If there is still too much frost stop compressor and repeat process as many times as necessary. When operating properly there must be a layer of ice forming over 90% of the evaporator.  If too much refrigerant is removed there will be an area of the evaporator without frost.
•   Ounce the system is operating OK set the thermostat to full cold for at least 12 hours. If at the end of this test run the evaporator has lost its frost and the evaporator is cold with only condensation on it there is moisture in the refrigerant or refrigerant is contaminated do to poor servicing procedures.
•   If letting out refrigerant did not solve the performance problem or system freezes up do to moisture a refrigeration vacuum pump will be required to remove air, and dehydrate moisture or incorrect gases.

The important step is to stop compressor each time refrigerant is removed to prevent air from being drawn into the system. At some point letting out a small amount will reduce the frost line a lot.  The amperage draw for this unit should now be reducing as it enters a more efficient operating range. Because there is so much refrigerant in your system the above process may take several hours to accomplish.






heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #2 on: June 04, 2012, 01:23:24 am »
Hi Richard,

Thanks for the education I will start the process to get this fridge working and follow up with details of how it goes.

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #3 on: June 25, 2012, 12:55:57 pm »
Update slow in comming. I have not been able to get to the boat much over the last few weeks, but I have some possitive and negative results.

First, I went back to the start and vacumed the system for 12hrs and the system held a vacume for 1hr after the pump was removed. I then put 80grams ( that is what a tag on the compressor listed) of R134a refridgerant into the system. I then did the 15min test and the evaporator had frost over the whole bucket.  It did make a whooshing sound in the evaporator ( is that normal? ).  I then started the sytem and left it on high for 24hrs and more good results all of the pop I had left in there was burst. I was very happy with the results. I had spent some time getting more insulation around the box and it seemd everything was working well. I could not confirm if there was frost on the lines as it is wraped with rubber insulation is not in a viewable postion.

So this past weekend I loaded up the box with food and drinks and set out for a sail. All was good Friday night. Things were getting cold. Then in the morning I noticed that the evaporator was not frosty anymore. I checked the compressor board and the LED is flashing 3 times.

So I looked at Richard's trouble shooting page and 3 flashes could indicate too much refridgerant, overheating, or turning it off/ on too fast. I was carefull to allow 10 seconds before turning the system back on again, and over the weekend even left it off for hours at a time only to find 3 flashes again. The temp was not hot on the compressor or in the boat 70 F during the day.  This left only too much refridgerant in system. I could have introduced contaminates back into the system when I charged it? I was cognisant of purging the manifold, but after reading more of Richard's techniques I am not sure.

I tried bleeding the system in small amount to see if the compressor would start, but not go.   The one thing I did notice was the gas coming out of the system did not smell like R134 and was not very cold on my hand. I only noticed this because one time I released some gas it was cold and this got me thinking. Do I have a leak or is the compressor drawing in air somehow and pressurising the system. Maybe the schrader valves are leaking? I did have the caps on them.


At this point I am at a loss of what direction to go from now.  I will start by looking for a leak in the system and see what I find.




« Last Edit: June 25, 2012, 01:58:43 pm by heron »

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #4 on: June 25, 2012, 01:11:02 pm »
One more thing that I thought of is that my capillary tube from my thermostate is wedged to contact the evaporator, but no clip to hold it in place. Does that need to change? Also, the compressor dosn't cycle, but I thought that was normal when the fridge is loaded with a bunch of warm food?

Richard

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #5 on: June 25, 2012, 07:36:20 pm »
Sounds like you need to start over three flashes of LED is telling you there is an amperage overload.

Amperage overload is most often caused by too much refrigerant or poor condenser cooling.

Thermostat's off cycle must be 3 to 5 minutes if not restart will cause an overload.

Low on refrigerant is not an overload.

Refrigerant blockage will not cause a three LED signal unless too much refrigerant and a blockage at the same time exist.


heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #6 on: June 26, 2012, 01:55:40 am »
I will start over and follow your recomendations in the "amount of refrigerant" section. Thanks for all the great info. Richard would you the 12/24v book as the best resource for sail boat refrigeration?

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #7 on: June 26, 2012, 09:51:27 pm »
Question: Should the compressor start when the system is under vacume?

Today I exausted the system and applied a vacume of 29". I also heated the evaporator while I vacumed the system to aid the moisture to leave the  system.  I then tried to start the system and I still got a three flash LED.  The system held vacume for the next 1 1/2 hours. I will see tomorrow if the vacume has changed.

Richard

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #8 on: June 26, 2012, 10:07:00 pm »
Why would you want to start compressor when vacuum pump is connected?

Add refrigerant until pressure in system is 40 to 50 Psi then stop adding refrigerant and turn compressor on. Wait 10 minutes and add refrigerant until low pressure is 6 to 8 psi. DO NOT add refrigerant after 20 minutes running time.  Disconnect gauge and replace self sealing cap......

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #9 on: June 27, 2012, 12:06:48 pm »
My thinking for running the compressor while the system has a vacume (with the guage manifold closed) was to establish if there was another blockage in the system that was causing the compressor to over current.  If the compressor would not start beause there was too much refrigerant then I thought maybe it should start with nothing in there or a no start would signify another issue.

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #10 on: June 27, 2012, 11:01:46 pm »
I started from scratch today. I vacumed the system, purged the manifold and lines, but I still have a over current 3 flash Led.

Richard I have ordered the 12v book. Is the trouble shooting of a problem like this covered in the book? Any sugestions of where to start to solve the problem?

Question: Should the system hold 29" of vacumm over night or does this signify a leak? There could be leaks in the manifold and hose so maybe it is hard to say.

Richard

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #11 on: June 28, 2012, 07:46:46 am »
Are you saying, you followed my instruction after vacuuming “Add refrigerant gas, only refrigerant can upright no liquid, until pressure in system is 40 to 50 Psi then stop adding refrigerant and turn compressor on”. And after starting compressor LED started flashing? Yes or No?

Your first report listed high and low pressures so unit must have a high pressure service port, what were both pressures in this test when LED first started to flash? This will indicate if there is a refrigerant flow problem or a mechanical failure.

No the book is not going to help you with this problem.

If system will not hold a vacuum is a secondary problem stay with one problem at a time. As system set under vacuum there can be a small decrease in vacuum.

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #12 on: June 29, 2012, 10:41:17 pm »
Hi Richard,

Yes I followed those instructions and still 3 LED flash. To your second question. The presure is equal on both the high and low side at 35 PSI.

Richard

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #13 on: June 30, 2012, 01:14:54 pm »
I have one test that will confirm or eliminate a failed compressor. I will need to know where in the system  high pressure service port is located?

Compressor can be eliminated by the following:

With a standard three hose gauge set remove center yellow hose and place a self-sealing cap on center hose connection instead of hose.
Now with both gauge valves closed connect red and blue hoses to service ports.
Now open both gauge set hand valves.
Now turn refrigerator power breaker off for one minute to reboot LED circuit.
Now turn on compressor and refrigerant will flow through gauge set freely and no LED signal.
If LED flashes there is mechanical difficulties in compressor or there is blockage coming out of compressor on its way to your high pressure gauge service port.

If there is no flashing of LED close gauge suction valve and suction pressure will drop. It will now be possible to open blue valve slightly if there is blockage elsewhere in system and regulate suction pressure between 10 and 15 psi causing gauge set to cool slightly.

heron

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Re: Correct High/ low pressures for a bd 35/50. No frost on evaperator!
« Reply #14 on: July 10, 2012, 11:10:14 pm »
I was able to perform your test today. 1st resonse: The high pressure port is located 5" from the compressor on the line that goes to the evaporator. This is after the connection to the copper line.

2nd response: I hooked the manifold up to both the high and low ports. I didn't have a cap for the yellow hose, but the yellow center port has a tee and two ports so I connected both ends of the yellow hose on the center ports of the manifold. I then opened the blue and red valves and tuned on the system. The LED flashed three times right away.

From what you are indicating it seems the compressor is siezed.

Question: how do I tell if I have a metric or imperial compressor? Rparts lists both. Does the sticker on the side give any indication?

Is there a way to take the compressor apart and see if it can be made to work.