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Old 12-10-2012, 08:29 PM   #1
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Recharging Danfos compressors

I have intentionally, and fairly stalwartly, maintained ignorance about refrigeration systems. Now, however, I have to recharge my Danfos BD-35 compressor as it no longer gets the plate cold enough. I purchased r134a in a very nice canister with a pressure gauge, and have absolutely no idea what to do next. The unit has a suction ("C" in diagram), process ("D") and discharge ("E") connector, and the canister I bought would allow me to connect it to anyone of these. I have a suspicion that there may actually be one of them that is correct. Anyone know how to recharge my system? Thanks in advance!
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Old 12-10-2012, 10:00 PM   #2
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Me, I think the prudent move would be to find a guy to do it for you....
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Old 12-10-2012, 10:03 PM   #3
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Don't get any air in the system, purge the fill line before tightening the connectin to the compressor. Charge it through the suction (low pressure side) while it is running. Charge gas(little can upright) not liquid (can upside down) and only add very little, check operation, then add more if necessary.

Be careful, the can is under a lot of pressure, contains refrigerant oil, and if you get a dose in your eyes it can do a lot of damage in a heartbeat. Be very careful.
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Old 12-10-2012, 10:18 PM   #4
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Don't get any air in the system, purge the fill line before tightening the connectin to the compressor. Charge it through the suction (low pressure side) while it is running. Charge gas(little can upright) not liquid (can upside down) and only add very little, check operation, then add more if necessary.

Be careful, the can is under a lot of pressure, contains refrigerant oil, and if you get a dose in your eyes it can do a lot of damage in a heartbeat. Be very careful.
I can track with most of that, but when you say "purge the fill line", how is that done? I assume you are talking about the "C" connection - suction. What pressure should I be looking for? What heck are the discharge and process connections for? Why am I doing this? Why do fools fall in love?
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Old 12-10-2012, 10:21 PM   #5
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From my Danfoss page at the little DeFever website -

1. Google Richard Khollman, visit his website, read his FAQ, and buy his book on small marine refrigeration systems. Feel free to post questions on his forum. I believe he knows more about this subject than any man alive.


2. If your system has not leaked, or worse been overfilled, then any problem you might have is most likely related to DC supply voltage, or a overheated/failed control module. Learn how to connect a fault indicating LED to the module and what the flashing code means. Install a muffin fan to cool the control module.


3. If you hire a technician to work on your Danfoss based system the first question you should ask is "What's the amount of refrigerant in the system"? If he doesn't have a clue then he is not qualified to work on a Danfoss/capillary tube system. Just putting gauges on these small systems can alter the amount of refrigerant.


A refrigeration and AC technician may be very skilled working on larger expansion valve systems and not skilled on small capillary tube systems.

Mike
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Old 12-10-2012, 11:13 PM   #6
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From my Danfoss page at the little DeFever website -

1. Google Richard Khollman, visit his website, read his FAQ, and buy his book on small marine refrigeration systems. Feel free to post questions on his forum. I believe he knows more about this subject than any man alive.


2. If your system has not leaked, or worse been overfilled, then any problem you might have is most likely related to DC supply voltage, or a overheated/failed control module. Learn how to connect a fault indicating LED to the module and what the flashing code means. Install a muffin fan to cool the control module.


3. If you hire a technician to work on your Danfoss based system the first question you should ask is "What's the amount of refrigerant in the system"? If he doesn't have a clue then he is not qualified to work on a Danfoss/capillary tube system. Just putting gauges on these small systems can alter the amount of refrigerant.


A refrigeration and AC technician may be very skilled working on larger expansion valve systems and not skilled on small capillary tube systems.

Mike
Thanks Mike. I doubt it is a voltage issue, but maybe. Unfortunately, even though Anacortes Washington has many marine services, we don't seem to have a marine refrigeration expert nearby. I will check out Richard Kollman's site, thank you.
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Old 12-10-2012, 11:55 PM   #7
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Logic (not knowledge) tells me if you need to re-gas, your gas has gone somewhere(? undesirably, into the atmosphere). I don`t think it wears out or naturally diminishes. That suggests you have a leak to find and fix before you add gas which would otherwise follow the last lot. I think refrigeration guys sometimes use a dye to help find leaks.
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Old 12-11-2012, 05:53 AM   #8
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HIRE someone.

Mike is right , the problem is the small systems run on almost spoonfuls of refrigerant.

To get it right the tech must remove all the gas , then add a tiny weight of gas , by DA Book.

He must use a very accurate scale . Too much or too little and it wont work.

Old systems could be overfilled , seldom with a problem , but these can not ..
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Old 12-11-2012, 06:08 AM   #9
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+1 on Khollman

Also, check for dust and lint between between the fan and the condenser. If there is a lot of dust/dirt/lint, it can reduce the efficiency to the point that you can have a false indication that the system needs recharging.
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Old 12-11-2012, 07:26 AM   #10
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If your system has not leaked, or worse been overfilled, then any problem you might have is most likely related to DC supply voltage, or a overheated/failed control module.
Or the compressor could simply be worn out. There is nothing wrong with an owner putting a bit of gas in the system to see if it returns to normal operation. If it does then he can choose for himself how to proceed. If not then at least he learned that lack of refrigerant may not be the problem.


Quote:
If you hire a technician to work on your Danfoss based system the first question you should ask is "What's the amount of refrigerant in the system"? If he doesn't have a clue then he is not qualified to work on a Danfoss/capillary tube system.
A skilled technician will say "let me take a look" and read the dataplate that tells what kind of refrigerant and the weight of the charge.


Quote:
A refrigeration and AC technician may be very skilled working on larger expansion valve systems and not skilled on small capillary tube systems.
A skilled technician will certainly know the difference between capillary units and TXV systems. It is pretty much one of the fundamentals of the guy's craft.
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Old 12-11-2012, 07:34 AM   #11
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I can track with most of that, but when you say "purge the fill line", how is that done? I assume you are talking about the "C" connection - suction. What pressure should I be looking for? What heck are the discharge and process connections for? Why do fools fall in love?
These are Schrader valve connections, right?

Put gas in the one labeled suction or low pressure.

You don't have gauges so don't worry about the pressure. It varies with temperature anyway and whether the unit is running and you have to know what it means which I suspect you may not so don't freak out about it despite all the expert advice flying around.

Before you tighten the connection to the suction fitting on the compressor, crack the valve on your little can just enough to hear a hiss at the compressor. That gets rid of the air in the tube between the two.

With the unit running, give it a quick shot of gas and feel the evaporator coil to see if it is getting colder. If it is give it another quick shot and let it run for a while. If the performance is good, disconnect and see how long it lasts. If nothing changes then you have other problems and can choose for yourself how to handle it.

[QUOTE] Why am I doing this? {/QUOTE]

Because you want to learn something about fixing your own boat problems, and it feels good to be a bit more self-sufficient, it might save money, and you will be impressed to no end with your new found skills and confidence. As long as you are careful and do a bit of reading beforehand there isn't much of a downside despite what you might read here.

Good luck and be careful.
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Old 12-11-2012, 09:23 AM   #12
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Logic (not knowledge) tells me if you need to re-gas, your gas has gone somewhere(? undesirably, into the atmosphere). I don`t think it wears out or naturally diminishes. That suggests you have a leak to find and fix before you add gas which would otherwise follow the last lot. I think refrigeration guys sometimes use a dye to help find leaks.
It's been five years, so Rick's suggestion that it may just be a failing compressor could be the simplest solution, especially since it just started a couple of weeks ago.
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Old 12-11-2012, 09:24 AM   #13
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+1 on Khollman

Also, check for dust and lint between between the fan and the condenser. If there is a lot of dust/dirt/lint, it can reduce the efficiency to the point that you can have a false indication that the system needs recharging.
No, it's quite clean, and the fan turns at the normal speed.
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Old 12-11-2012, 09:26 AM   #14
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[QUOTE=RickB;118865]These are Schrader valve connections, right?

Put gas in the one labeled suction or low pressure.

You don't have gauges so don't worry about the pressure. It varies with temperature anyway and whether the unit is running and you have to know what it means which I suspect you may not so don't freak out about it despite all the expert advice flying around.

Before you tighten the connection to the suction fitting on the compressor, crack the valve on your little can just enough to hear a hiss at the compressor. That gets rid of the air in the tube between the two.

With the unit running, give it a quick shot of gas and feel the evaporator coil to see if it is getting colder. If it is give it another quick shot and let it run for a while. If the performance is good, disconnect and see how long it lasts. If nothing changes then you have other problems and can choose for yourself how to handle it.

Quote:
Why am I doing this? {/QUOTE]

Because you want to learn something about fixing your own boat problems, and it feels good to be a bit more self-sufficient, it might save money, and you will be impressed to no end with your new found skills and confidence. As long as you are careful and do a bit of reading beforehand there isn't much of a downside despite what you might read here.

Good luck and be careful.
Thanks Rick, I'll give it a shot and report back. The gas I bought does have a gauge on it, and while I can probably find the pressure in the specs, do you know the range I should target? Finally, I take it that I don't need to crack the discharge port, just pressurize the suction side a bit? Do you know what the process port is used for? Initial setup?
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Old 12-11-2012, 11:49 AM   #15
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Originally Posted by Delfin View Post
The gas I bought does have a gauge on it, and while I can probably find the pressure in the specs, do you know the range I should target? Finally, I take it that I don't need to crack the discharge port, just pressurize the suction side a bit? Do you know what the process port is used for? Initial setup?
Don't mess with the discharge port, it is for connecting the high pressure gauge.

The process port is sort of a suction port, it is used for filling the charge during the production process ... the guy on the production line connects the charge supply there rather than passing it through the compressor itself as you are going to do with it running.

As far as what pressure to look for, as I wrote, it depends on the ambient temperature and the refrigerant. I assume it is R134, correct?

With the unit off and at ambient temperature (don't do this after it has run because it will be warm and you won't really be able to measure the internal temperature very well) match the temperature with this chart/calculator and see if the pressure matches the temperature:

R134a Refrigerant Pressure Temperature Calculator

Keep in mind that little gauge is not lab quality so the reading you get might be off but all that will really tell you is if there is still liquid refrigerant in the system or if it has all leaked out. If there is liquid, the pressure/temperature will match. If there is no liquid, the pressure will be lower than it should be and you know you have a larger leak or it has been going on for a long time. As long as there is some pressure you shouldn't have to worry about air in the system or needing to pull a vacuum and can probably get away with adding refrigerant from your little can.

If the unit is really low, invert the can and give it a quick shot of liquid ... not much though, just a second then turn back upright. This will get more refrigerant in quickly and should not "slug" the compressor because it will flash into vapor immediately in the low pressure.Repeat as necessary until you feel the evaporator getting nice and cold.

You are performing "shade tree" service here but I believe you will achieve some level of success and find out if the machine has a leak or is worn out or has other problems. It is inexpensive trouble shooting anyway.

Again, be careful with refrigerants, they can hurt you.
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Old 12-11-2012, 12:37 PM   #16
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Many thanks Rick. Makes sense and this will determine whether it is refrigerant or the compressor.
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Old 12-11-2012, 03:53 PM   #17
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Rick B wrote -

“A skilled technician will certainly know the difference between capillary units and TXV systems. It is pretty much one of the fundamentals of the guy's craft.”

That has not been my experience in dealing with Danfoss systems in the past 15 years. General marine refer/ac techs will almost always overfill the system. Kohllman says on his website that his most common service call is to let out refrigerant after a Danfoss unit has been overfilled by a marine A/C tech.

It may be that in an area like FT. Lauderdale you can find a specialists, but in many areas you can not.

Never seen a Danfoss based system with a capacity plate on it. Every Danfoss label I have seen is limited to model number, serial, and refrigerant type. I think that many companies that build Danfoss based systems just don’t bother to put them on. Some system builders do list the capacity, in grams, on their web sites for their most common compressor and evaporator combinations.


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Old 12-11-2012, 05:12 PM   #18
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Never seen a Danfoss based system with a capacity plate on it. Every Danfoss label I have seen is limited to model number, serial, and refrigerant type.
There is no reason to put the charge weight on the compressor, the charge depends on the system size.

The fridge should have a dataplate that lists the type and weight of the charge. For a typical small boat fridge with that compressor I would guess about 5 or 6 ounces but it will be on the machine or in its manual someplace on the specifications page.

Reefer techs are like any others, you can get a diamond or a lump of coal.
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Old 12-11-2012, 05:52 PM   #19
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Check YouTube, there is at least one video of recharging a Danfoss system. I'm sure the advice you've got from Rick is spot on but it may be beneficial to see someone go through the motions prior to your attempt.
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Old 12-11-2012, 06:21 PM   #20
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If you decide to have someone look at it, call David Lehmann at Sea Freeze in Bellingham. His cell phone number is 360-305-9573. He does nothing but marine refrigeration and comes to Anacortes one day a week. I have had him do repairs on my cold plate system. Good luck
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