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Old 18-03-2016, 00:09   #31
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Re: BD35 compressor not making frost on plate .

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Originally Posted by typhoon View Post
Maybe a constant pressure expansion valve instead the fixed orifice?

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Auto filter drier with sight glass sounds like a good idea and I will put one in the unit I am building now.

I am not sure about changing out the capillary tube to an expansion valve. The BD35 does not have much capacity and it might result in an unstable system.

Just about every small system I have seen uses a capillary tube. I think this is particularly important with low powered DC systems as the capillary allows the pressure to equalize across the compressor so that it does not have to start against a pressure lock which would cause the motor to pull very high amps.

I'd stay with the capillary for now, never a good idea to get too many modifications going at once on any dynamic system - too many variables to confuse issues.
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Old 18-03-2016, 06:02   #32
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Re: BD35 compressor not making frost on plate .

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Auto filter drier with sight glass sounds like a good idea and I will put one in the unit I am building now.

I am not sure about changing out the capillary tube to an expansion valve. The BD35 does not have much capacity and it might result in an unstable system.

Just about every small system I have seen uses a capillary tube. I think this is particularly important with low powered DC systems as the capillary allows the pressure to equalize across the compressor so that it does not have to start against a pressure lock which would cause the motor to pull very high amps.

I'd stay with the capillary for now, never a good idea to get too many modifications going at once on any dynamic system - too many variables to confuse issues.
Technautics "Cool Blue" (TEV) and Sea Frost both (CPEV) use an expansion valve with great success. Neither of them use it with a flat rollbond evaporator plate . I wonder why?

I am not going to do anything to this system , just a good evac and recharge , see if I can get it going, just waiting for the Scharder valve for the high side hook up .

The next system for the freezer I may build, As you can tell I love to tinker and understand how things work . Lots of study ahead

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Old 18-03-2016, 06:31   #33
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Re: BD35 compressor not making frost on plate .

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You would not want to alter refrigerant capacity with a receiver filter dryer and sight glass on a capillary tube refrigerant flow control system.
I don't doubt you of course, but don't understand why, will you explain?
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Old 18-03-2016, 07:25   #34
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Re: BD35 compressor not making frost on plate .

I think I understand what Richard is talking about . Found this on the web

Since the pressure on the two sides of the capillary equalizes when the refrigeration plant is stopped, one should not overcharge the system with the refrigerant. Due to this reason the receiver is also not installed in the refrigeration system with the capillary. If the system is overcharged the discharge pressure from the compressor will be high and the compressor would get overloaded. Thus the refrigerant charge in the refrigeration and air conditioning systems with the capillary tube is critical.

Accumulator Used in the Refrigeration Systems with Capillary Tube


Accumulator is a small hollow cylindrical shape vessel made of copper. It is fitted between the evaporator and the compressor of the refrigeration system towards the suction side of the compressor. Sometimes the refrigerant leaving the evaporator carries liquid particles. These particles get separated in the accumulator. The liquid refrigerant collected in the accumulator slowly gets vaporized and is then sucked by the compressor. The accumulator also prevents the flooding of the liquid refrigerant to the compressor when the load on the evaporator drops down drastically.


Seems like a different language and I had to read it a couple of times but I got the drift of it .


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Old 18-03-2016, 08:14   #35
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Re: BD35 compressor not making frost on plate .

Accumulators or Drier/Receivers are used on expansion valve systems...you can see the big one we have with the sight glass on top next to the red high pressure port in the below photo.

Drier/Receiver provides a place for the 24oz of refrigerant to "wait" until the expansion valve calls for it. A capillary orifice system doesn't have a "waiting room" for the refrigerant because there is a critical charge of about 3.5 to 5oz of refrigerant. They are called critical charge systems due to the need for the right balance of charge to match the volume of the refrigerant loop. (IE a fixed set/length of hoses, a Fix/matched size of evaporator) This is one of the key differences in why the condensing unit (radiator) on a system with a TXV can be MUCH larger than one with a capillary orifice. A larger condensing unit, means a higher temperature of operation before you start losing efficiency. (90-degs for the standard AB cold machine)

The units we sell to the US Military for their mobile food carts are rated for 135-degs F all on air cooling, which happens to be the standard CoolBlue compressor. It's why I always laugh when people say you can't use air cooling in the tropics...well you can if you design for it...

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Old 18-03-2016, 08:19   #36
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Re: BD35 compressor not making frost on plate .

So why would a drier be a bad thing, I understand of course refrigerant capacity would increase slightly, but it should work anyway?
Just because I am a pessimistic person I have never trusted systems without driers, I understand they are out there in the millions, but they are intolerant of any particles and or moisture in the system, I suppose on a truly sealed system that is never broken into, but a system that may be serviced, isn't a drier a good piece of insurance?
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Old 18-03-2016, 08:54   #37
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Re: BD35 compressor not making frost on plate .

To not have a filter/drier in a refrigeration system in my opinion is CRAZY just asking for trouble and I won't mention all the fiascos of dead systems of a major manufacturer that didn't include a filter/drier on their keel cooler systems...uggg.

Adding a Filter/drier of appropriate size would be no problem and if I had a refrigeration system without one on my boat, I would add one!

The refrigeration systems are completely closed and sealed systems, unless you get moisture in during the charge process or an inadequate vacuum prior to charge. Or....what if during the build process the solder joints were not done with an adequate nitrogen air purge flowing through the tubes? Those oxidation crystals could work their way loose over the years and plug the system....Or what about the compressor oil becoming overheated and slugging up? Maybe....just maybe that $1 drier receiver would literally save your bacon from spoiling dies your refrigeration system dies "out there", which according to Capt Ron, it when it will always happen.
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Old 18-03-2016, 11:29   #38
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Re: BD35 compressor not making frost on plate .

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Originally Posted by a64pilot View Post
I don't doubt you of course, but don't understand why, will you explain?
All refrigerant systems must have a dryer. My comment was it should not be a dryer receiver with sight glass as was suggested.
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Old 18-03-2016, 11:50   #39
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Re: BD35 compressor not making frost on plate .

64 pilot. Rich posted a refrigeration 101 UTube on an earlier thread you should read.
There are major difference between the design of a system with a capillary tube refrigerant flow and a system with a Thermo Expansion Valve (TXV). The main reason these small Danfoss 12 volt compressor systems use capillary tube expansion devices is costs. The Cap tube system does not require a refrigerant receiver tank or a sight glass or an expensive TXV.

CAP TUBE refrigerant flow control systems
Capillary tube systems: are generally not used in mobile refrigeration because their performance is greatly affected by ambient air temperature and condenser cooling medium temperature changes. When one of these small cap tube systems is serviced correctly in Boston and moved south to Miami the temperature may be degraded because there is too much refrigerant in system. Normally there will be no liquid refrigerant in these cap tube systems when they are not in use when at standard day temperatures only gas vapor is present. When a complete heat soaked small Danfoss system is at 70 to 80 degrees F the static gas vapor pressure in system will not have any refrigerant phase changed to a liquid. In this example when high side pressure exceeds 190 psi liquid mixed with gas vapor will begin to build up against the long cap tube. As refrigerant flows through the long cap tube sub cooling occurs within tube condensing more vapor to liquid as it interiors evaporator coil.
A technician must remember that performance of these Small cap tube BD compressor systems requires correct volume of liquid refrigerant to within 15 grams of correct amount and reasonable control over condenser cooling medium’s temperature range.
Other than lower hardware costs why are capillary tube flow control devices used instead of the TXV flow control systems? A. The job shops that assemble icebox refrigeration units rarely manufacture the thin plate evaporators and companies that do include cap tube properly sized with each evaporator.
TXV refrigerant flow control systems
• The objective of any refrigerant control device is to cause refrigerant process of absorbing heat to occur in the evaporator. Thermo Expansion Valves are used where a wide variation of temperature range is needed. Because of extra refrigerant storage in a receiver required for TXV flow control it allows for variations in refrigerant charge without impacting performance. The receiver also helps separate vapor from liquid to insure there will always be a liquid head pressure at TXV. Instead of allowing pressure by itself as in a cap tube system to control flow the TXV compares temperature across evaporator to control refrigerant flow.
Mother Nature has laws on refrigerant that when broken can provide disastrous results to performance and even a systems service life. An accurate history of a unit will generally pin point poor performance or need for complete system replacement. Below is a list of risky practices that have caused systems to self destruct:
• Use of unapproved refrigerants.
• Connecting gauges to a small system or tampering in any way without confirming first refrigerant or its flow is a problem by non destructive means.
• Mixing any compressor oil with manufacturer’s original oil.
• Adding Stop leak, Dye, or any additive to refrigerant.
• Allowing compressor to operate at excessive temperatures in warm climates especially incorrectly installed air cooled units and some water cooled units without separate compressor cooling.
• DIY systems sometimes use low pressure side tubing including evaporator coil inside holding plates that is larger than compressor’s return vapor line. Over time with low suction line velocity oil will be trapped causing loss lubrication at compressor.
• Adding refrigerant to achieve frost on evaporator when amperage, low pressure and high pressure are all in proper range will only compound trouble over time by overheating compressor oil.
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Old 18-03-2016, 12:04   #40
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Re: BD35 compressor not making frost on plate .

OK got it, with no way of holding excess refrigerant you have to have amount correct plus or minus a very small amount, I can see why pressure gauges and charging to pressures may not be a good plan with these little units, and they would at first glance seem to be doomed, with no or almost no tolerance in charge, it's a matter of time before charge will be low, measured in years maybe, but it is an eventuality?
Seemingly then the only real course of action in that case is to pull a hard vacuum, hold it for a decent amount of time and put in the exact charge by weight, but if it's a DIY system, how is that exact weight of charge determined?
It's that or the hit and miss method of adding a tiny amount and waiting and observe frost line?

I understand expansion valves as that is where my experience base is, and not having a receiver, an accumulator if you will that can hold a little excess liquid refrigerant to act as a buffer is irresponsible it seems for a thousands of dollars mobile system?

I understand it, and it's logical for say the $100 ice maker I bought, it was only $100, at that price point, I get it, but not at a higher price point.

My opinion only.
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Old 18-03-2016, 12:12   #41
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Re: BD35 compressor not making frost on plate .

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Thanks for all the replies. I have removed most of the gas and am about to refill . Don't think I will have to vacuum I didn't open any thing . How many onces do these things take to get me close ? My evaporate plate is a good size 32x16

Rdgards
Why did you dump the charge?

Just fill slowly and watch for frost creep on the evaporator.

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Old 18-03-2016, 12:13   #42
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Re: BD35 compressor not making frost on plate .

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Thanks for all the replies. I have removed most of the gas and am about to refill . Don't think I will have to vacuum I didn't open any thing . How many onces do these things take to get me close ? My evaporate plate is a good size 32x16

Rdgards
Why did you dump the charge?

Just fill slowly and watch for frost creep on the evaporator.

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Old 18-03-2016, 12:27   #43
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Re: BD35 compressor not making frost on plate .

Ok all this has given me reason to rethink. I have my system out and on my bench at work, the compressor has very little use and is essentially new. I just bought the new evaporator plate , and it is new from Nova Kool . Think I will play a bit with it and put a bigger condenser on go to a TXV system with a large receiver drier like Rich's "Cool Blue" system .
The evaporator plate has 23 feet of piping so now need to educate myself on the valve and orifice combination , also a MOP valve ?

Going to practice my soldering and make sure we have a bottle of nitrogen in the shop.

Back to the books.

I will keep you posted with the progress.

Thank goodness for this forum

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Old 18-03-2016, 12:31   #44
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Re: BD35 compressor not making frost on plate .

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Why did you dump the charge?

Just fill slowly and watch for frost creep on the evaporator.

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It was brought to my attention that the gas shipped in the new evap plate may not have been refrigerant , may have been nitrogen ?

Doesn't matter now, I have decide to engineer the system any way. I guess R parts will be my best friends for a while

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Old 18-03-2016, 15:00   #45
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Re: BD35 compressor not making frost on plate .

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I just bought the new evaporator plate , and it is new from Nova Kool . Think I will play a bit with it and put a bigger condenser on go to a TXV system with a large receiver drier
Ah....Hold on a minute there Tex, one of your cattle may have slipped the fence....

Have you ever seen one of those kid books where an animal is made up of three different pages that can individually turn to create different composite animals? You can have a Lion's head, zebra body, and Alligator tail? The animal looks cute, but what isn't mentioned in the book is that the animal would die out in the real world because it's body design isn't optimized for it's particular nitch environment any longer.

So rather than finish changing out all the three heat exchanger and all the hoses on my Lehman 120Hp motor, I'm rattling on with children stories trying to warn you gently about making a Frankenstein Refrigeration system.

The critical orifice on your white aluminum evaporator is typically set inside the evaporator itself and not something you can change. The critical orifice is matched for the side of the evaporator and can't just be swapped out with a TXV. Take a look at your evaporator and follow the inlet plumbing line into it. Do you see those three smashed lines at the inlet? Those are there to set the orifice/flow on most evaporators. Now maybe you have a different type with an external critical orifice...but you don't want to find that out after you chopped this up and have the Alligator turn around and bite the Lions head.
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