Author Topic: Archive 5  (Read 4004 times)

Richard

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Archive 5
« on: May 03, 2012, 10:38:08 am »









Spillover    Archive 5
Answer to question about a hole size for spillover air return through divider, it must be slightly larger than the fans capacity to prevent air pressure from leaking through lid seal. A one inch square muffin fan, need at least a one inch square hole. A one inch round fan that fits in a round hole still needs a square one inch hole. Spillover in a refrigerated box means to allow air or energy, that has much of its heat energy remove from it, to leak into another area of the box. The rate that spillover leaks from one area to another will determine the temperature difference between the two areas. In a conventional top loading boat ice box conversion refrigerator it is the thickness of the divider separating the areas that has the largest effect on minimum spillover. If there is only a need for a fifteen degree temperature difference between the two areas then a inch solid divider with no air circulation between the two is required. For a thirty to forty degree difference in temperature (Delta T) the divider needs to be one and one half to two inches thick. A boats top loading box with its side by side freezer refrigerator is much like a side by side home refrigerator, except air in both boxes on a boat have almost no room to naturally tumble warm air up and cold air down. In 1983 my boat box conversion designs determined box temperature difference by divider thickness. Next changes in box Delta T control were many holes and corks in divider with some companies offering the home refrigerator/freezer thermostat door. These natural air transfer devices produce less than desirable results unless boxes where almost empty. Todays more efficient temperature spillover systems both in the home and on a boat incorporate a spillover fan with a thermostat to control refrigerator section temperature. On boxes smaller than eight cubic feet a one inch 12 volt fan of approximately 10 cfm is mounted mid way down the divider. The air drawn from freezer must have an opening at the top of divider large enough to return air forced through the refrigerated box after it has picked up heat.


Thanks to both responders. I will have 2" of insulation between the two boxes. There will be a one inch square hole half way down, using a thermostat controlled fan. I will put a one inch square hole at the top between the 2 boxes as recommended. [u:13f2418396]Many[/u:13f2418396] hours of research are finally resulting in a plan. I'm finding the devil is in the details of how exactly to implement the guidelines I have learned. Hense I find myself running into the dumb little questions like the above. So thanks again.

Thin plates
A thin stainless steel evaporator would be the preferred plate if it were capable of matching the capacity of the condensing/compressor unit. Thin one piece stainless plates were common years ago but no longer are they available. The problem with the stainless plates offered today is the overall rate of heat transfer from refrigerant to the air/product in a box, is not as efficient as a stamped or roll bond evaporator would be. If you select two stainless plates with a lot of surface area that at least matches the largest single aluminum thin plate sold for that compressor capacity, the system should be in balance.

Running the copper tubing
This is our most recent stumbling block in our refrigeration rebuild project. (I will hopefully run out of stupid questions soon. :wink: ) We are stymied by lack of easy access to the walls of the freezer cabinetry for running the copper tubing into it. The compressor will be located beneath the floor where the wood cabinet containing the freezer box will be built. Because we are blocked from entering the wood cabinet from outside of the [u:cdb9a17cef]sides[/u:cdb9a17cef] of the cabinet, the solution seemed to be to come up through the floor, just inside the wood cabinet and at the outer edge of the insulation, run straight up to the height of the top of the freezer box, then angle over to enter the freezer box. However the problem with this is that the tubing would then be entombed inside the wood cabinet once the top is put on, making it nearly impossible to access the tubing if it ever had to be removed or replaced. It occured to me to build a raceway out of pvc pipe that would be fitted where the tubing would be run, (to be sealed well at both ends after the tubing is run), so that the tubing could be pulled out if that was ever required. So my question is, will the tubing flex enough to be snaked through a 90 degree turn in a 1.5" ID pipe? I read that the tubing is quite flexible, but since I have never personally handled it, I don't know if it will do this. Once again, thanks in advance for your kind assistance.

Refrigerant tubing
If you are installing a pre charged system there will be disconnects at the end of lines that need a larger hole than the line itself. One forth inch tubing can be pulled through a blind area as long as the bend radius is large enough with no sharp corners, say an eight inch radius.


Thanks so much, as always. It looks like the tubing would not be able to make the 90 degree angle then. The product instructions specify a 1.5" opening required to accomodate the disconnects at the ends of the lines, so I was planning a 1.5" diameter raceway. Well, back to the drawing board. This issue is creating a bit of a challenge. As I said elsewhere, the devil truly is in the details. :(

Uline compressor Start-up
I have a Uline ice maker that occasionally would draw alot of amps and kick the circuit breaker upon initial start up. It now is doing it every time. There appears to be a relay that plugs into the compressor where all the power wires go to. Could this relay be bad or is the compressor shot? The unit is original on a 1992 Carver but used rarely. Any help would be appreciated. If it is the relay where can you get them Uline hasn't been any help.

Ice Maker Trips Breaker
I am assuming that the breaker that trips is at the boats electrical panel and that this is an AC compressor and not a 12 volt unit. If the breaker is rated at only five amps and it has been used as a switch to turn the unit off an on I would check it first. The small relay that plugs into compressor is used to start compressor them it switches to run motor windings. The relay, capacitor if it has one, can be bad or the windings in compressor motor are shorted out. You can buy at a local appliance parts store a Relay/Overload Combination unit for about $12 that will replace the relay. Again without having all the information I am assuming this is a small ice maker, in that case the part to buy would be labeled, For Any Hermetic Compressor unit 1/12 thru 1/5 H.P. If the unit has a capacitor then the unit needed would be a Three In One ( Relay, Overload, and Start capacitor). If the problem is not the Breaker, Boat wiring or Relay them it will be a bad compressor.

Uline compressor start up
Thank you, It is a small ice maker. Does the relay that plugs into the unit contain the capacitor or is it separate? I see wires,Black coming from the on/off switch, the fan and the ice maker tray to the relay as well as one red wire to a different post. The relay has three prongs that plug into the compressor. I assume If the capacitor is not built into the relay it should be visible near the compressor. Or can it be iside of the compressor? Thanks for your help. Brad

Hard starting compressor
Very small compressors do not have start compacitors, if it does it is about one inch in diameter and at least two inches long clamped to the compressor. Do not disconnect any wires until you recieve the new part then follow directions on package, it installs in secounds.

Old coldmachine problem
I don't know the age of my Coldmachine, but the boat is a 1980. This unit has been working quite well for the 6 years or so I've owned the boat. Recently I find that after it has been running fine for some number of hours with the evaporator frosting up just like it should, it quits cooling. The compressor continually tires to start every minute or less while the fan continues to run. I would guess the compressor run is 1-2 seconds before shutting down. At first I could turn the unit off for a time after which it would restart. I have actually heard it run slightly longer with each attempt and then finally stay on, but eventually the same problems repeats. The voltage at the unit was 13.25 and sagged very little as the compressor tried to start ... high 12's at least. I have not measured the amperage draw. The fan is now my suspect from other discussions on this forum. It is an aluminum blade fan and is actually slightly hard to turn by hand when off. Any other thoughts or suggestions would be appreciated.

Compressor Start Problem
First step is to make sure that there is good air flow through condenser and it is not clogged with dust. I am assuming that this is a Danfoss compressor and not a brush type DC compressor. That old fan may be your problem. The following is from my 12/24 volt book. Danfoss BD 2.5 and BD 3 compressors failure to start. Repeated failure of start and a audible cycle beep is caused by a program in the electronic unit. It is programmed to stop the compressor if; #1. The voltage is below 11.5 volts during start . Check batteries for charge. Check for a resistance connection. The best and quickest way to do this is run a temporary set of wires from a fully charged battery to the compressor electrical module. The wire size and polarity is important. A voltmeter reading will not read fast enough to identify a voltage spike. #2. The fan or if water-cooled, the pump relay is drawing more than one amp.. To check disconnect one of the wires to fan. If the compressor starts OK replace fan. #3. The compressor is going bad and drawing more than 7 1/2 amps. To check install an ammeter in the power wire to the refrigeration unit. It should draw 5 to 6 amps when running, if more than 7 amps, the compressor is about to fail. To do this test the unit must be running. It is sometimes possible with a failed compressor to see a quick movement of the ammeter to 10 amps. or higher. The best test to determine condition of the compressor field windings is to check their resistance with an ohmmeter, See Drawing. #4 It is a good idea to eliminate the thermostat as a cause while checking the system. To eliminate the thermostat and its wiring disconnect its wires from the electrical module. Place a place a jumper wire across the module thermostat terminals. #4. If the above checks do not determine the cause the electrical module is defective. WARNING, do not install a new module on a compressor that test bad with the ohm meter.

Ice Maker for small boats
The new Mr. Freeze small ice maker sold at Target for $250 is also available at Casco for $150. This looks like a good unit for a boat. Portable machine makes a tray of ice in just 10 minutes and up to 35 lbs. in a day Features 3 cube-size settings, touch-pad controls and a 1-gal. water reservoir Includes ice tray and scoop UL listed 17-1/2Hx15Wx17-1/2L"


Richard, Do you have some reccomended sources for SS evaporator plates? How about roll-bond? What I have found so far are roll-bond plates which use cap tubes. It is my intention to build a system with 2 zones and, from what I have read, using cap tubes in this environment will be quite difficult in balancing out the system. Regards,

Evaporators
Both Sea Frost and Frigoboat sell Stainless Steel evaporators. Sea Frost advertises special order custom plates.

bd35 charge pressures
I am replacing a bd2.5 compressoor with a new Danfoss bd35. The system is water cooled, with a small evaporator box. I have flushed the old lines and evacuated the system. Can you tell me what the approximate charge pressures should be on the high and low sides? Thanks for your help

Servicing a BD35 compressor
I am traveling this week and do not have my 12 volt book or a detailed check list with me but here is a shrot version of servicing a BD35 system. After vacuuming be sure to purge yellow hose with 134a. With the compressor off, Add 134a refrigerant as a gas until the pressure is about 50psi. The box interior and system should be warm, preferred 70 to 80 degrees F. Start compressor and wait till pressure drops to its lowest point, this takes about five minutes. For 134a and a small evaporator the correct suction pressure for your system warm is 6 to 8 psi. This means that refrigerant level can only be adjusted in the first 15 minutes with a warm plate because as it cools suction pressure will drop. If it can not be set correctly in fifteen minutes let system warm up and start it up again. The high pressure readings will reflect only the efficiency of condenser's cooling and unless you have a way to control the water cooling it is of no use. High pressure is normally above 100 and less than 130 and will reduce as the box cooles. It is not possible on this compressor to have the refrigerant charge correct for different water temperatures so it may be necessary to readjust it if cruising location changes. See FAQ 33 on my web site for more info on this The indication that refrigerant level on an operating system is incorrect will be visible by the frost line. Frost on the return line means, too much refrigerant, and loss of refrigerant covering 100% of evaporator indicates low refrigerant charge. Slightly low on refrigerant is more efficient than too much refrigerant.

Cycle timing for refridgerator
I recently had the evaporator plate replaced on my A/B cold machine due to a leak. The system was completely vaccumed and refridgerant added and unit has been running OK. This unit is installed on a Hunter passage 420 with a freezer, spill over and refirgerator. I noticed today that the unit was running for close to 3 hours before it shut off. Once it shut off it stayed off for an hour and half before cycling again. During the day the unit has been cycling on and off at varying intervals. Tonight it came on a 1745 and just shut down at 2045. In each case the spill over has run the entire time. Within minutes of spill over being satisified the compressor shuts down. Does this seem normal?

Adler Barbour Cycling
Danfoss compressor cycle time will depend on the type A/B configuration you have. If the only change was replace the evaporator then I would question the refrigerant quality or volume added, frost should not be present on return line to compressor. Do you know the current amperage draw of unit? If the system has their Power Plate which is a low capacity holding plate, cycle time may take longer than one hour. If there is good airflow through the condenser and frost is present covering 100% of the thin plate evaporator cycling should accrue at least once or more times per hour. It is the surface temperature of the evaporator or power plate that the thermostat monitors. There is a chance that thermostat is sticking and causing compressor to run longer than necessary, if this is what is happening the box will be getting colder than normal.

Adler Barbour cycling
Thank you for your reply. The amp draw is 5.1 which I understand ins in the normal range. There is not a Power Plate on the unit, it is just a plain thin evaporator plate. in the past the cycling time was about 20 minutes on and 20 minutes off. The surface of the plate is completely frosted and the system was runing for about a week at the normal cycle pattern. The box is not getting colder than normal with this long cycle. I have a digital thermostat on the spill over and what seem to be going on is that the compressor is in this long run as it is taking the refridge from 41 to 37. I will have the refrigerant check.

AB Performance
I do not recommend having the refrigerant checked if frost levels and amperage is in the ball park as listed earlier. Amperage of 5.1 to 5.4 would be about right if it has the large evaporator bin.. Are you sure the condenser coil is clean and not filled with dust? What refrigerant was put back in compressor? What is the compressor model number?

AB Perfotmance
I have not had the refrigerant checked as the system started running correctly by itself.....about 20 to 25 minutes on and off and has for the past 24+ hours. The condensor coil was completely with air and vaccum. Refrigerant used was 134a and the model is an A/B CU-100 Cold Machine. The mystery remains as to why after a week the unit went on its extending running cycle and than reverted to its normal cycle.