Fridge suddenly stopped!

[TOM]

Richard, the engine driven seawater condenser is been cooled by the motors water pump I replaced the water pump impeller, started the motor and ran a full check on water flow thru the condensor, there is no problem with water flow if there was my motor would be overheating as the raw water pumps thru the condensor then back up to the motors heat exchanger. I have noticed that the sight glass is showing multiple bubbles when i start the compressor up until the pressure switch cuts in .This from what i have read indicates low refrigerant,but would this cause the overheating problem? .Do i need to get the system topped up? .Would appreciate if you could advise the next step.

[Richard Kollmann]

Tom, you are correct when engine drive refrigerator condenser is in series with water for engine cooling the engine would overheat if water flow was restricted. Many engine driven systems use a seawater bypass that allows some sea water to bypass condenser. Some systems in your country also use suction pressure regulators that restrict refrigerant flow. We still have not confirmed whether the pressure problem is related to poor condenser cooling, as you can not identify condenser, or refrigerant blockage. If we could eliminate these items as the cause of pressure switch tripping we could test pressure switch with a jumper wire. I can not identify the manufacture of your dual pressure switch. The switches I have used only trip when pressure is too high to prevent explosive damage The best thing to do now is to find someone with a dual pressure gauge set and knows how to use them to test both pressures just before pressure switch trips.

[mayball]

Tom, The black tank in the picture looks like an accumulator which has a heat exchanger coil in it. It would get hot when the condenser is not releasing the heat of compression (pump failure or blocked water flow). The "black dome shaped canister alost identical but just a bit smaller" is the receiver and it also would get hot for the same reason. Were you aware of water going overboard from a thru hull a few inches above the waterline when the refrigerator was function correctly? If so, and if there is less or no flow now, your problem, as Richard said, is surely due to restricted water flow.
Don

[mayball]

OOPS Sorry Tom, You and Richard already covered what I had to contribute ( I missed the second page and forgot yours is engine driver).
Don

[TOM]

Hi Don, everything would point to a water blockage but this is not the case as the seawater condensor is getting plenty of water .Thanks for pointing out what the black dome shaped things were they were confusing me . Looks like i will have to get a mechanic out but i have certainly learnt alot about refrigeration!

[mayball]

Hi Tom,
I am working on a system that is almost exactly the same as yours. It is engine driven with both an accumulator and a receiver, however, a sight glass was never installed. The problem with this system is that it would cool normally when started with a warm box. However , the cold plate would not fully freeze. Then when the system was started again with a partially cooled plate, the plate would acually appear to warm up. I attached pressure gages to the system and found that, after running normally initially, the suction would pull into a deep vacuum (about 20 " Hg). I determined that this was a symptom of water in the refrigerant. When the plate was cold, the expansion valve would cut back and the water would freeze in the expansion valve, stopping flow and causing the compressor to pull a vacuum.
I worked on the system today and installed a sight glass and filter/dryer, vacuumed the system to remove the water and air, and pressurized the system with R-12. Tomorrow, I hope to continue charging the system until the new sight glass is full. I have found that neither the high pressure switch or the low pressure switch is connected, so I need to connect them and a timer switch, which is installed but not connected.
None of the problems I experienced involved high pressure due to insufficient cooling such as you have. However, I have some experience with air conditioning systems which overpressure due to a long grassy algae growing in the condenser and cutting down on the heat transfer. This can happen especially in marinas here in Mexico, where the water is stagnate and warm. The strainer does not stop the growth and I can see where it might affect the refer condenser but not affect the engine cooling. The problem was solved by filling the strainer with muratic acid and running it through the system to kill and clean out the algae. However, as Richard said, I would check the pressures first before assuming that the algae is your problem.
Don

[chala]

MAYBALL
Keep an eye on the high pressure refrigeration gauge when recharging, some time the sight glass can fool you.

[Richard Kollmann]

Mayball, Tom’s problem is he has a hybrid system with dual compressors and can not identify engine drive condenser that is needed to check it for excessive heat build up.

Tom, a couple of tips on your problem:

A simple test to determine moisture freeze up in refrigerator expansion valve is to place a wet hot rag on valve. Moisture in valve freezes and thaws repeatedly resulting in a 33 degree F evaporator/holding plate temperature. When hot wet rag comes in contact with valve ice melts and valve quickly freezes rag to valve. Rapid refrigerant flow will hold rag to valve until water in valve freezes again then rag falls free.

With an inoperative high pressure switch it is a good idea to add refrigerant until there is activity in sight glass and then stop adding. Once holding plates are frozen solid it then is safe to add refrigerant to fill sight glass. It is a mistake to operate any engine driven refrigeration system without a functional high pressure switch as it can self-destruct if seawater cooling is inefficient. Tom's system is currently being protected by a high pressure switch trip.

[mayball]

I have completed the work on the Mexico system which is similar to Tom's: The thermostat, low pressure cut-out and high pressure cut-out have been wired in series with the compressor clutch, and the the system has been fully charged with R-12. After the vacuuming of the system to 230 microns, there was no reoccurance of the freezing in the expansion valve. However, a new problem has surfaced. The lowest I could get the superheat at the expansion valve was 30 degrees F with the valve adjusted to the most open setting. I am guessing this indicates that the valve (or the orifice there-in) is too small. This means that even with the valve wide open it cannot pass enough refrigerant to utilize the entire coil in the holding plate. Unless someone can suggest some further checks to make, I guess I will go shopping for a larger expansion valve. It is very difficult to read the info on the top of the existing valve but I think it is a Sporlan F series valve with a 3/8" inlet and 1/2" outlet.
Don

[Richard Kollmann]

mayball, So much for super heat on a holding plate system, low side suction pressure is the real indicator of system performance on this one of a kind system. If you can find one of my DIY books it covers fine tuning of similar engine driven systems, if not here is a general idea of what to expect during a test run. On a warm start up with holding plates warm and clutch engaged suction pressure will drop from a high pressure equal of about plate temperature down to a wide open TXV orifice capicity. Refrigerant flow at full open orifice will vary depending on size TXV used . A single TXV with R12 refrigerant after start will stabilize at a pressure range of from 8 to 20 psi. A couple minutes into the run frost may appear on line returning to compressor. As the plate cools the TXV will begin to reduce suction pressure and return line frost will withdraw. If compressor runs long enough and suction pressure drops slowly evaporator coil inside plate could reach minus 20 degrees F. If suction pressure drops too quickly there is a refrigerant flow problem caused by:
· Not enough refrigerant in system
· Plugged TXV inlet screen.
· Controling gas in TXV sense tube leaked out.
· A restriction somewhere in system
· Superheat adjusting screw turned to restrict flow
· Wrong gas pressure TXV valve installed

[Therapy]

I guess I am confused now.
We are getting troubleshooting answers for two different systems now right?
This is confusing me as I know little about refrigeration.

[mayball]

Therapy,
There are two systems being discussed, but they are very similar engine drive systems. However, they do have two different problems: Tom's system has an appearant insufficient condenser cooling, whereas my system has high superheat (incomplete cooling of the coldplate).
Richard,
I do have both of your books. When I was attempting to adjust the superheat, the suction pressure had already drawn down to 5" of Hg vacuum and the plate was partially frozen. The pressure did not drop quickly as it did when the moisture was freezing in the TXV. As I mentioned, I could not read the information on the top of the TXV and don't know if the inlet screen is blocked or the gas has leaked out of the bulb, but the bulb, cap line, and valve appear to be in good condition. The suction line is frosting back through the accumulator, but the compressor end of the hose is not frosted. I will check the superheat when and if the plate is completely frozen today.
Don

[Richard Kollmann]

Don, When you consider we violate many of the rules when building and installing engines driven refrigeration system so it is easy to understand why superheat and pressure readings vary from the text book examples. Frost line back towards compressor is the final control in balancing this type system. You must remember your system is one of a kind the compressor’s capacity and its speed is probably too much for the size of evaporator holding plates installed. There may be too many bends in refrigerant tubing or tubing size is causing restrictions. Having that much frost on suction line after plate is cold and seeing a vacuum in suction pressure instead of a positive pressure would indicate a refrigerant flow restriction or a pressure reading error. Adjusting Superheat or Replacing TXV will not correct this problem if there is a restriction. Closing TXV will lower suction pressure even more. Opening valve will send frost/liquid into compressor.

Refrigerant evaporation is the point where heat is absorbed and needs to be inside evaporator not in return line.. Very low suction pressure limits oil return and is not good. The problem you have is not uncommon so you may have to live with it. Some holding plates use tubing that is too small or has a restriction inside and are not good for engine drive compressor applications. Slowing compressor’s speed down may improve low suction pressure and extend compressor life.

[chala]

Richard
It has been a pleasure to follow your Master class. I would like to pass on my experience. On my boat I have a converted chest freezer, it used to be a vertical that I bought new for $400. I made a copper condenser which is cooled by fans. What I learnt making this conversion is that gravity and fluid mechanic laws apply. Air locks (gas lock) in the liquid line are as detrimental as they are in any hydraulic system. Careful charging can overcome that problem and in the building of a system good pipe work practice applies. Of course there is more to it than the description above. The freezer has been working without problem for the past 4 years.

Design spec: 2hrs work in 24. Achieved 2 ½.
Capillary, 240V AC, minimum temp achieved minus 37C, run at minus 34C with +37C ambient 80% humidity, run from generator or 24V 1100VA inverter. The famous 12/24V system.

[mayball]

Richard,
The engine was idling when the suction pressure was a vacuum, and I am not worried about slugging the compressor with 30 degrees of superheat at the bulb, but changing the pulley size seems like a good idea to solve all of the problems.
Thanks for your thoughts on this matter.
Don