Sanden Compressor Puzzle

[dkall]

I have a DC generator driven Sanden Compressor driving Seafrost cold plates with Seafrosts epoxy sealed expansion valves.

I was overcharged some for about 2 months and decided to remove some chage. The generator is a small Kubota form Aquamarine, Inc and they provided the Sanden SD5 compressor. The generator purrs along at 3k rpms and the refrigeration was working fine but taking to long to pull down.

I removed about 5 psi of refrigerant and the system ran fine for one evening. The next am after about 30 minutes of running the refrigeration compressor I noticed the little generator bogging down. When I shut off the refrigeration system the generator went back to 3k rpms.

Thinking I may have to much r134a stil I took out approx 5 more psi of gas and hooked up the guage sets. HP was 130 after a few minutes and LP was 10 psi. Plates were at between 25 and 35 degrees F. I noticed the same thing after about 20-30 minutes the engine began to bog down. I then lowered the rpms to approx 2500 on the generator and the rest of the run time I had no noticable effect on the generator.

Since then I've now started up the system at about 3k rpm and after 5 minutes slowed the generator down to 2.5k. rpms. Everything works fine.

When the compressor was bogging down the generator I took some infrared temp readings the the compressor was readin 160 to 180 degrees.

I'm wondering if maybe pulling out the refrigerant left to much oil out of the compressor. I pulled it out real, real slow and felt no oil on any part near the exhaust. For those enviornmentalist, I'm sorry I couldn't recover any as I'm currently in the outskirts of Panama SA.

Thanks in advance for any thoughts.

Wondering a couple of things....
Is my compressor toast?
Should I try to run it back up at 3K?
Should I add a little refrigerant with oil? Don't have any on the boat but may be able to find some here.

[Richard Kollmann]

Your engine driven system contains 5 to 8 ounces of special refrigerant oil, How much was lost when you bleed off refrigerant? A table spoon lost would not matter much. If there was mechanical friction in compressor it would not take long to lockup.
If generator is overloaded either refrigerator’s seawater cooling is poor for some reason or tampering with refrigerant has let air into refrigerant. Too much refrigerant is another reason for a system overload, There is a very small sight glass in top of receiver describe what you see in it; System start up, 20 minutes after start up and in one hour running time.

High pressure of 130 psi is normal in tropical waters until plates start to develop frost after that high pressure should be less than 120 and maybe as low as 90 psi regardless of engine rpm. Low pressure of 10 psi is good while plate temp is above 25 degree F after that it will continuously decrease until safety device thermostat inside black flow control epoxy box cycles compressor off.

Lowering generator Rpm will reduce high pressure but may reduce AC power 50/60 cycles to a point that will damage other electrical appliances. If this were a main engine driven compressor I would recommend a compressor Rpm of 800 at engine idle and no more than 1600 compressor Rpm at emergency cruise power.

[dkall]

Thanks Richard, however it is a DC generator. Aquamarine, Inc and so when I'm pushing out low 12 amps I don't believe there will be any issue there. I don't believe any was lost bleeding. I bleed so slow that it took over an hour to bleed off 5 psi. At least there was not the feeling of any oilyness around the fitting that I used to bleed it off from, nor any oily feeling around the shelf that it was sitting on.

I can figure out the actual rpm's of the compressor but I'm looking at Sanden's page on their compressors and they show 4-6k for constant run. Humph.

I'll look at the sight glass and report what I find after my next run.

When the generator bogs down it would drop about 300 rpms and stay for a second or two then jump back up. Sometimes it would drop 100 or so and then jump back up. This after 25-30 minutes.

[DeniseO30]

Dave,
TX valves will keep trying to adjust the superheat when you play with the charge. Based on the limited amount of information your providing I'd suggest you charge until the sight glass is not showing liquid. The 134 should back up into the accumulator (if there is one on the system) Do you have any information on what the charge was? The best way is to weigh it in the charge per nameplate information. DIY with gauges my be a hit and miss effort otherwise.

I'm also guessing your system is larger then most of the 12 volt types many boxes are using. I'm also guessing you need a time delay for the compressor, If it's electric driven like your suggesting. What could be causing the overload is the hi pressure still in the discharge lines when the system shuts down. (TX valves for refrigeration don't equalize) The loads from the high side will stay high with EX valves also. Maybe there are externally equalized tx valves available from seafrost. Maybe the motor on the comp needs a start capacitor. Maybe allot of things without more information

Richard is dead on too. the plate will SLOWLY come down, taking hours even. Naked evaporators respond allot faster than holding plates too. When it gets really down to below zero on the plates the low side pressure can be 0-5 psi

Hope this helps! We need more information!

[Richard Kollmann]

OK, Forget about compressor and oil and concentrate on reducing high pressure down. SeaFrost’s plastic condensers are not efficient in warm seawater unless there is high water flow through them, this is a fact.. Describe your system’s seawater cooling system?

It is true that at 4 o 6 thousand Rpm this compressor can make ½ to a ton of ice in one hour but only a fraction of its output can be used to freeze small holding plates of less than 10 gallons of eutectic solution the rest of compressors capacity goes into heat. If this excess heat is not disposed of into seawater total systems efficiency is reduced. When refrigerant temperature after condenser on its way to refrigerant flow control valve is in excess of 100 degrees it will not be injected into low pressure of evaporator as saturated liquid. Cooling of evaporator occurs as liquid absorbs heat when expanding changing to a gas vapor.

Using 134a Refrigerant
Roughly speaking Air condition would be suction pressure of 25 to 45 psi.
Refrigerator suction pressure would be 5 to 10 psi.
Freezer temperature suction pressure zero to 5 psi.

High pressure on a system like yours that has a receiver is controlled by ability of condenser to dispose of process heat and heat from unused compressor capacity.
Recommendation: reduce generator Rpm.
Open up and clean out any seawater condenser flow restrictions.
If the above will not restore system performance by bring suction and high pressure in line remove a small amount of refrigerant.

On this system's design because of its two plates and small reciever do not attempt to fill sight glass with liquid unless all plates are frozen solid.

[dkall]

More info:

The system is an engine driven Sanden SD5 compressor. It has two plates in the freezer and one in the refrigerator. The plates in the freezer are 4x 12 x 18 and 3 x 12 x 18 and in the refrigerator 3 z 12 x 18. Freezer and refrigerator have separate valves controling them. Both plates have dual circuits as there is a 1/2 hp DC driven compressor on the other side. The condenser is the seafrost tube in the plastic and it is on my list to clean it this haul out. The water flow is approx from the Johnson electric pump that I use for cooling the generator. The condenser receives the salt water first in the chain. The readings on the condensor are 120-124 entering and 90-94 exiting, using an infrared temp sensor.


Generally; (for approx 4 years) I've run the compressor at 3k rpms (generator speed). The system calls for 3 cans of 12 oz 134a. I don't know where I am now as I had a small leak (very small amt of oil discovered - guessing less then 1 cc) and had to recharge it then. Still a small leak (I can't find yet (I do have a sniffer but don't want to warm the boxes up to locate the leak yet - will when I haul this year) so I've lived with it. Had to put about 1 can in over the course of 2 years to top up. That of course led to the overcharge. I know it was overcharged because the high cut off pressure switch kicked in at 200 psi. Let some out and rean fine for approx 3 months. To long of run times so let some more out ran fine and then next time started bogging down the 6 hp Kubota.

Last set of pressures were ... plate temp appox 30 degrees F avg of refer and freezer plates

Beginning pressure: 25psi
Time LP HP
5min 10 150
10 10 145
15 11 130 Lowered the engine rpms to 2350
pressure drops consistent
40 8 135
60 6 125
85 3 128

I tried to be as accurate as I could in the readings but obviously there is some little error.

Usually the freezer plate I shut off when the top of the first plate in the freezer in the refrigerant stream reaches less then 10 degrees F and the refrigerator I shut off when the top of the plate reaches 18-22 depending on what drinks or food has been added.

Upon start up within approx 30 seconds I had foam. I didn't watch for when it stopped foaming as Richard didn't ask for that. At 20 minutes there was no foam. I'm assuming at an hour there will not be any either.

Hope this all helps and I thank those two for their intelligent response.

Sincerely,

[dkall]

Correction: Two 12 oz cans of 134a and then a bit to account for what's left in the cans and the hoses.

[DeniseO30]

"I know it was overcharged because the high cut off pressure switch kicked in at 200 psi. Let some out and rean fine for approx 3 months. To long of run times so let some more out ran fine and then next time started bogging down the 6 hp Kubota."



Overcharging is not often the cause of high pressure because the refrigerant just condenses into more liquid. UNLESS! it's so overcharged (Danger Will Robinson!) there in no place for it go and something has to give. (seals, connections, relief devices) High condensing pressure is most often caused by restriction, blocked or failed air flow, or water flow (As in your case) on the condenser side. Your condensing water temp rise seems high. Richard may have a better awareness on it as I'm just generalizing. I am however going to say; CHECK THE CONDENSER! err.. yell or try running COLD water through it if possible.

The SD5 is fixed displacement and has 5 pistons. Not much information on their site.

found this; http://www.seafrost.com/pdfs/ED/MANUAL%20ED-134.pdf

MAINTENANCE FOR UNITS IN TROPICAL WATERS
ZINCS
THIS IS THE MOST IMPORTANT PROCEDURE. A FULL FLOW SEA FROST
CONDENSER WITHOUT A ZINC OR WITHOUT THE BONDING STRAP
CONNECTED WILL LAST A VERY SHORT TIME. BE SURE TO CHECK THE WEAR
BY INSPECTION. REPLACE EVERY SIX MONTHS OR SOONER IF INSPECTION
REVEALS EXCESSIVE WEAR.
IF THE ZINC BREAKS IN THE BRASS PLUG, REMOVE THE REMAINING ZINC BY
MELTING IT WITH A PROPANE TORCH.
ALKALI SCALE
CONDENSERS WILL SCALE AFTER SEVERAL YEARS IN WARM WATER CAUSING
HIGHER HEAD PRESSURES DUE TO THE SCALE INTERFERING WITH THE HEAT
EXCHANGE. REMOVE THE ZINC AND PLUG THE HOLE IN THE CONDENSER
WITH A 3/8” NPT PIPE PLUG. WARNING: LEAVING THE ZINC IN PLACE MAKES A
BIG BATTERY UPON ADDING ACID. THIS WILL PRODUCE HEAT AND SMOKE.
DON'T FORGET TO REMOVE THE ZINC. REMOVE THE TOP HOSE ON THE
CONDENSER AND POUR *MURIATIC ACID INTO THE CONDENSER UNTIL IT
BOILS OUT THE TOP.
WARNING: BE SURE TO FOLLOW SAFETY PRECAUTIONS ON THE MURIATIC
ACID CONTAINER.
��MOST MURIATIC ACID IS BOTTLED AT 5%-7%. THIS CONCENTRATION IS
WHAT WE RECOMMEND.
BOILING (FOAMING) WILL STOP IN (4 OR 5 MINUTES. THERE IS NO DANGER OF
DAMAGE TO THE CONDENSER. RECONNECT HOSE TO THE ENGINE AND
START THE ENGINE WITH THE THROUGH HULL OPEN. AFTER A MINUTE OR
TWO OF OPERATION TO FLUSH OUT THE ACID,

[dkall]

Yes I just replaced the zinc and know I need to clean the condenser. But in 80 some degree tropical water an outflow of 90-95 degrees doesn't seem all that high to me. Maybe I'm wrong and need to try to do that here on hook. And there is good water flow through the condensor.

With a 30 degree drop in refrigerant temp I'm thinking I'm ok but I'm listening to those that have worked in the field.

I do have the Seafrost manuals yet and look there for answers too. The have charts for proper charge and for what happens with high charge, water in system and low charge. My trend fits with the correctly charged system as per Seafrosts graphs. But as with Seafrost graphs right now I'm a little low on the HP side.

Sincerely,

[DeniseO30]

Did you use a vacuum pump? Non-condensables (air) will cause high head also. I'm also wondering about the compressor's internal or external (if it has them) that control the HP and or the low.

Looking at the charts bottom of page 44 on the guide it would seem you should be running close to a vacuum on the low side when operating close to an hour. Also, it seems the high side is ok where your saying it is.

So.. maybe it's time to scrutinize the power power supply, the motor on the compressor and the generator?

[dkall]

When I first charged the system I used a Vacuum pump. To purge the air I didn't. Obviously when there is pressure in the system I have no worry about getting air into the system.

Not sure what you mean by the comprssors "internal or external".

Also remember that was with a reduced rpm. Don't know if that matters or not.

BTW Air will compress. It's the water vapor in the air that will not and will freeze up a expansion valve. But then I should get the chart after a few minutes where I get a very low pressure form an expansion valve being frozen up. I don't.

And the issue is that the system actually bogged down the generator 300-400 rpms for a few seconds.

Since I have been running at 2500 or so I've not experienced any of the bogging I mentioned.

[DeniseO30]

Only trying to help Dave, It seems you've answered your question about rpms and bogging down.

[dkall]

I've not found out why, only that running at the lower rpm's seems to work. I've not run it at full generator rpms yet but will try soon.... maybe. I'm concerned it I do I could end up making the compressor toast and then I MUST replace it now or loose our food and ....what's most important cruising... ICE! Would rather replace it in about 2 months when I'm in a marina and using shore power for my needs.

[Richard Kollmann]

Your readings after 40 minutes are fine: Lowered the engine rpms to 2350
pressure drops consistent
40 8 135
60 6 125
85 3 128

Now if you can get these 40 minute figures at 15 minutes system should have expectable performance. All system designs have design faults. SeaFrost’s Condenser capacity is undersized for tropical waters unless water is pumped through it at rate of a ¾ inch or larger hose.
I will stay with my earlier recommendations and avoid flushing condenser withy Acid treatment for now as it is risky. You at least will have good refrigeration after 40 minutes at 2350 generator Rpm.
You describe this system as a Dual system with two compressors this was a standard for many years. Is there only one expansion valve for each system or two for each compressor?
If there were moisture enough to affect refrigerant flow by ice in TXV there will not be frost on holding plate only cold condensation. Your problem is high pressure too high overloading generator motor and unbalancing condenser sub-cooling evaporator superheat. I do not consider Seafrost’s manual charts on page 44 representative of tropical seawater conditions.

[Richard Kollmann]

Akal, If you open the engine throttle and get smoke do to excess fuel energy wasted would you clean the prop or replace engine? While in-route you would reduce power until smoke stop coming out of exhaust. Under the right conditions your SD compressor could last 25 or more years mine did. High compression and poor condenser cooling, there are three ways to solve this problem Lower RPM or reduce refrigerant volume or improve condenser’s btu capacity so it is equal to heat added by compression within compressor.