Danfoss BD50 Compressor pulling way too many amps

[teneicm]

Hello-

We have an Isotherm 4901 refrigeration system on board (water cooled, large holding plate) that uses a Danfoss BD50 compressor.

Some background: Over the past few months I have noticed that the compressor was pulling more than a normal amount of amps at startup. When it comes on (triggered by the thermostat), it would pull 13-14 amps (at 12v) for several minutes, and then slowly, over perhaps 10-15 minutes, the amperage would slowly decline to about 8 amps (which is about normal). The system continued to run and cool, so I thought that perhaps this was a normal situation and that I had never noticed it before.

The issue: 3 days ago I shut the system down to allow the holding plate to defrost. When I went to turn it on, the system was pulling 24-25 amps at start up and the controller box was shutting it down, flashing a red/yellow "overload error" display. I swapped out both the white ASU control unit and the black controller box, but no change. Finally after several cycles of on/off, the unit hit only about 23.5 amps, and this must have been just below the threshold of the overload sensor, and the unit operated, staying at 23 amps for several minutes and then over the course of about 30 minutes, gradually decreased down to about 16 amps. After thirty minutes I shut down the system as its operation was obviously not normal. The water pump was only pulling a normal 1.5 amps, so it seems that it is just the compressor that is having the issue.

I also ran a large 10 gauge wire directly to the batteries to make sure it wasn't a voltage issue, but this didn't help anything.

Any thoughts on what's going on here?

Thanks- Matt

[Pyxis156]

Matt, have you added refrigerant to the system in the past few months? In particular, possibly shortly before seeing the high amperage draw? It sounds like my system (also a water-cooled Isotherm with BD50) would act when it was overcharged. These systems are really sensitive to the amount of refrigerant and there is a pretty narrow range for optimal functionality.

[teneicm]

Hmmmm... We did add some refrigerant about 6 months ago (unit was staying on too much, not cooling as effectively, so the diagnosis was low coolant) but the unit seemed to be operating pretty normally after that. If it was overcharged, any thoughts on why it was operable before shutting it down for a few days but now is drawing high amps?

Let's see if anyone else has some thoughts, but if not I'm game to slowly bleed off some of the charge and see if it helps.

[RaymondR]

You may have air in the system, vacuum and recharge it and see if that fixes the problem.

[Typhoon]

Sounds like you have a problem with the water pump and its control circuitry . Expensive to fix .

Regards

[DeepFrz]

If it is the water system then try flushing out the water passages with a descaling chemical. Maybe RidLyme if that is compatible with your system. Disconnect the input and output lines and run them to a bucket of solution and run the pump continuously until it cleans out the lines. Make sure the water inlet is clean as well.

[OzePete]

Originally Posted by teneicm

Hello-

We have an Isotherm 4901 refrigeration system on board (water cooled, large holding plate) that uses a Danfoss BD50 compressor.

Some background: Over the past few months I have noticed that the compressor was pulling more than a normal amount of amps at startup. When it comes on (triggered by the thermostat), it would pull 13-14 amps (at 12v) for several minutes, and then slowly, over perhaps 10-15 minutes, the amperage would slowly decline to about 8 amps (which is about normal). The system continued to run and cool, so I thought that perhaps this was a normal situation and that I had never noticed it before.

The issue: 3 days ago I shut the system down to allow the holding plate to defrost. When I went to turn it on, the system was pulling 24-25 amps at start up and the controller box was shutting it down, flashing a red/yellow "overload error" display. I swapped out both the white ASU control unit and the black controller box, but no change. Finally after several cycles of on/off, the unit hit only about 23.5 amps, and this must have been just below the threshold of the overload sensor, and the unit operated, staying at 23 amps for several minutes and then over the course of about 30 minutes, gradually decreased down to about 16 amps. After thirty minutes I shut down the system as its operation was obviously not normal. The water pump was only pulling a normal 1.5 amps, so it seems that it is just the compressor that is having the issue.

I also ran a large 10 gauge wire directly to the batteries to make sure it wasn't a voltage issue, but this didn't help anything.

Any thoughts on what's going on here?

Thanks- Matt

Hi Matt. From the symptoms described you most likely have a gas leak on the suction side of the system. The loss of refrigerant while off is now allowing the system to suck in air and other gunk when running. Air in the system causes extremely high discharge pressure and consumption as a consequence. Suggest switching the system off and have it leak tested to locate then repair the leak. Next change the compressor oil and filter dryer (use a solid core filter/ dryer), evacuate then recharge with refrigerant. Hopefully your system can be saved. Cheers, OzePete from Ozefridge

[Pyxis156]

Originally Posted by teneicm

Hmmmm... We did add some refrigerant about 6 months ago (unit was staying on too much, not cooling as effectively, so the diagnosis was low coolant) but the unit seemed to be operating pretty normally after that. If it was overcharged, any thoughts on why it was operable before shutting it down for a few days but now is drawing high amps?

Matt,

We were having a very similar problem with our system running too much and not cooling effectively. Turns out our problem was an extremely slow leak at one or more of the quick-connect fittings due to the o-ring not sealing completely (they were 8-years old). The initial "fix" was to do as you did and add some more coolant, and things seemed to work again... for a while. Eventually the system started cooling poorly again and we added more coolant. The third time having to do this, and it took 5-6 months between recharges due to the leak being tiny, I decided to try to fix the problem once and for all. I do know that the last two times I slightly overcharged the system as evidenced by frost forming on the first few inches of the coolant tubing running from the fridge. I did this intentionally knowing that it wasn't ideal, but it would buy me more time between recharges and the system didn't seem any worse for it. Note that this entire time, the fridge was kept running so it was never allowed to warm up to ambient temperature.

In preparation for fixing the problem once and for all, I shut off the fridge, then something came up and I didn't get to work on it and needed to start it back up for another couple of weeks before I could get around to working on it again. Upon starting it from an ambient temperature state, we had the same symptoms you have, drawing lots of amps and eventually an overload signal on the controller. I thought it was a controller problem, but swapping controllers did nothing, same symptoms. After checking voltages and a lot of other troubleshooting, I eventually broke down and bought a refrigeration manifold with gauges. Using the gauges and experimenting with the starting charge, I could see what the unit was doing and realized that if the system was starting "cold" (i.e., the fridge was already cold and just starting a cooling cycle), the pressures on the high and low pressure sides responded one way, but when starting "warm" (in my case ambient temp was in the upper 60's to low 70's Fahrenheit) and with the unit slightly overcharged, the pressures would start higher and the low pressure side never dropped below 10-12PSI and the pressure on the high pressure side would get really high, eventually leading to the system shutting off with the overload signal on the controller. The short-term fix was to let out a small amount of coolant allowing the system to start normally again from an ambient temperature. Once it got the fridge down to operating temp, you could actually increase the coolant charge a bit and things would keep working... until you shut it off and things warmed up to ambient where I could reproduce the overload problem consistently.

The long-term fix was more onerous. I still had my slow leak so I replaced all my o-rings in the quick connect fittings, and I then eventually determined that I had some moisture in my system causing an intermittent ice(?) blockage in the evaporator that would form when the system ran. The blockage caused the system to run continuously and the evaporator to never really cool (temps on the evaporator would be slightly above freezing). It was confounding because if I let the system warm up, the blockage would melt and sometimes the system would run for days before the problem reappeared, it was infuriatingly random. I believe that the moisture entered through the leaky o-ring when the system went from running to stopped to running and the pressure changed within the system. It was possibly exacerbated by poor coolant line purging prior to recharging the system when I was just starting to try to deal with this issue and was ignorant of the importance of doing everything possible to prevent contamination of the cooling system.

After replacing the o-rings, I then bought a micron gauge and a vacuum pump, as well as an Isotherm filter/dryer that connects to your coolant circuit using the quick connect fittings. Due to the contamination in the system it took multiple cycles of creating a vacuum and then purging with inert gas to get the system to hold a good vacuum. Ultimately it required using a heat gun to warm the condenser and the compressor to help release the moisture while the vacuum pump was running. Eventually I got the system to hold a low vacuum and remain stable even when I heated parts of it with the heat gun, indicating the system was clean and dry. I recharged the system and it has been running perfectly for eight months, and the cooling cycles to bring the system down to temp are shorter than they have ever been so the system seems to be running more efficiently as well.

So to answer your question, your system didn't cool effectively so some coolant was added to the still cool fridge, and it is possible that the system was slightly overcharged. The system continued to run so the coolant never reached ambient temps, but once you shut the system off for an extended period the coolant reached ambient temps and the pressure in the system increased to a level you would never see when the coolant is at operating temps. I was able to reproduce this phenomenon in testing, and this could explain why the system worked "normally" when at operating temp, but failed when starting from ambient temp.

With luck you are catching things early and do not have any moisture in your system (yet), just a slow leak that if you fix you may be able to recover from by simply recharging your system. I would suggest you consider replacing all your o-rings as that is the easiest place to start with a leak issue (and I have since learned that they are considered a maintenance item by Isotherm). If you don't have access to the equipment or the desire to purge your system with a vacuum pump and test to confirm the leak is fixed, then hopefully simply getting the system to correct charge will get you back up and running again. But if you do find the system running poorly or continuously, you may have enough contamination in your system to cause your system to run inefficiently or even create blockages that will require you to do a complete purge like I ultimately had to.

And I urge you to be extremely meticulous about purging your hoses and manifold (if you use one) so as to not introduce contaminants when charging or adding coolant to your system. Having to completely purge the system and removing all the contamination was a huge PITA!

Sorry this was so long and hope it helps...

[Richard Kollmann]

Problem solving is extremely difficult on Danfoss 12/24 volt compressor systems when creative design for marketing purposes was more important than those designed for continuous trouble free reliability.

Matt, your first step is to determine if high amperage is caused by:
1. Refrigerant volume or Refrigerant contamination.
Compressor running at higher than design speed.
Seawater condenser contaminating complete system.
Electrical trouble in Danfoss part of refrigerant system excluding water cooling.
2. Isotherm Variable speed water pump controller.
Isotherm ASU assembly or control head.

To isolate #1 areas from #2 items remove ASU and place a jumper wire between Danfoss control module terminals C and T. Connect 12 volt power wires direct to Danfoss module. Compressor should now run without interference from Isotherm components.
If refrigeration system is OK compressor will run at minimum speed 2,000 rpm
Amperage will be about 5 amps for about 15 minutes, if system temperature at start was at ambient temperatures. After 15 minutes seawater condenser will start to get warm do to loss of pumped water cooling. But amperage should not exceed 7 amps when condenser temperature is below 120 Degrees F.

[Cliff Meima]

When you turn off the system to defrost it, the refrigerant in the system immediately begins to warm and expand raising the pressure in the system dramatically. The compressor amperage draw will be higher (as you noticed) when starting with the system at high pressure. This is normal. I suspect that you incorrectly added refrigerant without putting the gauges on and measuring the pressures.
The first thing you should always check on a marine water-cooled unit is water flow, not refrigerant charge.

[teneicm]

Richard- I removed the Asu unit and jumpered the controller and still got the same result.

Pyxis- That does sound possible. Might try and bleed off some refrigerant, but would like to hear back from Richard on what he thinks next steps should be. One of the problems is that I don't think there are any technicians or resources here (NW Solomon Islands) that have a vacuum pump to allow me to purge the system, but I'll start asking around in earnest.

The water cooling portion of the system is working fine. We always keep a close eye on it as it is very prone to getting clogged up.

One of the problems with the Isotherm system is that they designed the system with only one access valve on the compressor (to add or remove coolant). There aren't separate ports from which to check the high side and low side pressures.

[Pyxis156]

Matt,

Shortly after I posted I saw your website link and explored a bit... my wife and I are very jealous! It also hit home that you are in a remote area so it may behoove you to be conservative in dealing with this so you don't end up with a non-functioning unit for your trip to Australia.

A little more info... when the unit sits for a bit not running, the pressure between the high and low sides equalize over time. If you do go the route of releasing some coolant, I would suggest you do it when the system is at ambient temp or when the system has sat for a while after not running. That way there is still some decent pressure in the low-pressure side of the system that the access valve connects to and you can be sure to release pressure from the system, not introduce air into the system which could conceivably happen if you wait until the system has run for a while and the low pressure side is truly at low pressure when you try to release it. I found on our system when it was fully cranked and in max-cooling mode (i.e., the surface of the evaporator is well below freezing), the pressure on the low side could be at or just under 0 PSI. If you try to release pressure then, you stand a chance of flow going the wrong way and introducing air and contaminants into your closed system.

I would also propose you be very conservative by releasing small amounts until you get the thing to fire up and keep running. The amount of coolant from undercharged to overcharged is surprisingly little on these units.
Release a little pressure, start the compressor and see if it keeps running. If it stalls with the overload signal, shut off power, let it sit for a bit to equalize out the high and low sides and then release a little more pressure... repeat until it fires up and stays running. If you can get to the right pressure and avoid having to add more coolant, you really reduce the chances of contaminating the system and creating a lot more headaches.

Good luck and please let us know what you learn and how things work out.

[teneicm]

Originally Posted by Pyxis156

Matt,

Shortly after I posted I saw your website link and explored a bit... my wife and I are very jealous!

Ha! After I read your post about how you solved your issue I was a little jealous thinking, "Oh to be in the States, with access to the right tools and skills!" Of course this thought was a bit exacerbated by the fact that the roller furler has also gone belly up, and the water pump lip seal has gone off again... so there's been a few more breakdowns than usual around here!

So how did you get the proper amount of coolant in without having access to low/high side gauges to check the pressure levels? A measured, weighed amount? Any idea how much coolant a BD50 requires if starting from zero?

[Pyxis156]

Originally Posted by teneicm

Ha! After I read your post about how you solved your issue I was a little jealous thinking, "Oh to be in the States, with access to the right tools and skills!"

The grass is always greener... but I hear you! I was very fortunate to have access to everything I needed and I learned a lot.

Originally Posted by teneicm

So how did you get the proper amount of coolant in without having access to low/high side gauges to check the pressure levels? A measured, weighed amount?

Well, the good news is that after trying all sorts of things and reading way too much refrigeration literature and trying really hard to come up with a weight or known volume or set pressures, the best answer ended up being the simplest and least technical. Essentially you want the coolant to change state and stop cooling and transport the heat out of the system and back to the compressor shortly before leaving the evaporator, and I assume this applies to a cooling plate as well. [And my apologies to any professionals reading this and rolling their eyes, but that explanation made it clear to me]. So what I did was start the system when the fridge was still somewhat warm and would need to run for a while to get to temp and then monitored the return tubing for frost forming on it as it left the evaporator. If I saw frost, I would bleed just a bit of coolant and surprisingly could see the effect almost immediately with the frost receding back towards the evaporator an inch or two depending on how much you release. Once I got to no frost on the tubing, I gave it one last very small release as the literature indicated that a slightly undercharged system performs better and is more efficient (i.e., uses less power) than a slightly overcharged one, and my tests monitoring amp draw of the compressor confirmed that. It was as simple as that! No gauges, no weighing, no measuring pressures. And best of all, that is the theoretically optimal amount of coolant for your specific system, something no predetermined weight or pressure could achieve since every system is unique.

Originally Posted by teneicm

Any idea how much coolant a BD50 requires if starting from zero?

Since the volume of the overall system (including how much tubing between the compressor and your holding plate as well as the size of your holding plate) dictates how much coolant you need, I am not sure my results will translate to your system. That said, I found slightly less than one can of coolant would fully charge my system from a complete vacuum. I also found when monitoring my gauges that filling the system at an ambient temp of about 70F to just over 20PSI would get me close and then I would tweak the amount of coolant as I explained above.

Hope this helps...

[teneicm]

Pyxis: Ye, it does help! Couple of questions: Does your Isotherm have more than one port on it? You mention hooking up gauges....

Also, my supply and return line are in one tube (the two lines encased in one outer tube). Is this the same as yours and were you able to see frost on that line? There may be separate lines at some point, but they are so far back in the corner and covered by the holding plate that I can't see them.

Finally, when you were bleeding off the excess gas, how long of a 'squirt' were you doing? Just a split second or opening the valve for a second or two? Or longer?

Thanks-