Danfoss BD50 Compressor pulling way too many amps

[OzePete]

Originally Posted by OzePete

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

Matt, I say again your system has a low side gas leak and can only be properly addressed by following the process I previously described. As a refrigeration engineer for over 50 years I and my companies have built many thousands of systems specially these micro systems and being so tiny they need to be treated very differently to larger refrigeration units.
Gas should NEVER be added to a system without locating and repairing the leak and then evacuation at the least.
Gas only needs adding if gas has been lost and the only way to lose gas is via a gas leak.
In your case you say the electrics have been replaced and the water pump is working correctly and that when eventually running the high current slowly reduces confirming that the electrics are ok and the unit is condensing somewhat. This only leaves an air contaminated system.
Air in these tiny systems will greatly increase the consumption due to the inability of air to compress and condense similar to the refrigerant.
These systems operate at approx 5 to 15 PSI on the low side (suction) and about 140 PSI on the high side (discharge) while running, but even out to about 65 PSI both sides during the off cycle or when turned off. A suction side gas leak leaks out mostly during the off cycle then when running again, it runs on a vacuum sucking in air and often moisture. The other problem with air / moisture in the system is that it contaminates the oil specially if the system is an R134a unit with polyolester oil so best to change the oil and filter.
A rough indicator of air in the system is to feel the compressor discharge pipe (smaller pipe) while running. If the system is properly condensed expect to be hot but just bearable to feel, but if it near burns your fingers then you most likely have air contamination.
Finally, adding refrigerant without repairing the gas leak, replacing the filter dryer and evacuating is only going to lead to a greater problem later.
BTW there are some good fridgies up there specially Port Morsby.

[teneicm]

Originally Posted by OzePete

These systems operate at approx 5 to 15 PSI on the low side (suction) and about 140 PSI on the high side (discharge) while running, but even out to about 65 PSI both sides during the off cycle or when turned off.

Pete- When you say 5 to 15 PSI on the low side, you mean a negative 5-15 PSI (so a vacuum of 5-15 PSI)?

When the unit was running I could touch the discharge pipe - hot but not causing a burn.

Problem is that I've got a freezer full of meat sitting in storage in a local reefer and would like to solve the issue locally so I don't have to have a mega-BBQ as I sail off......

[OzePete]

Originally Posted by teneicm

Pete- When you say 5 to 15 PSI on the low side, you mean a negative 5-15 PSI (so a vacuum of 5-15 PSI)?

When the unit was running I could touch the discharge pipe - hot but not causing a burn.

Problem is that I've got a freezer full of meat sitting in storage in a local reefer and would like to solve the issue locally so I don't have to have a mega-BBQ as I sail off......

Matt, no it is positive +2 to +15 PSI suction, 0 to +2 PSI if a freezer and down to temperature. Systems should never run below 0 PSI (on a vacuum)
OK to avoid the BBQ!! (Unless you're sending out invites!) Do you have anyone there with gauges and some R134a that you can borrow?
If you can find gauges and some gas flick me an email so we can talk you through a temporary fix. ozefridge@ozemail.com.au

Pete

[Pyxis156]

Originally Posted by teneicm

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

I was fortunate (I think) that my installer added an access port on the high pressure line as well so I could see what was going on. My Isotherm (Danfoss compressor) only has the single port built into it like yours does.

Originally Posted by teneicm

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.

Again same as mine, and yes you will see frost on that line when overcharged.

Originally Posted by teneicm

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?

If there was a lot of frost (e.g., 12-18" or more of the coolant line frosted), I would do about a second a "squirt". When it was within a few inches of the condenser I was very conservative and did micro-squirts to try to ensure I didn't overshoot and have to add any more coolant and risk contamination.

And I did want to state that I am not in any way contradicting what OzePete is saying, but am in violent agreement with his recommendations as they were exactly what I ultimately had to do. The fact you needed to add coolant absolutely means you have a leak (albeit a very small one given your symptoms), and you will have to get that fixed at some point to resolve this problem. That said, I also recognize you are in a remote area with (I believe) no access to parts or tools like a vacuum pump or inert gas for purging, so my suggestions are aimed at trying to give you a temporary fix that will get you a working freezer until you can get back to "civilization" where you can gain access to either the tools to do it correctly yourself or to an expert like OzePete. I fully acknowledge that this is a bandaid, but hopefully one that will hold until you reach Australia...

[teneicm]

Originally Posted by OzePete

Matt, no it is positive +2 to +15 PSI suction, 0 to +2 PSI if a freezer and down to temperature. Systems should never run below 0 PSI (on a vacuum)

OK, so that was confusing me at first as I was wondering how, if the system was always operating at a positive pressure, air could migrate into the system. But I guess since that atmospheric pressure is around 14 PSI, anything below that could allow air into the system (if there is a leak).

I'll see if I can get my hands on some gauges. I have a can of spare coolant on board.

[Richard Kollmann]

Matt, It you are convinced the Isotherm additional items, ASU, water pump controller, compressor speed are not involved in this extremely high amperage then condition or volume of refrigerant is strongly suggested.

As for as I know Isotherm has not used an expansion valve to control refrigerant flow on BD compressor systems. On their units refrigerant flow is controlled by a precise length capillary tube. Pressures quoted earlier are wrong for your system with 134a refrigerant you will not see low pressure above 10 psi or low pressure much below 3 psi. High pressures above 120 is also incorrect.

When gauges are not available your unit can be serviced by use of an good ammeter that can read amperages from 3 to 10 amps. The BD50 capillary tube system with holding plate evaporator correctly serviced will draw 4 to 7 amps depending on compressor speed and box temperature.

Based on amperages you reported 24 to 25 amps and ruling out Isotherm added components non condensable contamination like air in refrigerant is one possibility.
If problem was just too much refrigerant the control module would sense amperage above 14 amps and stop compressor boot up sequence.

For information on Refrigerant charge and deep vacuum dehydration of 134a refrigeration see my web page REFRIG CHARGE
Kollmann Marine

[OzePete]

Originally Posted by Richard Kollmann

Matt, It you are convinced the Isotherm additional items, ASU, water pump controller, compressor speed are not involved in this extremely high amperage then condition or volume of refrigerant is strongly suggested.

As for as I know Isotherm has not used an expansion valve to control refrigerant flow on BD compressor systems. On their units refrigerant flow is controlled by a precise length capillary tube. Pressures quoted earlier are wrong for your system with 134a refrigerant you will not see low pressure above 10 psi or low pressure much below 3 psi. High pressures above 120 is also incorrect.

When gauges are not available your unit can be serviced by use of an good ammeter that can read amperages from 3 to 10 amps. The BD50 capillary tube system with holding plate evaporator correctly serviced will draw 4 to 7 amps depending on compressor speed and box temperature.

Based on amperages you reported 24 to 25 amps and ruling out Isotherm added components non condensable contamination like air in refrigerant is one possibility.
If problem was just too much refrigerant the control module would sense amperage above 14 amps and stop compressor boot up sequence.

For information on Refrigerant charge and deep vacuum dehydration of 134a refrigeration see my web page REFRIG CHARGE
Kollmann Marine

Richard, obviously you were referring to my post in your comments regarding operating pressures of a capillary system on R134a! I have no idea why you state that the pressures I suggested are wrong or where you get your data from, but I can assure you that what I quoted is correct. If you disagree then perhaps, for example, you can explain how a system, operating in the tropics as Matts is, can possibly have a high side pressure LOWER than that which relates to R134a's pressure operating in say a 35 degree C ambient ? Your answer should be approx 140 PSI as I had stated! Likewise your comments regards the low side pressure parameters are also incorrect.
Also if you wish to contradict another industry person's statements it would be more appropriate and professional to do so by email.
Cheers OzePete

[Typhoon]

Originally Posted by teneicm

OK, so that was confusing me at first as I was wondering how, if the system was always operating at a positive pressure, air could migrate into the system. But I guess since that atmospheric pressure is around 14 PSI, anything below that could allow air into the system (if there is a leak).

I'll see if I can get my hands on some gauges. I have a can of spare coolant on board.

In the industry we use the term PSIG the "G" as gauge , means pressure in relation to the ambient pressure.



Regards John.

[Typhoon]

I will be putting 3 of these machines (Isotherm 4901)
on Ebay shortly , if you need any parts you may want to pick up one of them.

Client went to air cooling .

Regards John.

[teneicm]

Originally Posted by ColdEh Marine

In the industry we use the term PSIG the "G" as gauge , means pressure in relation to the ambient pressure.

So if that's the case, I'm assuming Pete's numbers of +2 to +15 are PSIG? And if so, how does air get into the system if there is still coolant inside to provide a positive pressure outward? Wouldn't air only enter if the pressure of the system gets to 0 PSIG?

Sorry if I seem dense, just trying to understand how the theory relates to the practical advice on how to remedy!

[OzePete]

Originally Posted by teneicm

So if that's the case, I'm assuming Pete's numbers of +2 to +15 are PSIG? And if so, how does air get into the system if there is still coolant inside to provide a positive pressure outward? Wouldn't air only enter if the pressure of the system gets to 0 PSIG?

Sorry if I seem dense, just trying to understand how the theory relates to the practical advice on how to remedy!

Good question. Operating normally with the correct charge of refrigerant, systems have a positive suction pressure say 2 to 15 PSI (above zero PSI) and a discharge pressure of say 140 when the compressor is running. When the compressor is not running these pressures balance out to both being the same at say +50 to 70 PSI. So if there is a suction side leak the gas will leak out mostly during off the periods while pressure is higher. Now with gas lost the system operates at pressures lower than normal with the suction going below zero to being a vacuum. This is when the introduction of air and other things can occur.
The low side refers to the half of the system that is from the capillary entry to the evaporator, through the evaporator (cold plate), the suction pipe run (colder one) and the compressor itself. If the low side leak is on the evaporator (common with aluminium evaporators) often water is also sucked into the system.
Gas leaks on the high side are less damaging as that area (condenser, filter dryer, capillary etc) usually maintains a positive pressure unless a severe leak.

[Richard Kollmann]

Pete, I still can not understand the refrigerant pressures you are recommending especially in tropical climates. I though maybe it was the difference in PSIG verses PSIA gauge sets. Are you aware that most water cooled Danfoss BD compressors have much shorter lives because if lack of cooling. The only compressor cooling on Matt’s compressor is provided by adequate flow of cool refrigerant returning from evaporator. For thirty five years fan air cooled systems have operated with high side pressures of 105 psi to 120 psi . The higher pressures you recommend increases the process heat to disposed of in compressor. As for as low side pressure running as high as 15 psi the results in box temperature would be no colder than a drink cooler. Capillary tube flow control devices are dependent on gas vapor volume and not liquid volume like an expansion valve. Fifteen Psi on low side is fine on low side in a system with a thermo expansion valve because it controls a much wider evaporator super heat than a fixed volume refrigerant Cap Tube System. Matt’s water cooled freezer unit with 134a refrigerant should also not be run below 4 psi to maintain some compressor cooling and while in tropical condition both compressor and control module need additional fan cooling.

[PwrStkr]

One thing to remember is most modern refrigerants are a blend, these must be charged as a liquid. If you have a s!ow leak you are losing one type of gas from the blend. The best thing to do is remove the refrigerant, fix leak and weigh the charge back in. I have not seen a system (pre measured quick connect) that did not lable the factory charge. Yes the charge will work if one type of gas is lost to slow leak but not effectively. After repairs you should always vacuum and hold a vacuum for at least 10 - 15 minutes to verify the repairs fixed all of you leaks.
As compressors age they do get weak, if tbe system is properly charged, and the compressor is not pulling Lock Rotor Amps (LRA) then you may need a Kick Start or Hard Start capacitor. I have installed hundreds of them and seen them prolong a compressor life by years. BTW, if pulling LRA or above, the compressor is toast, and needs to be replaced.
Hope this helps in some small way.

[OzePete]

Originally Posted by PwrStkr

One thing to remember is most modern refrigerants are a blend, these must be charged as a liquid. If you have a s!ow leak you are losing one type of gas from the blend. The best thing to do is remove the refrigerant, fix leak and weigh the charge back in. I have not seen a system (pre measured quick connect) that did not lable the factory charge. Yes the charge will work if one type of gas is lost to slow leak but not effectively. After repairs you should always vacuum and hold a vacuum for at least 10 - 15 minutes to verify the repairs fixed all of you leaks.
As compressors age they do get weak, if tbe system is properly charged, and the compressor is not pulling Lock Rotor Amps (LRA) then you may need a Kick Start or Hard Start capacitor. I have installed hundreds of them and seen them prolong a compressor life by years. BTW, if pulling LRA or above, the compressor is toast, and needs to be replaced.
Hope this helps in some small way.

Yes many refrigerants are blends and any leak should be identified, repaired, have the filter dryer replaced then be evacuated before recharging. Your comments regards compressors relates to alternating current single phase types. The systems mostly used on boats are 12 or 24 VDC powered. This DC power is alternated and split into three phases electronically. They are effectively a tiny three phase motor therefore kick start relays and capacitors either start or run are not and can not be used.
Cheers

[Typhoon]

Also , you do not want to check for leaks using a vacuum . Using high pressure nitrogen is the preferred way . You can get the system up to 200psi or more and then hold the pressure there . Much better way . Moisture boiling off will give you a false reading and if you do have a leak all you are doing is sucking in air and just making more work for yourself. Also how are you going to find a sucking leak ...... use soapy water ?

Regards John