Refer compressor tripping on motor overload. Please help!

[anchorman2001]

Hello, I am hoping some one on here might be able to give me some advice. I work offshore as the engineer on an anchor handling tug supply boat. Currently off of Nigeria. We have a PBUCH S.A. compressor/condensing unit for the walk in coolers and freezer. There are two identicle units side by side. Over night the unit on line had tripped off on motor overload. I reset the overload and restarted but the unit seems to be seized up and hums for a few seconds and then trips again. It had the correct oil level in the compressor and was working fine until then. I lined up the other unit and started it up and it ran well for a few days and then did the same thing. It tripped on motor overload and will not run. I swapped that compressor out with a spare that we had on board and this one runs for about twenty minutes but gets very hot, runs rough and makes a squeeky noise and eventually trips on motor overload.

Does any one have any ideas? The compressor is a Bitzer semi hermetic reciprocating compressor using 404A. The condenser is cooled with a shell and tube sea water heat exchanger. The oil level in the compressor is correct, the condenser has good sea water flow, the charge seems correct. Is there more infor needed? Thanks for your time.

Bob

[K_Neil]

Proper voltage?

[Tommy knocker]

Need a little more info. SH, volts, amps, pressures, crank case temp. A lot of possible causes. When the 2nd unit came up and was running was it cooling? Is anything else on the boat acting strange, tripping breakers or browning out maybe?

[toocoolforschool]

Clogged condensers or no water flow.

[anchorman2001]

They run on 440V 3PH, 60HZ. The voltage and frequency are good. I'm not sure what the amperage is. I'll try to check. No other equipment on board is acting strange. The suction pressure while running is .4MPa (60psi) and the discharge pressure is 1.7MPa (255psi) and it is cooling the boxes but it trips off too quick to bring them down more than a few degrees. They're all at about 30 celcius right now. We haven't had a black out or brown out in a long time.

When the second unit came on line after the original unit tripped off, it ran for several days and kept the freezer down to -20* C, cooler to 5*C. But now the new compressor won't run for more than 20 minutes or so.

Thanks for the replies.

[anchorman2001]

Water flow seems good. there is a big temperature difference in refrigerant in and out of the condenser.

[mizzterclean]

Are you checking voltage at compressor?

[anchorman2001]

I just checked at the compressor. 430V and 14.5A per leg.

[Tommy knocker]

Check SH at comp and evap. Is there a suction filter?

[toocoolforschool]

What is the temp rise of the water thru the heat exchanger?

[icemeister]

What is the Bitzer model number for these compressors? Is the internal overload tripping or do you have a starter with overload heaters which are tripping?

Bitzer has a performance calculator where you can plug in the model number, supply voltage, suction & discharge pressures and it will tell you what the amp draw should be. You can download it and do it yourself, or we can run the numbers for you:

http://www.bitzer.de/eng/products/prod/software/1

[Capz]

Check the overload relays on the motor starter. Are they sized correctly or possibly corroded? How bout the motor starter contactors? Look for corrosion there too.

[icemeister]

I'm curious as to how this system is set up. You say there are two compressors with one valved off as a standby...which I've seen before for marine applications like this...but are both the freezer and the cooler running on the same compressor, perhaps with an EPR valve on the cooler? I've seen that arrangement too.

I ask because you stated your suction pressure was running at about 60 psig, and on R404A that would typically be high enough to overload a low temp compressor.

Does this system have crankcase pressure regulator (CPR) for the compressor or possibly a pressure-limiting MOP type TXV on the freezer?

[anchorman2001]

Check SH at comp and evap. Is there a suction filter?

I haven't been able to have it running long enought to check the superheat. I will asap though.

Thank you

[anchorman2001]

Hello, sorry I haven't replied sooner. I was pumping fuel all day yesterday and didn't have a chance. I have an update on my situation. Last night I tried to run the compressor again. The noise was louder and it sounded like it was coming from the HP head. I removed the head and valves and replaced them with the head and valves and unloader from the other compressor that won't run. To my surprise, it is running smooth and quiet with no excessive heat. I didn't see any problems with any of the parts I removed but there must be something wrong. Also, the compressor that I took the head from that trips right away on motor overload, the pistons seem to be seized up in the cylinders. I can't move them at all. So that explains the overload tripping but not what caused it to seize up.

The compressor ran overnight with no issues and the boxes are down to normal operating temps. I do have some questions though. First I would like to say that I am a tug boat engineer and unfortunately I am not great with HVAC, so if the questions seem very basic, that's why.

1) The oil level was good on the bullseye when I started the compressor but now after it ran overnight, it is above the top of the glass. Is it harmful to be a little high, and if so, is there a way to drain some oil without shutting down, isolating the unit and bleeding off the pressure?

2) I'm not sure if the charge is correct. The boxes are down to temp but the pressures are low I think. Suction is 15psi and discharge is 225psi. There are some bubbles in the liquid line to the coolers. There is a lot of ice building up on the suction line in the cooler and near the compressor especially where there isn't any insulation. I am reluctant to add refrigerant because I'm afraid to overcharge. Is it harmful to have not enough charge?

3) I am embarassed to say that I don't remember how to calculate superheat. I know it is important and I am going to try to read about it on this forum asap.

There were some questions asked about how the controls for the system are set up. I don't know enough about it to give a good explanation but I will tell you what I do know: There are two identical compressor/condenser units with isolation valving. The unit off line needs to be isolated. They cool a walk in freezer to -20*C, a walk in cooler to 5*C and a provisions stores room to 15*C. Each compressor has solenoid operated unloader valves for start up and load control. The liquid line goes into the cooler and splits three ways, one line going to each evaporator and the return lines come back from the evaporators and come together again in the cooler and back to the compressor. There is valving in the cooler that controls the flow to these lines. some solenoid operated and some thermal operated. I'm sorry that I don't know exactly how it works. I took some pictures but I wasn't able to post them on here for some reason. If any one wants them I could email them.

Thanks again to everyone for their advice and support. It is really appreciated.

[A1 Burt]

superheat=temperture on suction line next to sencing bulb- then get a presure reading next to sencing bulb convert to temp from a pressure - temperature chart subtrack the two numbers then you will have your superheat --- for cooler 12 is good for low temp 6 is good - it sonds like you might be flooding back not good it will wash the oil out the crank case -all the exter oil in sight glass - after the other compressor ran for 24 hours. Good luck .

[trippintl0]

Am I the only one that is really impressed with the fact that this guy fixed the freezer, and doesn't have formal training? Granted, we still don't know what caused the failure, but at least it's up and running again! Good work! This system is over my head, sounds pretty complicated. Good luck with it. Let us know what you find.

Hello, sorry I haven't replied sooner. I was pumping fuel all day yesterday and didn't have a chance. I have an update on my situation. Last night I tried to run the compressor again. The noise was louder and it sounded like it was coming from the HP head. I removed the head and valves and replaced them with the head and valves and unloader from the other compressor that won't run. To my surprise, it is running smooth and quiet with no excessive heat. I didn't see any problems with any of the parts I removed but there must be something wrong. Also, the compressor that I took the head from that trips right away on motor overload, the pistons seem to be seized up in the cylinders. I can't move them at all. So that explains the overload tripping but not what caused it to seize up.

The compressor ran overnight with no issues and the boxes are down to normal operating temps. I do have some questions though. First I would like to say that I am a tug boat engineer and unfortunately I am not great with HVAC, so if the questions seem very basic, that's why.

1) The oil level was good on the bullseye when I started the compressor but now after it ran overnight, it is above the top of the glass. Is it harmful to be a little high, and if so, is there a way to drain some oil without shutting down, isolating the unit and bleeding off the pressure?

2) I'm not sure if the charge is correct. The boxes are down to temp but the pressures are low I think. Suction is 15psi and discharge is 225psi. There are some bubbles in the liquid line to the coolers. There is a lot of ice building up on the suction line in the cooler and near the compressor especially where there isn't any insulation. I am reluctant to add refrigerant because I'm afraid to overcharge. Is it harmful to have not enough charge?

3) I am embarassed to say that I don't remember how to calculate superheat. I know it is important and I am going to try to read about it on this forum asap.

There were some questions asked about how the controls for the system are set up. I don't know enough about it to give a good explanation but I will tell you what I do know: There are two identical compressor/condenser units with isolation valving. The unit off line needs to be isolated. They cool a walk in freezer to -20*C, a walk in cooler to 5*C and a provisions stores room to 15*C. Each compressor has solenoid operated unloader valves for start up and load control. The liquid line goes into the cooler and splits three ways, one line going to each evaporator and the return lines come back from the evaporators and come together again in the cooler and back to the compressor. There is valving in the cooler that controls the flow to these lines. some solenoid operated and some thermal operated. I'm sorry that I don't know exactly how it works. I took some pictures but I wasn't able to post them on here for some reason. If any one wants them I could email them.

Thanks again to everyone for their advice and support. It is really appreciated.

[anchorman2001]

superheat=temperture on suction line next to sencing bulb- then get a presure reading next to sencing bulb convert to temp from a pressure - temperature chart subtrack the two numbers then you will have your superheat --- for cooler 12 is good for low temp 6 is good - it sonds like you might be flooding back not good it will wash the oil out the crank case -all the exter oil in sight glass - after the other compressor ran for 24 hours. Good luck .

I took the vapor line pressure after the evaps. It read 65psi. which gives me 27*F saturation temp. and the line temp is 32*F. So subtract and I get a 5* superheat. Does that sound correct? I took the readings in the cooler near the evap.

I also took readings near the compressor on the vapor return line. 20psi suction pressure which gives a -14*F saturation temp and the line temp was 8.6*F. So a 22.6*F temp difference.

Does that make sense at all? I don't know why it is so different in the cooler and near the compressor.

[anchorman2001]

Am I the only one that is really impressed with the fact that this guy fixed the freezer, and doesn't have formal training? Granted, we still don't know what caused the failure, but at least it's up and running again! Good work! This system is over my head, sounds pretty complicated. Good luck with it. Let us know what you find.

Thanks a lot for the encouragement. I do feel like I got lucky with it but I'm very relieved to have it running. I just hope it will stay running.

[Tommy knocker]

I took the vapor line pressure after the evaps. It read 65psi. which gives me 27*F saturation temp. and the line temp is 32*F. So subtract and I get a 5* superheat. Does that sound correct? I took the readings in the cooler near the evap.

I also took readings near the compressor on the vapor return line. 20psi suction pressure which gives a -14*F saturation temp and the line temp was 8.6*F. So a 22.6*F temp difference.

Does that make sense at all? I don't know why it is so different in the cooler and near the compressor.

Yep you're checking it rite. 22* at comp sounds good. 5* at Evap is good for a freezer alittle low for a cooler and dry room but with 22 at comp its acceptable, IMO.