noisy unloaders?

[boilerman856]

I have a carrier 30GT chiller that is locking out on low oil pressure. The first 90(?) seconds it runs unloaded( solenoids) and raps like crazy and if the oil pressure stays up when the unloader timing stops it smooths out and sometimes will run perfect for a few minutes until the the unloaders start and then knock and locks out again. Not very experienced with the semi hermetic units and not sure where to head first. Oil pump? Unloaders?. I am home right now so i dont have the temps/pressures but do at work. Everything looks good except erratic oil pressure. Any help is gratly appreciated!

[Moparmyway]

Did you determine the eratic oil pressure from a seperate gauge, or just the operation of the unloaders ??

Have you examined the unloader gasket (usually a stamped metal one) to see if there is evidence of blowby ??

Noisy unloaders are common, but erratic oil pressure is not. Remove the unloaders from the equation, then take an oil pressure reading, it should narrow down your focus

[lynn comstock]

I have a carrier 30GT chiller that is locking out on low oil pressure. ... Everything looks good except erratic oil pressure. Any help is gratly appreciated!

Oil pressure is the operating force for unloaders. The issue is the eratic oil pressure, not the noise which is only a symptom.

Is the oil level fluctuating. See this article fora possibility.
http://hvac-talk.com/vbb/attachment....2&d=1301936059

[boilerman856]

Thanks for responding. I came back this morning and put switches on each unloaded solenoid. Isolated it to the rh bank. When that side unloads the music starts. The oil pressure is stable but a. At 20psi seems a little low. Broken valve plates or unloaded piston maybe? That head is much hotter than the rest.276f

[boilerman856]

Lynn I tried to get your attachment but a message said I did not have privileges. These are electric unloader are they operated by oil pressure also?. Sounds like an oil pump maybe. And yes the oil level fluctuates a little but still with in range.

[klrogers]

Oil pressure is the operating force for unloaders. The issue is the eratic oil pressure, not the noise which is only a symptom.

I don't believe that 06D/E Compressors use oil pressure to operate the unloaders.

Kevin

[klrogers]

Here's the document Lynn referred to.

[Dallas Duster]

I don't believe that 06D/E Compressors use oil pressure to operate the unloaders.

Kevin

I also agree, Discharge pressure.

[pringlel]

Here's the document Lynn referred to.

Thanks for sharing , very well written and educational.

[Moparmyway]

Thanks for responding. I came back this morning and put switches on each unloaded solenoid. Isolated it to the rh bank. When that side unloads the music starts. The oil pressure is stable but a. At 20psi seems a little low. Broken valve plates or unloaded piston maybe? That head is much hotter than the rest.276f

Make sure to isolate the comp properly and R&R the unloader. Your problems should go away, especially if the noise goes away when the cylinder is loaded now.

Guys,
the unloaders are solenoid operated in this case, electrically controlled.

[lynn comstock]

I also agree, Discharge pressure.

Of course this is correct. My bad.

Is the compressor being flooded? Oil sump should always be hot. Worn bearings could produce metal particles that would clog the oil pump inlet screen. Loose bearing clearances would reduce oil pressure also.

Is the noisy unloader on this same compressor?

[boilerman856]

Thank you for the ideas, I am going to replace the worst unloader and see if that changes the noise and oil pressure if so I will swap the other unloader.

If it is getting high flood back would the oil level fluctuate and and the rap worse loaded rather than unloaded?

Looks like this compressor has been changed a couple times and the HX is only showing a 3-5 temp split. Do you ever have to scrub the HX when running glycol (30%) or is the load on the AHU maybe not large enough?
Thanks again

[lynn comstock]

The oil level may or may not fluctuate. If the oil has liquid refrigerant mixed in, the oil pump will pull it in and at least some of the refrigerant will vaporize creating oil foam. This drops the oil volume pumped and the oil pressure drops. That is why I asked.

Flooding also causes bearing wear and the other problems that go with it.

There is some possibility that the rapping noise is due to the suction valves being damaged. Normally the unloader is pressing against the suction valve when unlaoded. If the suction valve is missing the unloader may be flopping around in the turbulance and creating the noise you hear.

[superfittertech]

you should pump it down. if it won't pull down quickly, more than likely bad suction valve which would explain the noisy unloader. I like to jump out the LP switch and see if it will pull at least a 20" vacuum, but others on here won't agree. If it won't pull 20" definitely, bad valves. you may need new valve plates and an unloader. The big picture is what caused this? more than likely a liquid floodback. Does this air handler have 2 stages? could be when the 2nd stage is kicking in after the 90 second delay that it is flooding back? Check your superheat.