Inefficient Compressors?? is there such an thing??

[grizwold50]

Dear All,

i was was working on an liquid chiller built 2001 that cools down to -50 and heats to 150.c, customer said poor cooling, tested it and little or no cooling was happening checked pressure 10psi suction (no head pressure service port). so the compressor was pulling about 2 amps. compressor was pumping and apeared there was no blockage in the filter drier and also checked static pressure that was 40psi (checked after intial test). then decided to perform an pump test on the compressor removed all refrigerant switched unit on compressor pulled an 15inch vacuum i would of expected an deeper vacuum so would anyone think that the compressor is inefficient at pumping or damaged pistons, crackshaft or valve plate. the compressor is an danfoss sc12g on r134a.

kind regards

[tony--1]

Dear All,

i was was working on an liquid chiller built 2001 that cools down to -50 and heats to 150.c, customer said poor cooling, tested it and little or no cooling was happening checked pressure 10psi suction (no head pressure service port). so the compressor was pulling about 2 amps. compressor was pumping and apeared there was no blockage in the filter drier and also checked static pressure that was 40psi (checked after intial test). then decided to perform an pump test on the compressor removed all refrigerant switched unit on compressor pulled an 15inch vacuum i would of expected an deeper vacuum so would anyone think that the compressor is inefficient at pumping or damaged pistons, crackshaft or valve plate. the compressor is an danfoss sc12g on r134a.

kind regards

need more info on wat it is your looking at ? going of wat you said i take its a ultra low freezer .
dont think r134a gas can go that low..
taking the gas out and running the comp is not a pump test .

[grizwold50]

yes sorry the liquid chiller is on r404a. yes i know it is not an proper pump test as there is no suction service valve to shut off as these compressors are only small hermetics. and these chillers work off evaporation temperature to test these chillers you set the temperature to +20 the bath is filled with water then monitor the evap temp over an hour because the heating element counter acts the refrigeration system and that gives you your refrigeration capactity in watts.

[R. skiffington]

Is the compressor running hot? what is the rated current draw compared to the actual current draw. Is it a capillary system or does it have a TXV? Has it been running with a blocked condenser? Is the refrigerant charge correct? Is it the original compressor?

[grizwold50]

hi the compressor felt hot, its an capillary line system. removed the refrigerant and weighed it it appeared to have not lost any refrigerant, this unit is inside an clean room so there is little or no dust in the condenser over the last 9 years.

[grizwold50]

sorry and yes it is the original compressor.

[R. skiffington]

What was the liquid temp when it was running a suction pressure of 10 psi? The superheat is too high indicated by the warm compressor, this could be due to a blocked capillary, you could possibly have oil logging (less likely) in the evaporator, common in Ultra low temp systems like -80 systems. It is caused by the temp of the oil becoming too cold at some point in the evap and hardening causing a restriction. Look at your suction pressure and the temp of the liquid and ask yourself is it too high or too low, if it's too low you either have a restriction or not enough refrigerant, too high then you could have leaking compressor valves or non condensables in the system but if this is the first time the systems been open then it's not likely but remember to achieve -50 on R404a it has to run in a deep vacuum so just a small leak on the low side and it will draw in moisture and air. I would fit a High side port otherwise you're just guessing. If you have high head pressure, firstly, make sure the condenser is 100% clean, blow it out and rinse it with coil cleaner, if you still have high hp then look towards a blockage (overfills the condenser with liquid and reduces cooling capacity of condenser) or non condensables. Hope this helps

[jcook1982]

Normally running at only -50 may not need a sweeping agent for the oil but I would still suggest some kind of sweeping agent. What does the manufacturer recomend in this system for a sweeping agent? It is important to keep oil moving through the system.