Slow oil return - Carrier 5H86 compressor

[mike3068]

Currently there some problems with the oil returing back to the compressor (oil level just below slightglass). The chilled water return temp to chiller was 11degC and the suction pressure was at 2bar. TEV superheat was set at 8degC. At times the net oil pressure goes below the 2.5bar recommended. if this were to persist, the unloaders will not be able to load due to lack of hydraulic pressure from the oil. The temperature controller (Honeywell) was set with a desired temp from 9 to 12deg with 1deg differential. Ambient temp varies from 32deg in the day and 20deg at night. AHU coils were also chemically cleaned with temp diff across coil within 2 to 5deg but the air flow rate wasn't checked yet.

One of the compressors was recently top overhauled and found the piston crowns with dented markings and the suction valve plates broken. What's the likely caused? I'm under the notion of an oil slugging or floodbacks due to sudden load increments. But here again the distance from the chiller unit (below the compressor suction head) is about 1m. Another finding is that the TEV bulb is place on the vertical pipe before the suction not at 4 or 8 o'clock on the horizontal pipe.

[Iceman Ian]

mike

Much more detail and data would be required to make any sort of informed recommendation, but it sounds like liquid refrigerant at the compressor, possibly caused by low water flow through the chiller....it could be as simple as sludge build up in the oil return float outlet orifice reducing the rate of return oil, or faulty crankcase heater, allowing liquid refrigerant to condense in the oil during shut down periods, especially during cool nights. TD across the AHU coils seems minimum, which could also indicate low chilled water flow. Broken suction valves is also an indication of possible liquid refrigerant flooding or oil slugging, among other things. Is this a factory built chiller, or made up on site. Is the chiller a small set with the one Carrier comp, or is the chiller large with multiple compressors, and if so are the other compressors having the same problem. Hope this assists in some way and I would be very interested in following the rectifications.

Good Luck.

[Ben-Hur-Cool]

Hey Mike,

It sounds like you already found your problem.
The compressor did suffer causes like slugging/floodback.

And you are also right that the TEV bulb isn't mounted right.
It has to be mounted horizontally, and then depending on the size of your suction conduit you place it accordingly.
DIAM 10 --> at 1 o'clock
DIAM 20 --> between 2 and 3 o'clock
DIAM 30 --> between 3 and 4 o'clock
everything above DIAM 30 you place at 4 o'clock.

This should help with your OIL problem as well.
Because of the refrigerant fluid that causes floodstarts.
Also check if your crankcase heater is still functioning right. Not to HOT and not to COLD.

Ben

[wombat]

Mike,

Ensure that the compressor pumps down correctly when the water reaches set point and the solenoid valve is not leaking otherwise liquid refrigerant could return to compressor. Should suction pressure rise quickly after pump down when the solenoid valve seats correctly, the valve plates probably have failed.
If the compressor is noisy, damage may already occured. I'm assuming that one compressor per refrigerant circuit.

Gary

[WINJA]

Is the tx valve bulb well insulated , this sounds like a low water flow or load problem , Have you tried controlling the leaving water temp instead of return?