Hello everyone,

Lately, I had replaced a Maneurop LTZ88 to an NTZ215. Refrigerant is R404a. Box temperature
needs to be at least -19C.

The problem with the LTZ88, was a broken suction valve reed, which we found when doing a pump down. The causes were a bad piping design, a CFC drier being used and there was no additional components such as oil seperator and suction line accumulator. One thing to note is the condensing unit was in a false ceiling with an ambient temp of 38C. There was an orifice no.04 which was there at that time.

We replaced the compressor, done the piping designs, change drier, flush, vacuum, etc. We replaced that orifice with a new no.04 The system worked but on an evaporating temperature of -33C and condensing temp of +48C. We got the manufacturer's documents stating that an orifice no.05 was intended so we told that off to the customer that we needed to change it, sadly the customer said as long as it is working no need to go ahead. After a month we were called in saying that the compressor is overloading and cutting on the HP and the compressor was boiling hot. We suggested that we change the orifice to no.05 as per manufacturer's documents.

That was done and we had better results as we had a ducting system to have a better air in at the condenser, which was giving us +42C condensing temp, about 4K of subcooling, evaporating -25C and superheat of 8K.

After a few days the same problem occurred, cutting on the HP switch and the compressor is still boiling hot. We adjusted the pressure switch a bit higher up to 26bar normally set up at 23bars.

Only a few days ago, we had a call that the same was occurring. So we used the gauges and monitored the system. When the suction line temperature was going down to about +5C (box temp was +19 to +20C), the LP gauge started to rise up to RETARD on the gauge and the HP gauge fell down to +20C, my suction line was the same temperature as my discharge line, which led me to think that it has to be the discharge valve reed that is gone in one of the cylinders. Another thing to note that the oil was not too clear in the sight glass of the compressor.

My question could the undersized orifice and also the previous condensing temperature (+48C), have create slugging in the system? Was it normal that it took time to eventually damage the valve that badly?

Any information would be helpful.