View Full Version : sweating compressor heads

01-11-2007, 03:30 AM
Dear fellows:

During the summer, the temperature inside the mechanical room of this rack system was quite warm. Now that the winter is coming, this temperature has dropped dramatically. Some of the compressors experience long off cycles as well.
I have noticed sweat in some of the heads of these compressors while off line. I am afraid that the hot gas left in the cylinders and discharge line is condensing into liquid due to the low mechanical room temperature. I guess this liquid has the potential of damaging the plates, pistons and rods, whenever the compressor kicks in. What can I do to avoid this condensation?

01-11-2007, 08:04 PM
I thought that was the purpose of the crankcase heaters to heat up the oil and any liquid refrigerant in the compressor.

02-11-2007, 12:12 AM
The compressors do have crankcase heaters, but I guess they heat up the oil in the sump and maybe, to some extent, the adjacent area. But I am talking about hot discharge gas left in the high section of an iddle compressor, which slowly turns into liquid due to the cool ambient temperature, that might accumulate in the plates.

750 Valve
02-11-2007, 11:22 AM
I would think this amount would not be enough to cause any issue if at all condense. Unless the piping is configured in such a way that allows refrigerant from disch line and cond to migrate back to comp. An inverted trap on disch line at cond will stop this along with the discharge of comp exiting and then dropping below the level of the disch service valve before rising to cond, also forming a trap of sorts.

02-11-2007, 06:56 PM
Hi racknovice

Along with inverted traps most packs have a NRV (non return valve) installed in the discharge line, some on each compressor to prevent migration.Are any other compressors running when sweating occurs or are they all stopped?.

Unless your pack is controlled by pressure switches only - most pack controller software is configured so that the compressors each receive equal run times and will not be off cycle or idol for long periods.Either sequential or on run times.

With Kind regards


750 Valve
03-11-2007, 02:14 AM
Your macinery could just be reaching the dewpoint and forming condensation, how cold is cold?!? How long is that off cycle? Not many racks completely shut down unless they have a single load on them, if you stage your defrosts from the different loads to defrost at different times it will keep your rack running, and therby never form that sweat on the heads.