A little background; I have been involved with commercial refrigeration for almost 40 years. First, as a maintenance supervisor on a large produce farm, and the last four years as a partner in in a service company. This company does daily PM on 4 large produce farms in the area and monthly PM for dozens of smaller commercial companies, i e restaurants, drive thru's, etc. Most of my education has come from the school of hard knocks, with a couple of winters spent taking courses through the RSES.
Now to the question:
I am presently working on a Morris Ice Maker, Model #NIM-40-15. This unit uses a Copeland DS6-4000-TSN compressor running R-22 refrigerant. The unit uses hot gas for harvesting of the ice on a timed schedule. (Makes ice for 8 minutes, harvests for 1 minute). It has experienced some trouble with the hot gas valve not closing on occasion and last week we replaced the valve. Upon restart, the compressor is running extremely hot, 300 degrees cylinder head temperature in about 1 minute of operation with a suction pressure of 40 lbs and a discharge pressure of 170 lbs. Normal suction and discharge should be 35 lbs and 215 lbs with about 200 degrees of cylinder head temperature.
Thinking that there must be a problem with the new valve we recovered all the refrigerant and disassembled the new valve, finding no problem. We then made a call to a compressor rebuilder and they told us that the compressor must have been slugged on start-up (which it wasn't) and had broken valves. We then reluctantly pulled the heads and checked all valve plates and valves and they look like new, no discoloration, no broken or bent parts, no blown gaskets. We called them back and were told that it must be the internal relief valve that had stuck open. Ordered a new one, pulled the compressor and replace the valve.
Thursday, we reinstalled the compressor, evacuated the system for 24 hours (100 microns), and recharged with 117 lbs of virgin refrigerant. We refired the unit on Friday afternoon with exactly the same result, 300 degrees of head temperature in about a minute and lots of turmoil in the crankcase (looks like a hurricane in there).
We had our wholesaler talk to Copeland tech and they say we need a head cooling fan. My problem with that is this unit has run for 25 years without one, and the other three ice makers in this group have also run for 25 years without one. They are all the same model number using the same Copeland compressor and all operate within the same temperature range (200 to 208 degrees of head temperature @ 35 lbs suction and 215 lbs discharge pressure.
Sorry for the long post, but thought I needed to explain the whole situation.
I believe that somehow this compressor is returning discharge gas directly to the crankcase, causing the low discharge pressure, high suction pressure, and high head temperatures.