Hi

i've been back today and run the compressor from a cold start, started and run fine getting a reading of about 0.5amps on the start winding when running.The system is running on R409A and was running with a discharge pressure of around 100psi (30deg C) suction pressure of around 5psi (-20deg C) cabinets should be around -20deg C they started to pull down in temperature, amps around 5 amps ran well until i stopped it to set pressure switches and then failed to restart, i left it for 30 mins restarted ok but then would not run consistantly (kept tripping on the klixon, or the start relay would energize also causing it to fail on the klixon (locked rotor reading of 25amps) left it for a further 30mins but a repeat of the above occureed, and would not run for any period of time, for the next few hours.
I measured the windings resistance before i left, the casing was warm, i had a reading of around 7ohms (common to start, 2.5-3ohms common to run and 10.5 run to start so comp seems ok.
Temp on suction line was above zero deg C as no frosting was occuring so the superheat is quite high (so i don't believe there is a threat of liquid flood back), the only thing i'm not sure of is if there is oil flooding back (i don't how i would be able to detect this. i'm wondering if the oil (as the compressor is mounted above the evaporators by approx 6mtrs) could be being pulled up the suction line and starting to hydraulic the compressor casuing a high load on the motor windings causing the relay to re-energize etc, etc.
The other possibility is due to the high suction superheat, could this be causing the the windings to overheat and the klixion trip that way, i have constantly felt the compressor head and body and would not say it has been excessively hot causing a trip or excssively cold threat of liquid.
Can't seem to keep this thing running.
Thanks monkey spanners/ Brian UK
The relay is not a current relay (i think these are for smaller compressors), it's the voltage relay (the little box with 5 or 6 terminals remotely mounted from the compressor, not mounted on the compressor terminal pins.

Thanks

CB