York DXS45 capacity slide problem

Hi to all the ref engineers in this forum. I'm new here and will introduce myself before posting my question.
I'm into industrial refrigeration compressor overhauls for 15 years now and pretty much have worked on almost all brands. I live in The Netherlands and started working for STAL. Still work for this company but as you all know under several different names.
My question is a problem with a YORK DXS45 semi hermetic screw which we overhauled because of capacity slide problems. After the modification with a bypass valve and a new capacity valve the slide valve stays in 100% position even with the electrical connection off. All seals, bearings etc. were renewed but the problem still is there. Valve is tested on other compressor and works fine. Who has had this experience and maybe has a answer for the problem??
Thanx in advance for any reply

The Screwdoctor

Wires crossed? So instead of unloading it keeps loading!

Happens more then one thinks!

just beneath the name plate is a 1/8 plug. remove this and put a gauge fitting in. measure pressure from here when running and compare to suction pressure. if difference is more than 10% then your seals are knackered.

Thanks for the quick reply's, the signal to the valve is correct. I've measured from 0V to 12V when it is loading from the panel. Keeps loading even with the connector off the valve!, must be internal leakage would be my guess. The internal lipseals are real SOB's because they wear out fast. In this case the compressor has brand new lipseals so we can count that one out. The modification with an external oilreturn pipe has been performed so the slide would always be able to drain its oil, why does it still go to maximum position and only goes back to minimum when stopped???

Hope somebody had the same problem.

Thanx

The Screwdoctor

The lip seals can be easylie damaged during rotor assembly. You can check this using the procedure described by swampy. If the lip seals are ok i would suggest to replace the the slide valve piston. Did you used the original York bypass line including the ball plug? How many running hours had the compressor before overhaul?

i have got this problem with York YR Screw chiller. The chiller keeps loading up till it tripped on over current. Took out the loading valve and it still load up. Suspect could be the slide valve problem. Decided to by pass the unloading as it crosses the 70% current mark but to no avail. Still tripped on current overload. Change the capacity control but still the same.
do you think it is the slide valve problem? what should be my next step?

Pls Help!!!!

Hi screwdoctor, not meaning to teach granny to suck eggs but did you install the ball plug during the retrofit?

the ducts into the suction port may be closed

hi, by my mind you have bypass en capacity cylinder, check the piston seal and piston relif valve