Stal S24 unloader and feedback

[fireandice]

Hi guys, I am seeking information on the slide on the S24. The compressor was reconditioned 2 years ago by johnson controls but has not been used because of an unloader problem. This is a standby system that is a duplicated backup so I am keen to get this system running to provide a bit of safety for the coolstore.
When the compressor is running the slide keeps going to the fully loaded position and the PLC pulses the slide down to unload but it keeps "leaking" back. I have altered the PLC to pulse the unload signal for longer and it is running ok but I would like to fix it properly. Any suggestions or exploded views would be greatly appreciated.
The other problem is the feedback from the slide, how does this work and how do I test it, is it just a variable resistance and if so what resistance should I measure.
If there is any way to buy manuals I would be keen to hear about it.
Thanks for your time.

Mark