I have been asked to replace the compressor.
So, refuse to do so without the proper documents or at least do so with the understanding that no warranty is provided with the repair..
The solenoid is the hot gas defrost for this unit. If this is the case, it is controlled by the defrost timer or any thermisters which may be in there. If you are jumping into a unit which has a questionable history...get out now...
Without the documents for this unit you are fumbling in the dark. Obviously something has been extensively repaired on this unit already for the solenoid to not be connected and a bad compressor to boot.