97 Deville- A/C problem

First of all, thanks to the moderators and administrators for hosting this forum. 
I am trying to help my dad fix his caddy problem.  Initially he lost the a/c.  The computer says, ''freon very low'' and ''compressor will not run''.  It does the normal stuff as far as switching from ''auto'' to ''econ'' by itself.  This apparently is because it thinks it is low on freon.  He said that when trying to add freon it would go into the red/overcharge quickly.  Then he called for help. 
I jumpered across 3-5 on the relay to start the compressor and proceeded to charge the system.  The faults would not clear.  I added a little more freon to the point of being slightly overcharged, the faults still would not clear.  The system is now at the proper level.  When the compressor is forced to run, the a/c works well.  Unfortunately, the compressor will not run while the faults are in.  I found three sensors in the a/c system.  One on either side of the expansion valve and another on the low pressure side.  I think that the pressure switch is bad therefore not sensing the freon.  Is there a way I can check it or do you have any other ideas?
 
Thank you

Bump:

the process is lenthly give me your fax # i''ll fax you the troubleshooting chart.

to clear the fault codes just disconnect the negtive cable at the battery for a few min and then hook it back up. If it still wont engage then you will need the diagnostic/troubleshooting chart(s).