When I unplug ac pressure switch the fan runs until I plug it back in.
Can I jump pressure sw to get clutch to turn on?
Can't put R134 in unless pump runs, and it is not.

Have the leak found professionally. Probably the two hoses. System would need to be vacuumed down. The freon will be recovered if serviced professionally.

Yes, if converting or adding, if the pressure is too low the compressor will not kick in. Yes, it can be jumped ( at least mine can) direct to a 12 volt sourse to get it kick in ( also this tests to be sure it will kick in and not your problem)
Once it kicks in, then you can add your coolant.

Most recharge kits include that in their instructions

I read where 2 of the 4 leads on low pressure switch should read 14 volts, but I have only 14 volts off 1 lead