What is safe time limit to keep l/s press sw. jumped to engage clutch to add r134?
If I fab a fused jumper, what amp fuse?

 

If you are just using the jumper to add refrigerant, don't worry about it. You aren't running high current or anything through the jumper wire, it is a low voltage, low current signal wire that tells the PCM that there is adequate pressure in the system for safe system operation.