When putting on the new high & low side connectors on a previously r12 system, should the old valves be removed before putting the converting connector on?

Thanks.

 

It all depends on the conversion fittings that you use. If you're using good steel or brass fittings, you remove the old cores. If you're using the cheap Interdynamics aluminum fittings , usually: Low side-NO, High Side-Yes.

 

Dittos what lsrx101 said.
Don't use the Cheap stuff.
Spend the extra $4 for the real thing.