A 1998 Pontiac Grand Prix GTP 3.8L uses an
orifice tube as part of its refrigerant metering device in the air conditioning system. It's not a replaceable part in the same way a filter is; it's integrated into the AC line. If there's a problem with the AC system's refrigerant flow, the orifice tube is a suspect, but often it's more likely to be a problem with the compressor, expansion valve (if applicable, some models use this instead of an orifice tube), condenser, evaporator, or a leak somewhere in the system.
Therefore, you wouldn't typically "replace" just the orifice tube. If your A/C isn't working, a qualified mechanic needs to diagnose the entire system. They will perform a pressure test to find leaks and determine if the orifice tube (or another component) is the cause of the malfunction. Often, the whole line containing the orifice tube might need replacement as a unit, rather than just the orifice itself.
