Q: Where is the orifice tube on a 99 Isuzu rodeo

Your vehicle uses a thermostatic expansion valve, rather than an orifice tube, to meter refrigerant into the evaporator. This expansion valve is in the plastic case that contains the evaporator coil under the dash. You have to remove the evaporator from under the dash to access the valve. The valve rarely fails and will only clog if there is a catastrophic mechanical failure of the a/c system. If your a/c system is not working, it is best to get a complete and accurate diagnostic prior to planning a repair so that you do not spend money on parts and services that are not need. If cooling efficiency seems low, or the system is not operational at all, simply request an air conditioning system inspection and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.