Having an issue with my '98 Trooper. The heater/ac fan won't blow out any of the vents until I put a load on the engine. The fan itself is fine because it does blow once I get some revs and a load going but at idle there's nothing coming out the vents no matter the setting, i.e. recirc, defrost, top or bottom. Seems like a vacuum issue but I can't locate a vac line going through the firewall. Thanks in advance for a great forum.