Need help with 73 Mach1 AC

The AC system on 71-73 Mustangs works very well when all parts of the system are functioning properly, so I don’t think a stronger fan is the proper solution to your problem. The water on your passenger side in association with your AC issues points to a possible cowl rust issue and/or heater box blockage at the cowl intake (note: mice love to make nests there).

Open the hood and remove the plastic vent covers at the base of the windshield. Reach in and remove any debris blocking the left and right cowl drains. Feel around the base of the passenger side cowl chimney for rust through. With proper contortion, you may be able to feel for any obstructions inside the chimney. Ultimately, you’re best off removing the heater box so you can do a thorough cleaning of any obstructions and a thorough inspection of cowl chimney rust through. (note: labeling each vacuum line and taking a few digital pictures before disconnecting them will simplify re-assembly.) If you decide you want to disassemble the heater box (after you’ve removed it), be sure to spread the spring clips open by inserting a large flat head screw driver into the slot provided. If you pry the spring clips off by inserting a screw driver in between the fiberglass housing and the spring clip, you will damage the fiberglass housing and be unable to put the spring clips back on.

If you have cowl rust through issues, you’re looking at a substantial amount of repair time. I’ll leave it at that for now and wait to hear the results of your inspection.

Good Luck