Have a 73 ford f100 have good air flow out defrost and floor vents but when a/c is coming out dash vents hi is about like low on newer vehicles all the dampers seem to be working all hoses are hooked up .Does anyone have any ideas how to fix problem?

 

Sounds like a stuck damper or something like that, check the vaccum lines to them and coming off of the selector switch.

 

Does it cool well initially and then the airflow tapers off after a few minutes?
The evaporator could be icing up due to a bad AC thermostat or expansion valve.
There's really no combination of air door positions that will block airflow. I believe a vacuum leak in the line to the Recirc door or failed Recirc actuator can cause the system to allow air to flow out somewhere other than just the dash vents. This can feel like poor airflow. See if there is air blowing out on the floor or defrost ducts along with the dash vents.
The recirc door actuator only has vacuum supplied with the AC on in the MAX position. If there is an issue with another vacuum hose or actuator, you would notice it in the Heat related positions also.

 

I have a 1970 torino and a couple of years ago I had the same problem, when you turn the a/c on the air would come out of the defroster and the floor vents. I think it was a loose vaccum line to a damper under the dash. Start the car and listen for a low hiss under the dash . I know I had a problem on the same car where the clump of vaccum lines had come loose from the selector switch when I messed with the radio wires, but I don't remember if that was the time. Try moving the damper controls back and forth and maybe something will come loose. A icing evaporator coil will not redirect the airflow to different dampers. On my 1970 torino I had to remove the selector switch assy. for the vaccum controls and repair the control cluster because the plastic housing had broken that holds the plastic slide that directs the vaccum through different holes. I just put some LIGHT lube on the slide plate and made an external frame to hold the two halves together. If this is the problem do not push the two halves together with too much force you have to leave slack for the control to slide and turn. I also had to take the blower speed switch apart and clean the contacts and lube that too. This is just normal from age and the materials degrading over time. I would be willing to bet the 73 ford trucks have the same or very similar controls for the a/c. If you have to operate on the vaccum selector, do not use excessive grease on the slide plate, the vaccum direction holes a very small and will clog up. Hopefully you will not have to do all that, but it does sound like a vaccum problem. Sorry for the long post, but this just came back to me as I was writing this.