a/c condensor freeze up problem

During a long drive in warm weather (2 hours) with the a/c going the amount of airflow from the vents slowing starts to decrease. The fan is still running at the same speed. Doing some experimentation I discovered that after shutting off the a/c for about 20 minutes or so that when I turned it back on the airflow out of the vents were back to normal.Also, if parking the vehicle right away I also notice a larger than normal pudle of water under the a/c drain. The only thing I can think of that makes any sense is that the fins on the condensor freeze up after a period of time thereby blocking off the airflow through the system. The compressor is cycling normal and the freon is up to charge. Any ideas on how to fix this problem?

Iwould start with adding 1/2 pound to a pound of freon. that condition is usually caused by low freon.

thanks for trying to help out.
system is up to charge and the compressor does cycle in and out normally

also, it's been the shop several times and of course it checks out OK. Trouble is on very long drives is where it acts up

First off, its R-134a refridgerant, you need to be a licensed dealership to even TOUCH R-12 freon. More than likely its the fact that your vehicle is old, so your parts break down and don't function as well. Keep adding refridgerant, and get a diagnosis done, you may need a new evaporator or condensor.

-Rob

This problem is not caused by low freon unless the low pressure cut out switch is bad. It is caused by
1. The a/c pump not cycling ,turning on and off, that means 1 or both of the pressure switches are sticking after a long hot run. Have the system checked while its doing the problem. I know that will be hard to do because as soon as you turn off the system the ice melts and the pressure switches might reset them selfs.