94 Continental Intermittent Ac

Recently the A/C will stop blowing cold air for no apparent reason and then arbitrarily will start functioning properly. The fan speed stays constant when the cold quits. Also seems to be normal whenever engine is shut off for a short period of time. A/C is very cold when operating correctly so I don't believe there is anything wrong with compresor or any leaks. It is not vey hot out yet so I am at a loss as to what could be causing this.
Any help would be appreciated, thanks:screwy:

Still doing this today. Seems to be happening more often. I am sure that it is heat not outside air blowing in. People say their is some kind of a reversing valve controlled by the climate control setting??