A/C Mystery

My A/C stops cooling after driving 20-25 minutes. I can turn it off for a few minutes and it will then come back on but for only 5 minute intervals. Took it to shop had A/C reset, new cabin air filter, found low side pressure too low, verified the refrigerent level and put in the new cabin air filter. Problem still exists $200 later- mechanic’s solution is to take it to dealer. Arrrgh.

This could be evaporator freezing which can be caused by the low side pressure being too low. (too low only up to a point.)
The symptoms can be low airflow out of the vents and lack of a condensation drip underneath the car on the passenger side.

The post is sketchy but does this mean the refrigerant level was brought up to what it should be?
The cabin filter should have nothing to do with this unless the evaporator is freezing and it was wrongfully assumed that a dirty cabin filter was slowing the airflow down.

Is the evaporator draining properly? There could also be electrical issues with the control system. There are at least a couple of pressure sensors designed to protect the compressor from damage. One of these may be failing, and turning off the compressor.

Yes, it is my understanding that the refrigerant level was brought to where it needs to be. After that the shop did another test drive and the issue still arose. The cabin filter was replaced because they did think that possibly there was an airflow issue, even though they (the shop) said there was just slightly above expected dirtiness to the filter, I had them replace it, as a just in case measure.

One other thing I have noticed is an exceptional drop off in air flow level when I push in the upper level vents and then the lower level vents. When both flows are in the on position it seems the upper level (based on when it is only selected) has a flow of only about 30% of what it exhibits when the floor vent is not also selected.