A/C Clutch Cycling Switch / Pressure Switch may be the problem. Cost about $12.
How do you explain the OP's symptom that the AC works fine on the highway?
If the A/C Clutch Cycling Switch (low pressure switch) were bad, it should affect the AC in all operating modes.
IMO, the odds favor a cooling fan problem. The clue is that in the OP's report of good AC operation on the Highway. Why? Because the PCM does not run the cooling fan when the car's speed is above 45 MPH. At that speed there is enough air naturally flowing over the coil.
FWIIW, I would not recommend replacing the low pressure switch until the condition of the system's charge has been confirmed. The exception would be if testing confirmed a Hard failure of the switch itself (IE always stuck open or closed).
Advice to ANYONE out there with AC problems. The AC system can not work without air flowing over the inside and outside coils. Always begin trouble shooting with a clean the condensor coil. For
ANY AC problem, the 1st thing to confirm is the correct operation of the fans.
To the OP, are there any updates? It really helps the forum community to close out the threads with the problem resolution and "lessons learned". This give others a chance to learn from your experience.