Overheating and Air Conditioner Working Intermittently

I have a 2001 Subaru Outback with about 85,000 miles on it. I have two problems:

1) After returning home from shopping I notice the engine smelled hot. I checked the temperature gauge and it was registering just under the red. I didn’t notice the guague at any other time while driving, so I don’t know when it started to overheat. The coolent in the reservoir was about 3/4 inch under the full mark. Although the fan was not running when I opened the hood, it came on when I turned the A/C on and the fan fuses are okay. After the car cooled down I drove it about 3 miles, parked for about two hours, and drove home. The gauge registered directly in the middle until I was almost home and then it shot up to the red. I have not driven the car since.

2) The A/C fan continues to run, but the A/C turns off while the car is idling. It usually turns back on at some point once the car starts moving again. I live in hot and humid Florida, so the A/C gets a great deal of use. I use the A/C year round, even to heat the car to keep the windows from fogging-up.

What are the most likely problems? I want to have some idea what to expect when I take the car to a mechanic - I prefer to avoid the dealership.