My 2003 Mustang convertible (6cyl) has recently started making a loud clicking noise under the hood that seems to come on after driving in stop-and-go traffic or when turning on the a/c. I don’t notice it when driving on the highway at a relatively steady speed. The clicking will continue for a minute or so and then stop for a while. I had also noticed a strange melting plastic or chemical smell coming from under the hood whenever clicking has happened. I had also noticed a couple weeks ago that at stop lights, the a/c was blowing warm air even when on the coldest setting. The air would then become cold again after driving for about a minute.
What could this problem (or problems) be and can I fix it (or them) myself?