What is this clicking noise?

Today, in my 2005 ford focus, i turned on the a/c- really for like the 3rd time since last summer. The engine seemed to be struggling- don't know if this happened before or after i turned on a/c. the engine sounds like it is shifting gears? while it is in park? i drove 5 blocks home and i know my car very well- something is up. it never makes any sound like it is now- like it is working harder than it should need to. normally it is so darn quiet you would think i was driving a prius. also as i drove it seemed like the temp. gauge was rising pretty quickly- but not in one smooth movement. it would start and stop and rise the same amount each time. i expected, at this rate, that it would soon overheat. but it never happened. nonetheless needle was directly in middle and rose super fast- enough for me to take notice. when i parked at home i sat and listened and it was making the same noises- almost like power was being drained from it- but not in a battery kind of way. if that makes sense. when i turned off the car i heard a click. then i heard it again. thought i was losing my mind. but click kept occurring- like clockwork- no pun intended. it was from inside the car- almost like it was from the console above parking brake. also when i got out of the car i felt the hood- just to check- perfectly cool. research suggests this may be door blend actuator, moisture in distributor cap, issues with fuses/relays, temperature blend actuator, or starter or solenoid switch. i need to know what it is- but also i need to know if the a/c being turned on and the clicking have anything to do with the engine- because they seem to be related as they occurred at same time- but research online makes the problem- whatever it is- seem like an interior or electrical issue exclusive of engine. i also am planning on changing the fuel filter- simply because i am due- and maybe it is that? maybe the engine isn't being fueled properly/ intake regulated? Anyone have any answers before i visit a mechanic who may or may not try to take advantage of a cute girl? =)