So I've already called a professional and turned my heat off immediately to prevent a compressor burnout of any other problems. I just rented the home in october (in arizona) and the AC is running fine. It's been cold lately in the home so I just thought I'd test out the unit to see if it would run in heat mode, ya know to see if any maintenance was needed so my AC would run efficiently next summer(since I'm from the east coast I generally dont need heat out here). Well I turned it on, took about 2 minutes to kick on, started smelling something then the smoke detectors went off. Personally I would like to take a look at the unit since im in school right now for HVAC, but I havent learned enough yet to tackle the situation fully. I'd like the job to be done right so I made a call since the bill is covered by the homeowner anyways. Im not asking for any help on how to fix it, but what are some of the possible causes. Any insight would be appreciated and benefit my education.