Actually I have experienced this problem, as I bet have a lot of other people. An AC uses a large amount of electrical current. Whenever it switches on it causes a temporary power drain and lights will often dim or flicker. My neighbor is a retired electrician from Boeing Aircraft. He said it wasn't dangerous ,and the easiest and cheapest way to eliminate the problem was to limit the use of other electrical appliances. Like running the dishwasher late at night, when the tv(s) were off. Or the washer and dryer separately. Turn off all lights that weren't needed, etc. To prevent your lights from dimming you should have your AC unit on a separate circuit run directly from the main panel. The lights are flickering or dimming because the AC unit draws a lot of current when it starts up causing the voltage to drop on that circuit. Lights are sensitive to voltage fluctuations. Contact a HVAC professional and ask about installing a "hard start kit" on your AC compressor unit to prevent it from drawing the extra power from the house on startup. Some models already have built in supression circuitry and some don't. Yours probably doesn't.
The alternator is on its way out.
Might be a weak battery
bad or failing alternator
On my Lexus I had an issue with the lights staying off when it was cold. This was the case for all of my dashboard lights. Then they would flicker back on. There are Caps on the board for the instrument panel that were blown. This was the case for my fuel cage that didn't work consistently work as well
If all of the lights flicker I would check for a loose or corroded ground. If only 1 light flickers then check to see if the bulb is properly plugged in to its socket, or if there is dirt, corrosion or rust causing a poor connection.
Most probably, a loose wiring connection.
bad wire connections inside the fan
Had that problem when still under warranty on my 02 when all lights would momentarily flicker, including the head lights, and the dealer replaced my alternator. There was a service bulletin put out on that problem. Also just recently, my lights would dim and I found a broken ground wire on the left front side on my engine block after checking all ground connections. Good luck.
On a 1999 GEO Tracker, a bad fuse can cause the headlights and dash lights to blink. A bad voltage regulator or alternator can also cause lights to blink and flicker.
check the dash board ground connection...it may be loose
Check the alternator output, you may have a failed voltage regulator or bad brushes in the alternator resulting in an oscillating voltage value. This assumes that the flicker is relalted to engine rpms.
Not enough power to starter, jump it and then ensure alternator is good. Also check battery condition.