I have a 4cyl 02 Outback and when the AC is on speed 1 or the heat is on any speed, the radiator fans will run for almost exactly 20 seconds and then turn off for 10 seconds and then repeat that cycle. It does it worse when the recycled air mode is turned on - sometimes with that mode off the fans will run for 40 seconds before going off for 10 seconds. When the fans cycle on and off, the idle noticeably drops, lights will flicker, blower speed will fluctuate, and the car will vibrate for a couple seconds before equalizing. Blower speed fluctuation and flickering lights are only strongly noticeable when I am using the heat.

Is this normal, and if not, what could cause it? Consequences of not fixing this if it is a problem? Idle is always steady when the AC/heat are off and the car never overheats. I took the car in recently for maintenance and the shop said the AC had this problem because it was low on freon (even though it always blew super cold). They topped it off and said that ought to fix it, but if anything it is worse now.