Clicking noise probably coming from your blendoor actuator tryin to open. There is a door right in front of your heater core behind dash area that opens and allows air to pass through heater core, getting heat into vehicle. Problem is these are very difficult to get to. I'd first disconnect battery for ten minutes and maybe (keep your fingers crossed) it resets. Try and let me know what happens.
Oh man hoped that would possibly fix. I expect problem still my initial reply. Main problem is much has to be pulled out behind dash to get to part. I'd get some estimates on this repair- alot of work though for most vehicles.