I have a Carrier Furnace/AC unit. I recently had the board replaced because the furnace wouldn't come on. The technician said that it needed "indoor coil cleaning". He wanted $350 to do it, but said we could do it ourselves but it would be a lot of work. He said to buy a special brush, use simple green, and be very careful to not bend the fins. I don't know for certain what I need to take apart to get to the indoor coils. Picture attached for reference. Any help would be greatly appreciated.