Liquid Tide
laundry detergent should do it. It will even take off cosmoline when used with hot
water. You can find all kinds of "eco friendly" solvents
sold in auto
parts stores that will say if they are safe for
aluminum, but Liquid Tide should be readily available and it will clean off any other crud that is in there. You may need a bag of pipe cleaners or a pressure sprayer, the kind used to spray weed killer, to really get in between the fins.
Pulling a system apart means more than recharging it. You need to apply a high vacuum first to empty it out (illegal to just open it up and dump the gas), then also be concerned about proper
seals, not just recharging it. And apply vacuum again before recharging. A
project to be avoided at all costs if the system is working.