The air conditioning units im trying to clean are really dirty from coil dust . there so black after using the strongest viper coil cleaning product , the air on is still black in colour , these coils are copper . they still look black after cleaning..

Is this the best its ever going to get . or it there a product that will get them looking copperish again.

The viper product is similar to this http://www.refrigtech.com/Product/Co...ipereplus.html ,

It cleans the copper pipe really nice but can get it of the coil . need some kinda copper cleaning product ?