Gas and Oil Home Heating Furnaces - A/C Coils

I recently had a health check on my A/C (central type) and it was noted that there was a 12 degree split between the pick-up and the vents. The coolant pressures were fine and I was told that my coils have a baked on dirt crust that is preventing the efficient exchange of heat and that an acid wash would remove the dirt. Not wanting to pay $100.00+ for this washing, I have tried to find information online and can't seem to find any. Is this a legitimate servicing of the coils? If so how is it done?

Thanks

First if you have dirty coils, dirt and lint has gotten past the filter. Once you get the coils cleaned make sure to keep up on filter maintenance.
But to answer your question yes this is a vaild service. You could try water for free, but for stubborn dirt a cleaner can be used. there are non acid products that can be used to. Check out this site.
http://www.bbjenviro.com/products_microcoil_pds.asp

www.granger.com has a non acid Evaporator Coil cleaner 1 gal for $13.71 part number 5W402

Hope this helps