I was servicing a Dunham-Bush 10 ton chiller at a downtown bank building, last Friday... Went on the roof to check the condenser. The HVAC sytem has been there for 50 years, I would guess. The condenser had been painted, coated, several times over the years. This tag was ready to fall off, so I helped it. Cleaned off all the paint and crud... Here it is.....

First of all, isn't it cool!!! Beautiful pressed aluminum that has lasted for 50 years! How many 10 year old units do you service, the mod & s/n are gone.

There must be internal aluminum fins to help heat transfer, and methyl chloride would have reacted with them.

Anyone know about "internal fins"?