Last September, I bought a 1991 300E from my brother-in-law (who bought it from his father). It has always been well maintained and is just under 90k.

It wasn’t until this summer that I noticed that the a/c is useless when outside temps go over 70. Fans and everything else seem to work fine, but the a/c has never been charged in its fourteen-year life. I have a couple of cans of Du Pont Freon 12 that were recently purchased by a friend who is certified to do so. I also have the proper charging hose to fit the R12 low side service port.

Considering that the system holds a little over two pounds of Freon, can I safely dispense at least one 12oz. can into the system without the use of a pressure gauge? I’m assuming that to have almost no coolness to the abundantly blowing air that the system must be short at least 12oz. or more. Am I naïve about the possibility of overcharging?

Also, it seems that the low side valve is very handy – facing up at about 3” from the right side edge the air filter. Is this correct?