Two comments regarding the ac. The system will definately work better with R12 that 134a, but even at its best its not as powerful as most modern systems. That said, I found that when I removed the lower dash panel to replace a faulty fan reostat that the foam material used to seal the cold air plenum had completely disintigrated with age, thus allowing cold air to leak out under the dash in various places rather than all coming out of the cold air vents. The foam that Mercedes used in that era for certain padding and other purposes was not chemically stable; every bit of it has now virtually disolved! (Check out your "B" pillars; the covering is now limp and loose because the underlying foam padding has disintigrated)

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Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
1973 Citroen DS23 EI five speed
Past vehicles;
1959 Thunderbird convertible/430
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang