Buying 78 300D

YES. This servo / amplifier system is awful and ought to be junked.

Go to

and look at their digital retrofit kit for this application. Their kit replaces the servo and the amplifier, both of the troublesome elements of the OEM climate control system.

I installed one in my '80 300SD and am pleased with its performance.

Hopefully there are no other "modifications" to the climate control system of the car you have in mind.

Are you satisfied with the acceleration of the 300D? If not try a 300D Turbo or a 300SD which uses the same turbo motor.

Last year I had the R-12 Freon "topped up" in my 300SD's and was told that the R-12's cost, though high was not too much higher than the R134a whose price has risen a lot. Price it both ways: R-12 and conversion to R134a.

On older cars, it is better to stay R12 due to the hose and seals. The hose is the most important part as R12 hose are not dense enough that the R134A will sneak out.

Thanks for the link. I have found a reasonable :) mech. who has been working on these cars for over 25 years and have it in the shop getting checked out today.

I had mine converted to R134A about 10 years ago, with original hoses and no leakage problems to date. However, I did the conversion based on the R12 becoming increasingly high price and forecast to disappear. With the way things are now, I'd keep it R12.

Regarding the climate control system, another alternative to consider is replacing the servo with one from Performance Analysis, in TN. They rebuild them and use a lower case made of aluminum, which eliminates one of the main failure modes. Cost is $600, I think, and after the 1 yr warranty, they will fix it for life for $100. As pointed out, this assumes they haven't screwed up and modified the whole climate control system in your car.

Also, I don't think I'd be too excited about this non-turbo diesel. There are 300SD's available from that era that have much more HP, making them more drivable, plus you get a bigger, nicer car for not much more money.

I've been wondering about this setup. What happens when the heat is off? I mean, is the electric water pump also turned off, or does it push on the closed valve, or does the coolant get shunted somehow? When I rerouted my hoses to bypass the ACC, the only thing I could imagine is that the secondary water pump keeps pumping but that the servo shunts coolant flow. Is that the case?

-tom!