i'm wondering about the location of the high pressure and low pressure air conditioning valves on my 1985 300d turbo diesel sedan. any idea where and which is which? thanks scarry

 

located far down towards the front of the engine, driver side/left side. towards the ac compressor. hidden down far, just follow ac pipes to find them.

 

Any AC system has 2 sides as you know. Separating the sides is the expansion valve, which is beneath the dashboard. The low side hoses are usually larger. The high side on the way to the expansion valve will be smaller. And the biggest hint will be the line goes from the compressor to the condensor. On that line either before or after the receiver/dryer, will be the high side service port. On my car, it's on the left side of the engine (passenger side) down near the oil pan. I have to lay on the ground to see it. If you're converting to 134a, I would shoot for just under 200psi on the high side and 35 to 40 on the low side. If the system doesn't perform as you expect, add a little more, but I wouldn't head streight for 300-350 on the high side. I know if you do the math and calculate the difference in space due to the difference in density, you'll get a much higher number, but it just doesn't work that way. I'm speaking from experience.