The A/C on my 300D blows fairly cold...about 50 degrees or so on the highway, which is not as cold as I'd like it in the Hell that is a DC summer, but at least it blows.

One thing I've noticed is that when I take a big, quick turn, the A/C seems to cool down for a second or two, and then goes back to it's normal temperature.

What could be causing that?

P.S. I'm getting ready to do a full overhaul, with replacing the expansion valve, flushing, etc, but I don't know where the Evaporator is located.

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)

The evaporator is located behind the dash (center) in the cabin. Dash removal required to get to it but you don't need to as it can be flushed as part of a system flush by modifying the expansion valve you plan to replace.

Before you do any of that, try the simple fixes first. I've found my AC problems over the last 25+ years are usually tied to a bad monovalve. That's a quick, inexpensive fix. Open the valve and check for torn diaphram that is letting hot water into the heater core and defeating some of your AC cooling. Do a search - you'll find a lot to read and lot of posts with pictures.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

I am about ready to install a ball valve in a heater hose. My heater core floods every time I make a short stop and I get hot air for 3-4 minutes every time I get back underway. The monovalve check valve is supposed to prevent that, but mine sometimes doesn't. Visually, the check valve appears to be okay.

I've considered the same modification. But in winter, you'd have to select full heat or no heat. How would you modulate with the ball valve?

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

You may have misunderstood the problem and/or the solution.

The purpose of the ball valve is only to prevent backflow into the heater core during the warm season. In the winter, the valve would simply be opened, returning the heater system to its normal condition. The control portion of my monovalve function is normal; it is the check valve that is finicky. The problem is that hot coolant sometimes floods the heater core when the the monovalve opens following engine shut down, resulting in a few minutes of hot air when getting back underway from a brief stop. In the winter, that's not much of a problem.

Can you share what year is your 300D? Our mind reading skills here are quite limited.

I simply replaced the entire mono valve assembly, problem solved.

My Mercedes is a 1983, as my signature says, if the query was aimed at me....otherwise, sorry for the misunderstanding.

I was messing around in there the other day and found where the monovalve is. I also did some more investigating.

With the A/C working on the middle button, and the right setting on "automatic", I was finding the response to the moving of the left wheel very sluggish....like when I would turn it all the way to hot, it would actually get colder for a minute before it decided it wanted to get hot, and vice versa.

I'm sure that my climate control is somewhat fouled up, as it's an old car, but the Monovalve also looks like it's never been opened.

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)

I believe that I've got the same issue. The vent temp of the outlet air is 15 degrees warmer than ambient..........gradually reducing to about 5 degrees over ambient...........over the next 20 miles or so, if the a/c is not used.

Any way to replace this valve...........short of replacing the entire monovalve?

I might just consider that ball valve as an inexpensive fix............

Not that I can see. The "valve" is just a plastic shuttle in the monovalve outlet port. Mine is clean and moves freely; it just doesn't do its job occasionally.

Thanks. I'm going to get a ball valve when I get the time. Many times, the ambient is about 75F. and I would just like to leave the windows open when driving locally..........but I've got to shut down the CC system to do it in the current condition.

It might be worthwhile to make sure your monovalve electrical connector is clean and tight. Another possibility is that heat soak while stopped is causing a bad connection there, so that the monovalve does not close when the engine is restarted.

Either way, shutting off the coolant flow to the heater core during the summer would solve the problem.

I do not know what would cause a difference in the cooling capacity of a car due to making a fast turn...
But thought I would mention here that a ' decreasing cooling.... which is recycled due to turning off the system for a while' can also be an indication of ice forming on the evaporator fins... which of course melts in the time the AC is turned off... allowing cooling to start again... depending on the system in question.. this can be caused by the thermosyphoning valve not working... or set wrong.... in some of our systems that is half of the ' combo Tx block valve'.....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

So...where is it best to install the ball valve? (before the monovalve)between the aux. water pump and monovalve? or (after the monovalve) between the monovalve and heater core?

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'85 300D Turbo - CA Version