Climate Vacuum Valves (Codes)

[BillGrissom]

Recently in-there on my 1984 300D. I found 2 of the 5 vacuum solenoid valves were bad. These screw to a metal plate riveted to the side of the climate box, behind the pushbutton switch. Each has 2 ports. The output connects to an internal vent when OFF and to the upper vacuum supply when ON. The valves control vacuum to the "pods" which actuate the climate doors. The manual terms them "code 1" thru "code 5". The cable to each is labeled.

You can check them electrically by measuring ohms and/or connecting a test wire at the two pushbutton connectors (C1 - longer to R side, C2 - shorter to left side), as I did. A 14 awg wire fits in the connector holes.

You can get +12 V at C2_12 terminal (numbers on connector) with key in "run" and gnd at C1_3. Some valves actuate by applying 12 V and others by grounding. Per the manual:

Code, Term, Apply, Controls
1 , C1_10, +12V, Defrost Doors (2) - closed when ON, but Code 3 opens
2 , C2_11, +12V, Footwell Doors (2) - open when ON
3 , C2_7, gnd, Center Door - open when ON (only w/ AC)
4 , C1_7. gnd, Recirc/Fresh Door - no recirc when ON
5 , C1_12, +12V,Outside Air Door - open when ON
(sorry, can't format a table)
If good, you will hear the solenoid click when you apply above connection. You could go further and test if vacuum is transmitted, but requires wiggling off a vac hose without much room for fingers. I found code 1 and code 4 valves failed. The mounting screw was very tight in all, so soak in penetrant for hours to avoid stripping the Phillips head. I had to unbolt all valves to get those 2 out. One ear slides under the plate to secure (no screw that side).

Re replacements, I had a bag of 3 spares, but one tested bad (just made it). Also left a note that one of my 1985 300D valves is bad (code 4, so stuck in recirc). A search on P-P, rock, and ebay found no replacements, but have an entire climate box from a 1983 300D w/ 5 valves (didn't test). Re valve PN's, thru 1983 a smaller square valve was used. M-B and Febi (?) stamps, but no PN. In 1984 a valve w/ larger round solenoid replaced it w/ M-B logo, "Eaton", and "8421". They interchange (photos). A google found nothing. Let us know if you find something. I also have a set of 3 vac valves on a plate (1980's Dodge I recall), which are about the same size and could bolt on that plate if desperate (and change connectors). Otherwise a Toyota evap valve w/ 1 ear might work. I'm saving my old valves to possibly open up and rewind the coil if desperate someday. From photos, it appears M-B kept using the same "code valves" thru the 1990's. Doesn't appear the fatter round solenoid ones survive any better.

If your climate system acts quirky (most), these 5 code valves could be part of the problem and are easy to test while you have the pushbutton switch out. Good luck, especially in finding a replacement valve that fits.

[ykobayashi]

I forgot which ones, but I had two or three go out. I found them at pick and pull. They weren’t NLA when I fixed up my 300D in 2019 but they were expensive.

What I noticed is they had burns on the coils. Not really burns but brown stains and discoloration. I noticed they were the ones that came on when I was in EC mode. I verified this by measuring the voltage on the wires.

My guess was the ones that are on all the time just burn up over time. At pick and pull I used my ohmmeter to check the valves on the donor car. Sure enough the same valves were burned. So I avoided those. Sorry I cannot recall which ones. It was something like avoid evens and take odds or take the odds. Not quite your experience.

Anyhow this can be an ongoing issue with keeping our cars working.

Good you found alternatives. I think normally closed solenoid valves that run on 12v aren’t particularly rare. One of the valves I stripped off my EGR is a three way but it looks like the same type of valve and two ports can be used to substitute the hvac valve. The other should be plugged.

Eventually if we keep our cars running they’ll look like Frankenstein underneath as we substitute other parts in.

The solenoids were just solenoids…any chance they can be rewound?

ETA - just checked my handwritten notes. Apparently I changed 1&3. I specified to avoid these two at pick and pull because even if they were good they may have seen more duty. An ohmmeter check for an open coil should be used before pulling valves.