95 e300d, Duovalve and AC - PeachParts Mercedes-Benz Forum

connerm · #1 04-22-2017, 11:26 AM

Working on my ac. So far...

Verivied 12v getting to klima
Verified that pushbutton unit sending signal to klima
Verified slight resistance at pin 7 to check clutch coil resistance
New blower motor.

I want to do another test and check clutch coil resistance at connector on the compressor. It has wires going into it - Yellow White White. I checked for resistance on the pin on the compressor where the yellow wire fits and got slight resistance. Nothing registered on my multimeter on either of the two pins where the white wires fit.

I reconnected Yellow White White wires to compressor then jumped 5 and 7 in the klima socket and started it up. Ac clutch still did not engage.

I suspect the coil, but I would like to verify it. Is there a simple way to check for voltage with a test light or multimeter?

I listed Duovalve in the title because all of a sudden, the coolant expansion tank is well above the normal level. Does anyone know of a connection between a failing duvolve and the ac system? The duovalve in my car is the second one. I replaced the original back in 2008 (when I didn't need two sets of eyeglasses to work on my cars)

Diseasel300 · #2 04-22-2017, 11:49 AM

The coil on the clutch should have a very low resistance, something like 1-2 ohms.

I'm not familiar with the duovalve or the system in your car, so I can't help you there, however I think it would be unrelated that the coolant expansion tank would move at all from anything involving the climate control system.

sixto · #3 04-22-2017, 12:14 PM

You have a duovalve on a US spec W124? I thought they all had single channel heating. And the model specific monovalve is prone to cracking. I've heard of the coolant line in the washer reservoir rupturing and filling the washer reservoir with coolant but not the other way around. If there's no engine oil or ATF in the coolant, maybe it's just running hotter these days.

Soxto
83 300SD
98 E320 wagon

connerm · #4 04-22-2017, 04:00 PM

There are two pumps on the water valve, so I assume it's a duovalve. The one I put on in 2008 is leaking a little bit. I'll check to see that its not coolant. That would suck. Car has been running fine lately, except for the ac not working.

Jeremy5848 · #5 04-22-2017, 06:57 PM

The '95 E300D indeed has a monovalve, Sixto, the one that leaks. The twin exits from the heater core join together at the base of the valve, which has a single electric plunger. The valve is special in that it never shuts off the flow of coolant but rather directs it either through or around the heater core. IMHO, this is purely for smog reasons—a constant flow of coolant through the head makes head temperature easier to control. It also means the valve/pump combo is unique to the '95 E300D, except for a very few, very late 300D2.5 OM602 turbodiesel engines. Thus the extreme price, now well over $500.

Jeremy

connerm · #6 04-22-2017, 08:38 PM

Thank you Jeremy. I was hoping to hear from you about this. Was it you or someone else who did an informal survey of 95 E300D water valve life expectancy? Are there any options? Mine's leaking now, not a lot, but one of the tubes is leaking at the base.

Jeremy5848 · #7 04-23-2017, 04:40 PM

The only option is to repair your leaky plastic housing. There's a thread here somewhere that I posted. Get a radiator repair kit from an auto parts house and use the fiberglass and epoxy to make a bandage for the monovalve. It will be much easier if you completely remove the monovalve/pump from the car, take it apart, and clean it thoroughly. However, if you are in time pressure you can do the repair in place. Warning: the radiator repair kit ($20) epoxy sets up in a minute or two, you must work quickly!

My repair is over three years old now and has never leaked. New assemblies are terribly expensive and will also leak after a few weeks—I went through three before repairing my leaky valve and returning it to service. After three years of polite insistence, Mercedes finally refunded the $500 I paid for the first replacement (the others were warranty items).

Jeremy

Maxbumpo · #8 04-24-2017, 11:20 AM

I'd really like to find a mono-valve rebuild kit for 124 cars, both early and later style. Anyone?

chronometers · #9 04-24-2017, 07:12 PM

You can also use the old style monovalve and loop the coolant line. My mechanic did it when I installed a veggie tank in trunk.

The old type is much cheaper and not prone to cracking. You will have some minor flutuations in coolant temperature but in the three years I've been running with one, have never had a problem.

jay_bob · #10 04-24-2017, 08:04 PM

Any chance a W210 duovalve could be adapted? The turbo models have the 4-port design with the bypass feature. The two pots could be wired in parallel, assuming that's not too much current for the CCU driver. Or one pot could be grounded (forcing it closed all the time) and the other connected to the CCU. The CCU has a current limiter so you will know if two pots is too much, it will shut down the output with no damage.

If you can do the two pot solution you could tie the two lines from the heat core to the two valve ports. If the one pot grounded solution is needed then you'd have to Y the valve ports and then re-split to the heat core.

On the 210 switched 12 V dc is applied to the center pin which is common to the two valves, and the CCU grounds the outside pins to actuate the valve as needed.

The 124 is similar but only with one valve. So on your valve harness you'll have to figure out which is the constant hot, that will go to the center pin, the other lead goes to one of the outer pins, and either jumped to the other pin (two pot solution), or ground the other outer pin (if the one pot solution is required).

Just a WAG but it might just work...

Jeremy5848 · #11 04-25-2017, 02:20 AM

That's actually workable, JB, with the caveat that you'd have to install a separate aux pump, because the 124 version is a combined pump/valve while the 210 is valve-only. But it would work, and there are lots of 210 valves around for the picking.

Jeremy