DrDoe

Is this what you are looking for?

kraut56

Yes! This confirms that that the duo-valve controls the return flow from the heater, so one must be open incorrectly when in cooling mode.

A question for ssfisher: has the car always had this fault since you got it?

If so - maybe the hose connections are wrong, but, electrical more plausible otherwise.

ssfisher

Negative, it was working when i got it just over a year ago.

kraut56

we need the electrical schematic for your cars HCVA system to find out the relay location on which SAM. As far as I know the control panel only communicates via CAN bus.

DrDoe

What's the values of NR.30 and NR.31?

ssfisher

It goes from NR.29 to NR.40. No NR.30 or 31

DrDoe

Are you holding the REST with key on #2? I don't understand why you don't have 30-31

ssfisher

I used the rest button, but the car is moving. I dont think that matters tho?

ssfisher

The duo valve i removed from the car i just tested on the bench. Each coil has 21.5 ohms resistance and each coil operates when power is applied

wallyp

Does the coil operation block air flow through that side of the valve?

ssfisher

Yes, both sides block air with power on the coils. So since the one on the bench and the replacement one in the car both did not close one side, it is telling me its not the valve.

ItalianJoe1

Yeah sounds like you have a control issue.

They click shut right? As soon as you apply power it's closed? That explains your voltage readings, they are PWM solenoids, so the low voltage one is trying to stay mostly open, it's barely pulsing the power on so you're getting <3v on that side.

Gotta be a control unit or temp sensor issue. I'd think if there was a shorted temp sensor you'd be getting error codes for it, the only way it would run heat with the controls set to "LO" should be if there's a controller fault, as on that setting it should be max cooling regardless of internal temperature settings.

ssfisher

Yes, it shuts as soon as power is applied. I swapped the two temp sensors left to right and still had the same issue on the same side. I dont have another control unit to plug in and try. Does anyone know if i can test the one in the car somehow if i put it on the bench?

DrDoe

I don't think you swapped the left and right heat exchanger temp sensors. The location was posted earlier.
NR.30 and NR.31 are those heat exchanger readings.

ssfisher

Which ones did i swap then? The onez i swapped are located behind the radio. They are a two wire plug and very small.

ssfisher

The ones i swapped are associated with NR. 03 and NR.04

DrDoe

I believe we switched cables but we didn't swapped sensors

ssfisher

Yea, we swapped cables and the high reading went from NR.03 to NR.04 so that tells us the sensors are good because the high temp went from left to right.

evenfall

I know this thread is old but I was wondering if the OP has eventually found a solution to the issue. I am having the exact same problem, the heater blows very hot regardless of the temperature setting except when in LO mode. The duovalve has been replaced, did not have any effect. So far I have not been able to find a report of anyone resolving this issue on any of the forums. Would appreciate any suggestions. Thanks!

ssfisher

As of now it's still broke. We never found the issue. It still drives me crazy. I have been using a plastic hose clamp on the hose that stays hot. I clamp it when it's hot out and in clamp it when it's cold. Mostly it has been clamped for the last few months as I live in Colorado. There was alot of good troubleshooting and suggestions made by several people and I checked and tried all of them but we never have found the problem and I stopped looking into it. I wouldn't mind starting up again to resolve it tho..

DrDoe

If it blows hot except for LO setting then the issue is with the temperature sensor. The unit is inside the center ceiling unit.

ssfisher

I guess his issue is different than mine. Mine blows hot always, no matter what setting. I believe your correct in saying it's the temp sensor if it works on LO. Wish mine was that easy

evenfall

Sorry I must have missed that the OP issue is that it blows hot at all times. It is not as much problem for me during the warm season since I can always set it to LO and everything functions as it should on that setting. Thanks for the tip about the temp sensor! I will pursue that direction. I also posted on the w220 UK forum and that thread had an issue identical to mine where it works fine on LO, no definite resolution there. Thanks again.

DrDoe

No problems. I got the 04 S430 few years ago and I didn't know that it was a problem until someone pointed that out for me. I opened it up and saw the broken wire right away. Re-soldered and it has been working fine since.
If you go through the voltage diagnostics you will see 0 readings for the open circuit. The climate system see 0 so it try to compensate with heat.

evenfall

Is part number 2108300072 correct for the cabin temperature sensor? It is part #14 in this diagram:

https://www.oediscountparts.com/medi.../5/5891070.gif

does not look like it is in the ceiling assembly or is it the same part in both? This is all I've been able to find after searching multiple vendor sites.