ssfisher

The rear ac comes thru venting on the driver and passenger doors. There is no separate controls for the rear. 2001 s500 w220. There are two plugs at my duo valve. One plug has two wires and it connects to the reserculating pump. (I think its a pump?) The other connector goes to both small solenoids. (Left and right heat control solinoinds) The connector with two wires has 2.8 volts when the car is running and set to auto and lo settings on the climate control.

DrDoe

Do you see the 3 pins? Voltages between 1-2 and 2-3?

ssfisher

Yea, pretty much zero volts. Between 1&2= 0.03 volts 2&3= 0.01 volts. That never changed and i went from auto Lo to auto Hi to manual Lo and manual Hi. Where is the power supposed to come from? Thanks Dr.

ssfisher

Also i just read the duo valve function info that you posted a few post ago, and that talks about rear ac button and controls. I dont have rear ac. The rear ac blows thru ducts in the driver and passenger doors and out vents on both "B" pillars. There is also ducts and vent in the center console that blow in the rear. Here is are the last 7 of my vin A161440

DrDoe

Sorry to add to the confusion. The function of the duovalve is the same for front and rear. The location is not. Ignore the word rear and that screenshot would tell you the function of your front duovalve.

DrDoe

Perhaps others can chime in on the voltage readings. To me the voltage is about the same for both valves and you replaced the unit already. I would look elsewhere for left and right to swap.

ssfisher

Also the two wire connecter on tbe duo valve only has 2.8 volts. I would think it should be 12 volts? Its like whatever controls that whole system is not doing its job, but i dont know what sends the voltage. Is it the left SAM?

DrDoe

Why would 12v or 2.8v effect the left and not the right?

ssfisher

I dont think it would effect it, but im guessing its powered by whatever powers the solenoids making me think that something "big" or like a computer is bad, not just a left or right sensor or left or right door or something like that.

kraut56

The 12v for the recirculation pump only makes it work when commaned, which is not often (eg: pushing the REST button in the heating mode, or automatically during engine warm up and hot engine shut-down).

The solenoid valves only work for ac, so one is stuck open, and you should troubleshoot that further by taking the solenoids off and inspecting the valve spool.

Do it for practice on the old one first.

You may have to reset the ac system, but, if it work on one side that may not be necessary.

As a hint: check the ground (negative) pins for resistance.

Good luck!

ssfisher

Roger that. I pulled the old one apart before i changed it. I will take the replacement one apart tonight. Ill also check the resistance. Thanks. Ill report back late tonight

ssfisher

Well didn't get anything done last night. Ended up at work late. Should get some answers tonight. Thanks for everyone's help with this. Ill report back again tonight or tomorrow morning.

ssfisher

Pulled duo valve solenoids apart, inspected and cleaned both sides. They didnt look gummed up or bad at all. Reasembled them. Checked for good ground and it was. No issues noted. Still hot on drivers side and cold on passenger side.

kraut56

Good, you checked the grounds; what's the voltage on either solenoid plug?

ssfisher

The voltage on the 3 pin plug between the two solinoids is as follows: Pin 1 = .03 volts. Pin 2 = ground. Pin 3 = .02 volts.


The voltage at the 2 pin plug on the resurculating pump is as follows: Pin 1 = ground. Pin 2 = 14.08 volts. Between pin 1 and pin 2 = 2.8 volts.

wallyp

"The voltage at the 2 pin plug on the resurculating pump is as follows: Pin 1 = ground. Pin 2 = 14.08 volts. Between pin 1 and pin 2 = 2.8 volts."

While I don't believe that the recirculating pump has anything to do with your problem, I don't understand that.

If Pin 1 is ground, and Pin 2 has 14vdc to ground, there must be 14vdc between Pins 1 and 2.

How did you determine that Pin 1 is ground? Did you measure zero Ohms between Pin 1 and a good body/chassis ground?
How did you determine that Pin 2 has 14vdc? Did you measure 14 vdc between Pin 2 and a good body/chassis ground?

ssfisher

Yea, thats a type "o". Didnt go from paper to computer the same. Ill check my notes after work tonight, but i know Pin 2 to ground is 14 volts and between Pin 1 and 2 is 2.08 volts, but dont remember what Pin 1 to ground was. Ill re post tonight

kraut56

you have not established WHY one solenoid valve is open, and the other one is closed when in AC mode. There is no other explanation for the symptom.

As suggested before, if you clamp the hose of the "hot" one, your AC should work fine.

The voltage check should be done in both heating and cooling mode (and don't forget that the HAVC system takes a while to actually normalize after you start the car - part of "profiling" the generator load).

Good luck!

ssfisher

Yea i am still trying to find why its not working. Everyones help is great. I appreciate it alot. I will clamp off the hose tonight and check in both heating and cooling modes and get the pin 1 to ground info. Thanks

ssfisher

Ok, two pin connector test results: Pin 1 to chassis ground = 0.0 vdc. Pin 2 and chassis ground = 14.08 vdc. Pin 1 to chassis ground shows open.

ssfisher

On a side note....i clamped the hot hose and at least its not blowing hot air inside now, but that is only a temporary solution. I still need to figure out what is broke. Is there a way to test the climate control head unit? It may say LO on the display but maybe its not sending a signal to actually make it LO?

kraut56

you are getting somewhere!

You now need some electrical schematics; (I believe) the HACV control panel uses the CAN bus to a SAM, and from there to the duo valve.

Good luck!

wallyp

If I understand your posts so far, you are testing the electrical contacts on the
duo-valve. You got sidetracked on the recirculating pump, but htat appears to be cleared up now.

You have two solenoid-operated valves that control the coolant flow to the left and right sides of the HVAC. Valve open = coolant flow = heat. Valve closed = blocked coolant flow = no heat.

You have heat on the left, and not on the right. You have checked the voltages to the valves, and both valves appear to be getting close to zero voltage.

Since the system is set to cool the interior, and the right side is cool, it seems to be a reasonable assumption that the valves are NC (Normally Closed) and opened by 12vdc. I would immediately check this on the spare duo-valve, by blowing thru the valve with no power connected, then connect 12vdc to the valve and try blowing thru it again. Check both sides!

If the valves are NC, then the control system is working, and the problem is in the duo-valve OR in the way you are reading the voltage, OR the control system is smart enough to not apply voltage with the valve unplugged.

If the valves are NO (Normally Open) then you should have flow thru both sides with no power applied. This is usually the default for a German HVAC system - if the system fails, you still have heat, primarily for windshield defog/defrost.

If the valves are NO, then the control system is not working while you are testing the voltage, and the problem is in the way you are reading the voltage, OR the control system is smart enough to not apply voltage with the valve unplugged.

I would connect the spare duo-valve to the car harness, and test the flow and the voltage. Get three short pieces of some very small solid wire and insert one piece into each of the connector terminals. Check the ground terminal to make sure that it is really ground. Check the voltage to that terminal on each side with the valve functional in the circuit.

If the voltages are the same for both sides at all times, then it would appear that the control system is working. Blowing thru the valve should complete the test.

While it is possible that the system might be set up to require different voltage on each side for proper functioning (one side NC, one side NO), I consider that to be highly unlikely.

You can repeat the testing with the installed duo-valve, feeling the coolant lines rather than blowing thru the valve.

ssfisher

I do not have access to any wiring schematics, but i can perform the test by blowing thru the old one and checking voltage thru it and the one installed while pluged into car and running. I will do these test this afternoon and post my findings. Thank you all for the help and ideas!

kraut56

I have on my desk 2 duo-valves, and they seem to be identical electrically an functional.
The solenoid coils are 21.6 ohms on all.

It gets a bit more complicated when you blow thru the ports; follow the arrows in the tubing block. The solenoid valves are open when unpowered, but there also appears to be a check valve involved with the recirculation pump. It appears the solenoid valves block off the RETURN flow.

At this time can somebody find a diagram for the coolant flow to the heating system for this car?