ThienNguyen

Hi all, please give me some advice on what to look for . My 1997 S420 has no heat. Blower works fine and aircond is ok.
Appreciate any help.

benica

Duo valve. Driver's side under the larger plastic cover/fender.
If it's an electrical issue...then taking it apart won't help...mine was not an electrical problem with the duo valve...it was just corroded.
I took my duo valve apart....the smaller "tin cup housing" has a magnet in it and an impeller/fan blade type. I sanded it down...had metal build up/ridges on it... smooth them out, sanded the inside of the magnet housing and reinstalled. Next, removed the duel (2 cup housing) housing...took out the small brass "nipples," they were corroded...sanded them, cleaned up the inside where the "nipples" are housed and the rubber seals..reinstalled...added coolant, fired up the engine...a few minutes later...heat! I used 1000 grit paper.
I experiment on another duo valve first...got it at the bone yard. Now I have a back up for the future.
If yours has an electrical issue....this won't help you. You'll have to test the connections making sure you are getting power first.

ThienNguyen

Apreciate the advice, Ben. Will give it a shot... many thanks

ThienNguyen

Ben, I did open up the duo valve for inspection and found no major debris or corrosion. I did clean up and checked continuity on both valves. They're fine. The 2 outside pins are ground (-) and the middle pin is hot (+) according to the power connector where the middle pin either outside pin will give a 12v. One thing I noticed that after running for about half an hour, the 2 hoses out of 4 are not hot at all ? That made me wonder if the heater cores is the culprit ?
Thanks for your advice so far.

jemfrap

sounds like the heater cores

benica

I am not sure about the hoses you mentioned.....2 hot...2 not.....you have the main hose which of course feeds the duo valve and the others hoses are the out-put....you have power obviously....sounds like the valve is not opening up completely to release water...you might have a restriction in the system/heater core.....but with 2 of the hoses hot....I would not think a restriction is the problem.
If you are able to get a used valve from the junk yard....it might be the way to go.....
I'm no expert and my problem was fixed by opening the valve up and cleaning it up...lucky I guess....
but even though you have power....the power may not be opening up the valve completely....90% of the time with W140's...your problem......has been the valve.

xrobk818x

hello everybody , i bought a 1997 s500 today and need some help with the heater. a/c on works perfect, but when you turn the heater on nothing blows threw. the center buttons up top dont even light up the hot/cold switch between the vents , what should i look for does anyone know .... please help

ThienNguyen

Sorry for the confusion on my post. As i recalled and the more i looked at the picture of the valve. The 3 hoses (2 at the bottom (input to heat exchanger) and 1 at the top (return from heat exchange) weren't warm at all. The one at the middle (output from the valve) and the one hose at the bottom of the pump (input to the valve) were the only ones warm . One thing I didn't do, while I had the valve in my hand, was to apply the voltage to the valve to see if it does actuated (grr...!!). Another thinnking was if the heat exchanger does clog up then there will be no flow ?. I'm planning on to flush water to the heat exchange to see what the flow is looking like w/o tearing deep to its location.
Thanks again, Ben

ThienNguyen

I decided to removed the duo valve assemble and gave it a thorough inspection. There was no obvisous issue visually. I did some good cleaning around the actuators areas of the valves. While having the assembly on my hands , I applied 12v to the pump motor and the 2 valves. All are working as expected. I re-installed the assembly, started up the car and within 10 minutes i can feel the 3 hoses started get warm. The heater is now working.. I can only say somehow the valves were stuck . Thanks for all the advices folks.