Is a Heater Supply Unit the same as a Duovalve?
 

All,

Thanks for listening! I'm having heating problems with my 93 500 SEL. The DTCs are:

E0 74 Heater supply unit circulation pup (A31m1), open or short circuit *)
E0 75 Heater supply unit circulation pup (A31m1), open or short circuit **)
E0 83 Heater supply unit left duovalve (A31y1), open or short circuit **)
E0 87 Heater supply unit right duovalve (A31y2), open or short circuit **)

Can someone tell me if the heater supply unit and the duovalve are the same part? Do they come together, or can they be replaced separately? I'm a newbie, and I need some help please!

From references it looks like the HSCP A31m1 and the duovalves are separate componants, they are (3 units)clustered together on the drivers side fender well or engine. They look like three small tin cans. A31m1 is larger than the duovalves

Wires are for HSCP (brown&green wire) and a (grey &red) the 2 duovalves have what appears to be 3 wires going to them a (brown&red) a ( grey&red from HSCP) and a (brown&purple).

They can be replaced separately. But you might check the connections/function before replacement.

Inspector1,

Many thanks! I chickened out and took it to the inde shop that I deal with for them to replace. I did give them the dtc codes so they could get the part in before my car arrived. Hopefully, and new HSCP will give me back some heat. I don't really need it now, but come November it can get pretty cold here!

Thanks again for the top notch help. The decription was dead on!

an update
 

Hey Inspector1,

I took the car to my inde shop to get the heating situation checked out. The MB guy there seems to think that the HSCP and the duovavles are all one thing. They replaced the duovalve and told me it was fixed. However when I went to pickup the car it still has no heat. How sure are you that the HSCP can be replaced seperately? I don't want to go back up there and cause a scene if I'm not really sure that they are wrong. (although the empirical evidence would suggest just that!)

I am going by reference material sa I am not familiar with your specific vehicle, i will try to find time today to check this out.

if we are talking about a31ml,also called aux. water pump, yes,the pump can be replaced separately, there are four screws at it's base that hold it on the housing for the duovalves. Time for replacement as per ALLDATA is only .8 of an hour.