Parrot of Doom
MB Enthusiast
Right, as I'm having problems with my aircon (blowing intermittently hot on driver's side) I thought I'd check out the duovalve to see if it was working correctly.
Feel free to point out any stupid errors I've made, but this is what I did:
1) The duovalve from what I understand controls the flow of coolant to the cabin. Obviously you have separate passenger/driver heat controls, so thats why you have 2 valves. On the W210, its located near the brake fluid vessel, offside at the back of the engine bay:
See the two grey cylinders? Thats the duovalve.
2) Start by making sure the coolant isn't too hot. The last thing you want is to open it up and roasting hot coolant comes shooting up your arm, forcing a trip to hospital for burns! First, unplug the power connector. Its a bit stiff, so you may have a bit of a struggle removing it. Its clamped on either side, I used my fingernails to pull the plastic clamps back so the plug could slide free.
3) When its reasonably cool, take a torx bit and unscrew the 5 torx bolts that hold the metal case together:
Don't worry about losing the bolts in the engine bay. They're very long, the reason will be evident shortly:
4) Once the bolts have been removed, you can remove the two covers. They just slide off very easily:
You can now see 2 orange cylinders, not unlike cotton bobs. These are electrical coils, and they're what makes the pistons in the valve move in and out (its the same principle as a hifi speaker). I presume the position of the valve is controlled directly by the position of the temperature dial in the cabin. The two blue components are capacitors, very very cheap and easy to replace. Nothing exotic.
5) Obviously there are 4 large pipes into the duovalve assembly. 2 for water heading in, 2 for water heading out. The duovalve splits in two which makes sense if you have a blockage that needs clearing. Its fairly easy to split, there are no retaining plastic lugs, just plastic guides.
READ THIS BIT CAREFULLY BEFORE YOU SPLIT THE VALVE
At this point, I cannot stress how important it is to have a bit of help on hand. At the very least, a bit of cardboard sheet to stop things falling down into the engine bay.
When you lift the upper half of the duovalve away from the lower half, there are two small valves that are not held in by anything. So what will happen is that if you're not aware they're there, like me, they'll fall out and down into the engine bay! If this happens, to retrieve them either get a long screwdriver with a blob of grease on the end, or remove the cradle that holds the duovalve in place by undoing the bolts on other side of the firewall. You will have the devil's own job getting them out. They're brass and plastic and therefore not magnetic. Its easy to do with a grabber, but guess who didn't have one....
Anyhow once I'd retrieved them, this is what they looked like:
6) Theres not much else to do here. Check all the pipes and the valve body, make sure there are no obvious blockages. Give everything a wipe, remove any rust and crud. If you want to remove the rubber pipes its easy enough, just take a pair of mole grips and squeeze the clamps open, slide the clamp back away from the duovalve, then put a large flat bladed screwdriver in the end of the hose to free it before you tug it off the duovalve body. Might be an idea to get the help of a friend here since putting the clips back on can be tricky, there are a few bits of engine bay that get in the way.
7) I used an anti-fling spray oil to lubricate the pistons on the valve. The pistons are the only moving part visible unless you were to take the entire thing to bits. Its all pressed metal and plastic so I didn't think it would be a good idea to do that, especially when dealing with water and seals. Fortunately both pistons moved pretty freely on mine, they do make a slight grating sound as they move up and down, and they are spring-assisted, but I'm presuming thats normal.
8) To put the duovalve back together, the easiest thing is to put the two loose valves in the lower half on the duovalve body, and very carefully slide the top half of the body down so that the valves mate with the pistons correctly.
9) The rest of reassembly is the reverse of the above method. The power connector only fits one way, but even if you manage to connect it the wrong way all that should happen is that the heating controls in the cabin will be crossed over.
10) Use a hose and clean tapwater to carefully wash around the duovalve and any places that antifreeze spilled over. Its icky stuff and doesn't really dry too well, you don't really want it gumming up your engine bay. Take care not to get water down the numerous electrical connections that are in that area of the engine bay.
Feel free to point out any stupid errors I've made, but this is what I did:
1) The duovalve from what I understand controls the flow of coolant to the cabin. Obviously you have separate passenger/driver heat controls, so thats why you have 2 valves. On the W210, its located near the brake fluid vessel, offside at the back of the engine bay:
See the two grey cylinders? Thats the duovalve.
2) Start by making sure the coolant isn't too hot. The last thing you want is to open it up and roasting hot coolant comes shooting up your arm, forcing a trip to hospital for burns! First, unplug the power connector. Its a bit stiff, so you may have a bit of a struggle removing it. Its clamped on either side, I used my fingernails to pull the plastic clamps back so the plug could slide free.
3) When its reasonably cool, take a torx bit and unscrew the 5 torx bolts that hold the metal case together:
Don't worry about losing the bolts in the engine bay. They're very long, the reason will be evident shortly:
4) Once the bolts have been removed, you can remove the two covers. They just slide off very easily:
You can now see 2 orange cylinders, not unlike cotton bobs. These are electrical coils, and they're what makes the pistons in the valve move in and out (its the same principle as a hifi speaker). I presume the position of the valve is controlled directly by the position of the temperature dial in the cabin. The two blue components are capacitors, very very cheap and easy to replace. Nothing exotic.
5) Obviously there are 4 large pipes into the duovalve assembly. 2 for water heading in, 2 for water heading out. The duovalve splits in two which makes sense if you have a blockage that needs clearing. Its fairly easy to split, there are no retaining plastic lugs, just plastic guides.
READ THIS BIT CAREFULLY BEFORE YOU SPLIT THE VALVE
At this point, I cannot stress how important it is to have a bit of help on hand. At the very least, a bit of cardboard sheet to stop things falling down into the engine bay.
When you lift the upper half of the duovalve away from the lower half, there are two small valves that are not held in by anything. So what will happen is that if you're not aware they're there, like me, they'll fall out and down into the engine bay! If this happens, to retrieve them either get a long screwdriver with a blob of grease on the end, or remove the cradle that holds the duovalve in place by undoing the bolts on other side of the firewall. You will have the devil's own job getting them out. They're brass and plastic and therefore not magnetic. Its easy to do with a grabber, but guess who didn't have one....
Anyhow once I'd retrieved them, this is what they looked like:
6) Theres not much else to do here. Check all the pipes and the valve body, make sure there are no obvious blockages. Give everything a wipe, remove any rust and crud. If you want to remove the rubber pipes its easy enough, just take a pair of mole grips and squeeze the clamps open, slide the clamp back away from the duovalve, then put a large flat bladed screwdriver in the end of the hose to free it before you tug it off the duovalve body. Might be an idea to get the help of a friend here since putting the clips back on can be tricky, there are a few bits of engine bay that get in the way.
7) I used an anti-fling spray oil to lubricate the pistons on the valve. The pistons are the only moving part visible unless you were to take the entire thing to bits. Its all pressed metal and plastic so I didn't think it would be a good idea to do that, especially when dealing with water and seals. Fortunately both pistons moved pretty freely on mine, they do make a slight grating sound as they move up and down, and they are spring-assisted, but I'm presuming thats normal.
8) To put the duovalve back together, the easiest thing is to put the two loose valves in the lower half on the duovalve body, and very carefully slide the top half of the body down so that the valves mate with the pistons correctly.
9) The rest of reassembly is the reverse of the above method. The power connector only fits one way, but even if you manage to connect it the wrong way all that should happen is that the heating controls in the cabin will be crossed over.
10) Use a hose and clean tapwater to carefully wash around the duovalve and any places that antifreeze spilled over. Its icky stuff and doesn't really dry too well, you don't really want it gumming up your engine bay. Take care not to get water down the numerous electrical connections that are in that area of the engine bay.
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