Duovalve tick ticking

[KLee]

Right quick question regarding my duovalve (also known as heater valve). When engine is hot (85 deg C) and temperature selector dial is turned fully Blue until it clicks, there is a loud and unmistakable tick tick tick from the 2 duovalve cylinders. I can feel the ticking vibrations greatest when I touch the pipes into the duovalve (the cylinders itself is too hot to touch). When I turn the dials towards White or just take it slightly out of fully Blue, the ticking slows down (longer intervals) and eventually stops. Someone mentioned its the solenoids ticking - is this normal? Is it struggling to completely shut the valve to prevent hot coolant from entering the cabin heater? Does this mean its on the way OUT?

Some background: my radiator has been completely replaced with a new unit (core and expansion/header tank). AC wasn't working but now fixed (1 relay and 1 fuse so no major component replaced). Blows cold but not like a Jap car though so I'm starting to get concerned it is being hampered by hot coolant getting to the cabin heaters and affecting my AC coldness.

 

[Ian B Walker]

In all probablility your duo valve is on its way out, sorry to be the bearer of depressing news. However they are not difficult to change.

 

[KLee]

That is depressing. Would keeping the temp selector at positions that stop the ticking mean I am helping it positively or just masking it? If a clean out does not succeed would a used part be acceptable or not worth the trouble down the line?

 

[c13tay]

Mine has done that for years !!!!

 

[KLee]

Mine has done that for years !!!!

Really? Thats encouraging that it can tick tick away and not pack in yet. So does anyone have any idea what is causing the ticking sound? I imagine the valve shutting off the hot coolant operates like the household water tap with some motor doing the turning? If so, is it ticking because it is repeatedly trying to close, but isnt and keeps trying? Stuck?

 

[c13tay]

Dont know but it stops totally on mine if I turn the fan off completely

Temp function seems to be ok

 

[Dec]

You could try giving the duo valves a bit of exercise by turning the heater dials from cold to hot for a 5 minutes then back from hot to cold for another 5 minutes, repeat this procedure as often as possible while driving for a couple of days. This might loosen up the valves and stop the ticking. I imagine where you live you seldom have your heater on hot. You should also check that the electrical connections at the valves are good. Worth a try costs nothing.

Dec

 

[KLee]

Yeah I have been doing a bit of something similar to that. Will continue doing it. In the MB user manual it actually says to set the temp selector dial to White for basic summer cooling. It never mentions anywhere to turn it until locked to Blue. How curious.

 

[Dieselman]

The valves tick because the voltage applied is always 12v (I think). The percentage of time in the on/off cycle is how they regulate the hot water flow.

 

[reflexboy]

Mine has done that for years !!!!

Same here-Its done it for the 2yrs I have owned my car too,but all the heating and A/C controls work fine-I thinks its another 'qwerk' of these cars.

 

[KLee]

Whist driving have been playing around with the temp dials. All seems to work ok, touch wood. Perhaps mine has also been ticking all the time ... reflexboy, is your AC factory or aftermarket eg Diavia?