W210 heater only blowing hot

[markb_b_uk]

Hi all I'm new here! I have a 1996 E320. No matter if the temperature control is set to cold or hot it only blows hot air. This isn't ideal with the warm weather lately. Anyone got any suggestions on how to rectify this? I've been scanning through other threads. Is the duo valve the first thing to check? Or could it be a bad relay? Any ideas anyone?

 

[television]

The first thing to check is the duo valve, and they fail in the hot mode. The is a post on fixing these in the DIY section and on a 210.

Welcome to the forum

 

[markb_b_uk]

ok I'll try that and let you know the outcome!

 

[bigshineybike]

I have a W124 estate. I have hot air at all settings except fully off.
I have the duo valve in bits.
Watch out if you are doing this since the screws snapped off when i put it back togehter.
It is all working fine nice and clean inside all wires good nick. I know this part hasnt been changed as I have FULL service history for the car.
So what else can be wrong?
I have had the control unit out of the dashboard.
This is within the panel on the Dash which you access when removing the heater dials.
Do these ever fail?
The printed circuit board has a sort of white film over most of the soldered joints, I am thinking its corrosion.
In my search of many forums thousands of pounds are being spent on Duo Valves but never this dodgy looking bit of electronics.
I do seem to be reading 12volts into both duovalves but not all the time and there seems no change between hot and cold settings.
I am going to try puting a bulb across the terminals to see if its a trick my multimeter is playing.

I am not going anywhere today there is a steel tube in the radiator hose (down under the air filer) that has decided it wants to become a garden sprinkler! Too much fiddling on my part!

 

[television]

Yes the output from the control unit is a pulsed output, a lamp would be an ideal way to try it,,the duo valv needs the full voltage to get it to the cold mode.

If the voltage was a fixed voltage,,the solenoid coil in the valve would get hot