may not be right thread, heater probs

[mercjim]

ok... heater is warm constantly... wont turn up or down with either control nobs....

its not red hot... but when driving distance... need to have either sun roof on tilt open or a window slightly down to relax the heat....

any ideas?

thx

 

[230K]

hi

Check your fuses, but most likely your duo valve. It can be cleaned and can be a success but you could end up needing a new one.

230k

 

[coupe deville]

hi black bettys new daddy welcome-- 90% its the duo valve, I did mine and now got perfect temp control. do a search for duo valve and read THE PARROT OF DOOMS POST-great post with pictures and although my car is a different model to his its still basically the same. I found it easier to take it out of the car to clean. dont use any oil or grease to free it. use something like servisol aero klene 50 from maplins electronics

 

[mercjim]

awesome post by parrot of doom.... thx guys

 

[KillerHERTZ]

ignore, I didnt read all of the replies doh!

 

[mercjim]

ok, cleaned duo valve out.... lots of residue in there....
put it back together b4 a long trip from leeds to birmingham.....
was exactly the same...
so gonna open it up and see if there is more residue in there...
thinking about flushing the entire system tbh....

any more ideas?

thx

 

[KillerHERTZ]

Early W202s are prone to having the heater control unit fail.

Does your heater dial go up to 4 or the later 5?

I had exactly the same problem, it turned out to be the dash control unit.

 

[mercjim]

4 with the window demister on it....
totally flushed the system... and still same...
doesnt matter if i have the controls on cold or red hot...
still filters warm air thru.... no cold, no hot...

thx for help

 

[alibally]

Will the temp change when clicked into either full hot or full cold? If it does and the heater won't regulate in between then the ambient cabin temp sensor mounted in the interior light unit may be faulty.

 

[mercjim]

its the same temp all the time bud... no matter wether i have it on hot / cold... full blow or off.....

 

[alibally]

Unplug the duo valve a see if it goes red hot. The valve should go to fully open if you do this. You could check the voltage at the duo valve. Thers should be a 3 pin plug . The center pin is a ignition live and the outer of the pins are a switched earth from the heater control panel. With the heater on hot there should be 0 volts. Full cold you should get 12 volts. A test light can also be used. the light will be off at full hot, on at full cold and if the temp controls are set to the middle it will flash on and off. If this all works fine then the heater control panel will probably be ok..

 

[mercjim]

ok, thx again Alibally... tried the above with a 12 circuit tester, nothing... nada....

does this mean the control panel is kerplunkt?

all fuses ok... only thing that seems to work is the heater fan control knob.... & the heat directional knob

 

[vijilants]

The duo valve is fed directly from the control panel.