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Climate Control-one sided heat

1589 Views 8 Replies 4 Participants Last post by  mannfrm
Good Morning-

Texas weather has been nice till this week when we got our first freezing temps.
My 1994 w140 climate control was not up to heating the cabin sufficiently. I ran the sensor value test.


est Step Sensor Value Display
1 73 In-car temperature sensor w/ aspirator blower (B10/4)
2 72 Outside temperature sensor (B10/5)
3 86 Left heater core temperature sensor (B10/2)*
4 87 Right heater core temperature sensor (B10/3)*
5 35 Evaporator temperature sensor (B10/6)
6 87 Coolant temperature sensor (B10/8)*
7 11 Refrigerant pressure in bar (06 = 6 bar)
8 14 Blower control voltage from B(min) - 60(max)
9 20 Software status

Also, performed flap test and found 3 to 4 of primarily driver side flaps did not seem to operate by ear. So, I turned heater on and checked both sides of compartment for air flow. I found that I was not receiving heat from most driver side vents and if any air flow was found, it was non-heated air. Passenger side vents were operating and I could feel heat. Turned on the red button on center vent and received heated air on passenger side but none on driver side.

My questions are:
-the above sensor values look correct except #5. Do I have a evaporator sensor out?
-Is the non-performing driver side attributable to a non-functioning duo-valve or possibly a Y11 vacuum block malfunction?

Those are my questions from reading through the archives. Any help will be appreciated.

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maybe evaporator sensor is slightly non-accurate but it is always ok to be between 3 -6 °C when AC is on.

35 °F = ca 2 °C

but evaporator does not have much connection with heating so forget it for now. First thing which i would do is HVAC self test (find instructions in this forum under advanced search). then write down all errors (if any) and delete them. turn on the car for several seconds, turn it off and repeat the test and see which errors are present now. these are reliable.

most probbaly your duovalve is bad. if you will get an error for it then you know it is time for new one.
When I had one sided heat I replaced the Duo-Valve and it fixed my issue.
This is reasonable. In addition if temperature sensor makes problems it is very cheap to replace it. So in your place i would replace duo valve and test temperature sensor. There are three of them in my car, so make sure you will test the right one. Briefly, it has two pins and you should measure different ohm impedance at different temperatures. Roughly it is ca 200 ohm for warm engine and several kohm for cold one.

you can also test your duovalve impedance. it is hard to test it mechanically unless you open it.
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