Can anyone tell me why my 98 ML 320 (160,000 Mi)will switch to heat out
the vents for no apparent reason ? The AC is workilng proberly, and the
compresson is running and cycling properly. However since the problem started, the temp at the vents is not as cold as it use to be (65degrees)
The Evap. in at the cabin filter is very cold. What appears to be happening is that the heat valve, or blend door is switching at times.
This only happens after the engine is warm, and then only some times..
Is there a heater control valve or vac. operated valve that controls this?

JMylin;1246404]Can anyone tell me why my 98 ML 320 (160,000 Mi)will switch to heat out
the vents for no apparent reason ? The AC is workilng proberly, and the
compresson is running and cycling properly. However since the problem started, the temp at the vents is not as cold as it use to be (65degrees)
The Evap. in at the cabin filter is very cold. What appears to be happening is that the heat valve, or blend door is switching at times.
This only happens after the engine is warm, and then only some times..
Is there a heater control valve or vac. operated valve that controls this?]

Welcolme......


The early ML uses a blend air system..no heater valve. Also no diagnostic abilities on that early system.

There are 4 possibilities for your problem..YOU will have a hard time trying to figure out which one will rectify the problem.

The in-car temp sensor
the control unit in dash
the blend air motor &
the blend air control unit.

ANY of those could cause an intermittent problem like you are having.

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