HEATER FAN SPEED CONTROL (manual climate control)

[r44raven]

The heater fan control on my 1993 500E (European delivery model) now only operates on position 1 and 4. At 3 & 4, there is nothing!

Am I right in thinking this is unlikely to be a fault with the control on the dash facia itself - but more the fault of some bit of electronic gizmo buried somewhere either behind the dash, or in the engine compartment? (I only say this, because a similar problem on my 2006 A Class was nothing to do with the control knob, but some other bit of wizardry hidden away somewhere?).

Can anyone help me with what I should be looking for?

Thanks in advance!

 

[nocfn]

So you have power (no blown 30 amp fuse) and the fan work on speeds 1,2 but not the higher fan speeds, is that right. I think you can test the volts coming off the Push button unit (PBU) on the wires coming into the firewall. It typically is either the Push button unit (do you have a spare?) or the resistor at the fan.

 

[r44raven]

So you have power (no blown 30 amp fuse) and the fan work on speeds 1,2 but not the higher fan speeds, is that right. I think you can test the volts coming off the Push button unit (PBU) on the wires coming into the firewall. It typically is either the Push button unit (do you have a spare?) or the resistor at the fan.

Not quite sure what you mean when you say "Push button"? My heater fan control is a rotary knob (do some cars have push buttons?). I attach a pic - it actually it works on positions III and IIII, but not on I and II). Anyhow, what we are saying is that the problem could either be this knob, in which case I need to try and somehow test the voltage coming from it - or the resistor, which I believe sits on top of the fan? And if the latter needs replacing, this would entail a substantial amount of dismantling of the front console to access it?

 

[gsxr]

Automatic Climate Control (ACC) has pushbuttons only, zero knobs. ACC only offers fan speeds of Min, Auto, and Max.

The systems are radically different. MCC does not have a blower speed regulator like ACC does. I've never owned any car with MCC but from what I understand the speed controller is a resistor pack of some sort, not a solid-state regulator?

Unfortunately I know nothing about how to diagnose MCC systems... sorry!

 

[r44raven]

Automatic Climate Control (ACC) has pushbuttons only, zero knobs. ACC only offers fan speeds of Min, Auto, and Max.

The systems are radically different. MCC does not have a blower speed regulator like ACC does. I've never owned any car with MCC but from what I understand the speed controller is a resistor pack of some sort, not a solid-state regulator?

Unfortunately I know nothing about how to diagnose MCC systems... sorry!

OK - thanks! I guess the ACC were mainly for the North American market, and the MCC for Europe. I've got a pretty good MB indi here where I can ask some advice. Just initially thought it might be DIY'able!

 

[gerryvz]

OK - thanks! I guess the ACC were mainly for the North American market, and the MCC for Europe. I've got a pretty good MB indi here where I can ask some advice. Just initially thought it might be DIY'able!

ACC was considered the "high end" option for Euro/ROW cars. It is definitely found on SOME Euro cars, but is not nearly as common as MCC there.

It was standard equipment on every MBUSA-imported E500E officially brought into North America. It is also often found on Japan-market E500Es.

 

[nocfn]

GOT it, sorry!