Hey guys, my 2004 s430 is having issues with the heater. First, it will blow hot air at all temperatures except for the lowest temperature setting. So I have to bring it to the lowest setting if I want to use A/C or bring in cool outside air. The A/C works well once it works.

The climate control also only works on lower power settings, the max setting being 3 to 4 levels high before it shuts off. If I put it any higher, it shuts off for a minute or two before turning back on. If I keep it on high, it'll just turn off again. Only if I put it back to low setting will it work.

I've browsed a while and I couldn't find anyone with my similar issues. Has anyone else ever had this issues or know what it might be?

 

I also have the same issue and the same 2004 S430... exactly as you described. Don't have time to troubleshoot the root cause and solutions to fix it yet. The whole summer I set LOW to have AC... just keep the speed on 2-3 bars and it's cold air... manually kept turning the system on and off. Now, it's winter time here in Minnesota, I just turned 1 level up from low (54) and it's heeating up and keep me warm. It's my winter beater car... hopefully, it's ok till next summer and have more time to get it fix. I may not drive it much this winter if this ennoying me too much. Anyway, I love to know any feedback or any suggestion what and how to fix it. TIA

 

Try repairing the hair-thin wire to the thermistor in the upper console.

 

Thanks WallyP. I will look into it.

 

Hello, I have this exact issue on my 2004 S55 AMG. Has a solution been found yet?

@wallyp may I ask exactly which thermistor and location you are referring to?

Thank you,

 

Interior temp thermistor, in the upper control panel, inside the plastic cover above the interior rear view mirror.

 

I just bought this from Ebay and will try to swich out and see if the HVAC woring again:
update: WORKS... Took me about 1 hour (too) carefully swap out with this. If I have to do it again, 15 minutes max. Very simple to unlatch the 4 metal hooks (careful not to break anything else), disconnected 4 wire connectors, reconnected the wire connectors to this used Ebay, popped it back into place and tested... HVAC works normally again.

 

I will post some pics regarding this swap-out the dome light fixture. Nothing fancy... just some pics.
A BIG thanks to WallyP.
Could have done this in the last 12 months... But it's done now and so glad for this cold morning and set auto 71 and temp regulated and control as 71 degrees. So happy.
My next project is to replace the interior temp thermistor of my dome light fixture as WallyP suggested. Hopefully will get some pics.

 

Good job!

 

I opened it up and confirmed the very very thin wire of the thermistor broken, see the pics. WallyP is right... broken wire.

the thermistor inside the fan housing and the wire is broken.

loose these 9 screws, T10.

just 9 screws, and took the circuit board out of the housing. Now, how to solder the broken wire... just about the size of your hair?
TIA

 

Updates:
Overhead console is programed to specified VIN; Scaned with my gerneric scanner showing the code. I don't have MB scanner to reprogram my VIN to it.
Resoldered the tiny thing broken wire and reinstalled back to the car. HVAC system has been working like it should for now. Auto seting is regulating the setting temp.
I don't know if the VIN can be reprogrammed? TIA

 

Confirmed this was the issue with the temperature not regulating properly.

My other issue is that when I put the fan speed on max, the fan turns off completely. I have to put the fan speed back down to low, turn it off for like 20 seconds, then it will work again. But as soon as I turn it back on to max speed, it stops again. Could this be the voltage regulator?

 

Probably the (overcomplicated) blower motor "resistor"

You can find aftermarket ones for cheap.... I see no reason not to except for the usual hesitancy around aftermarket parts.

 

The blower speed is controlled through pulse-width modulation, so there are some complex electronics involved.

 

I keep reading terms like "over-complicated" when referring to different issues when these things are failing after TWENTY SOMETHING YEARS. Consider how long these over complicated parts functioned without any issue.. Old parts on old cars are gonna break and you can cry about it or handle it $.2

 

It turned out to be the voltage regulator. The unit works great now.