A/C fan speeds up from time to time

[486]

Latterly my A/C fan speeds up for 1-2 min and restores to normal level. Everything with A/C was OK until this spring. One time the fan stopped for 10-15 seconds, then run with normal speed. After about a month it happened again. It has not stopped for 1-2 months but since recently several times per week happens the speed-up problem. Is it possible that the reason for this behaviour is the temperature sensor (with small fan) near the lamp? If it gives unstable and unreal temperatures, the fans will speed up and restore. For example 24-25-24°C, then 35-36°C, then again 24-25°C. Can I read the values of interior temperature from OBD?

[Doggy]

The interior temperature sensor gets blocked up with dust etc. worth cleaning it out
viewtopic.php?p=83025#p83025

[486]

It seems the problem is in (1) or (2) in the following scheme. But I cannot understand how to access the sensors - is it necessary to remove A/C control panel (above CD audio) or they are accessible in other way?

[486]

My old problem started again. I am nearly sure that sensor 1 (evaporator) is the reason. Last year I replaced it and this solved the problem. What can be the reason such part to stop working again?

[Doggy]

I think it's unlikely to be the sensor twice. More likely corroded connections under the carpets in the drivers footwell, or something similar.

Do you still have the old sensor?, (worth comparing them).

As it's a 2-wire temperature sensor,it will very likely be a thermistor of some sort. Try measuring the resisitance between the pins. No idea what it should be, but probably something between100 to 10000 ohms. It should not be zero resistance or open circuit.

It's intended to measure temperatures between roughly -10 and +40 degrees, so should have a noticeable change in resistance if you were to put it in your freezer for a time, then measure as it warms to room temperature

[486]

First time, 5 years ago, it failed after several ignition attempts (frozen fuel). Next time (2020) I think it was similar - low battery before alternator refurbishing. But this year I don't remember low battery / eco mode warning. It sounds like impossible connection between low voltage and temperature sensor failure but my experience says it is possible. Or the connector is bad. Unfortunately local dealer diagnostics are not good. Last time they told me that my problem is with intenal air probe (#5 on above scheme, near the lamp). I had 2 additional sensors and tried without success.

[486]

PS: Is there method to deactivate automation of A/C? AFAIK, when temperature is 30°C, it is always heating (100% heat/0% cold). I want temporarily to deactivate A/C while searching for sensor replacement and avoid frequent position changes of valves.

[486]

I found another sensor (OEM code 6445.S4). ServiceBox says it exists on my 406 but cannot access the scheme with location.

[frog]

Here it is:

6445 S4.png

[486]

Thanks. It seems "Search" button in ServiceBox finds all options for a detail. I supposed that it filters only for my VIN.

[486]

Old topic, still actual for me. Is there a scheme for paths of cables? I want to know the cable for temp sensor near lamp.

[486]

I am nearly sure what is the problem in this old case. It is sensor #2 (6445.JA). Now the question is now to access it. It is partially visible when CD audio is removed but it is too low. Is there a way to catch it without complex dismount?

[GingerMagic]

I've removed this sensor once before but I can't remember for the life of me how I did it.
I'll have a butchers tomorrow morning and refresh my memory then I'll let you know