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Discussion Starter #1
Hi, been struggling with my AC system and with the summer heat I’m eager to fix it. Over the past year the problems gotten worse and worse. My AC system will just randomly restart itself and revert its settings back to whatever they were when the car first started up.

AC still blows cold and the heater still works. It’s always been a bit slow to heat but I rarely need to use it.

I’ve replaced the blower motor resistor and that changed nothing. It doesn’t seem that my refrigerant is low as I still get cold air relatively quick.

Any ideas for where to look next? I understand that there is a pressure sensor on the dryer but I’d prefer to avoid needing to recharge the system unless necessary.

2003 330ci 5 speed. It’s a preLCI and is fully optioned.


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The Final Stage Resistor on these cars is notorious for causing issues like this. Probably time to replace it if you don't know the age of it. Not a hard DIY but it can be an ergonomic challenge, especially if you're a big fat dude.
 

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The Final Stage Resistor on these cars is notorious for causing issues like this. Probably time to replace it if you don't know the age of it. Not a hard DIY but it can be an ergonomic challenge, especially if you're a big fat dude.
Blower motor resister == final stage resistor

Same thing, different names. I replaced it and it was in fact the original resistor. Problem still persists. Anyone know of a way to test it? Don’t really want to deal with a return and replace if it’s not bad.


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Step one is scan the IHKA for trouble codes. That’s the best clues you’ll get.
Will do. I have a capable scanner. I can also test the module. Is there anything there worth testing?


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If you have BMW Standard Tools, run INPA and see if there are any tests on the IHKA page.
If you don’t have that set up, hit the BMW Standard Tools link below for details.
Don’t have INPA or any of that setup. Scanner is a Foxwell NT510 with the BMW specific software. I can see, check, and test all the modules.

Anyways, checked through the IHKA module and there are no codes. I checked the live data and found something interesting, though.

Car is saying the interior temp is 90°. The exterior temp is 87° but the car feels closer to mid 70s. Maybe the high reading is why my auto setting is useless.

The “Pressure sensor (system pressure)” is reading between 14 and 15 bar. That seems excessively high. I’ve never topped off the refrigerant so don’t blame me.

I guess that’s my first step, then. Any other ideas?


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I would have thought final stage register as well. But I believe you are onto something if the interior temp is reading 90 but the exterior temp is 87 and you feel like the interior temp is in the 70s. Unfortunately, I don't know too much about the interior temperature sensor. But I came across the following using Google which may be helpful:


Perhaps you can use some compressed air as the above suggests. I wish you luck.
 

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Mine has occasional bouts of amnesia as well. DO clean your sensor and make sure the fan still works
(it's a dinky little computer- type fan, and they do fail. The bearings wear out)
You have to open the IHKA itself to check the fan.

But I suspect, since I have caught mine doing it, that something is either interrupting power
OR causing a hard reboot of the unit, because the display blanks momentarily, then
resets as if the car was just switched on. Nothing else does, so it's not a main or unloader relay.

t
hasn't fixed his, either.
 

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Blower motor resister == final stage resistor. I replaced it and it was in fact the original resistor.
Probably not the FSR then if you replaced it with a good quality OEM part and not some cheap Asian crap.
 

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Probably not the FSR then if you replaced it with a good quality OEM part and not some cheap Asian crap.
about that... probably going to buy a known high quality FSR as I may have gotten a cheaper one thinking they’re all the same...

Symptom wise it didn’t seem like a FSR issue but I know the OEM part will fail so I just replaced it first.


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