christallon

Hi all. There is a humming sound coming from the passenger side, under dash area of my 93. It may be the locking control unit. I have done a search and have not found anything definitive. When I disconnect the battery ground the noise continues for a few minutes until it dies off. It's almost like it takes and stores a charge there. I just recharged the battery to see if the weak battery was the culprit, but when I reconnected the charged battery, the sound starts up again. This is with the key out, motor off and sitting still in the garage. Does it sound like a bad control unit, maybe? I have not been able to hunt down the noise specifically, but it is certainly coming from the passenger side under dash area. Any other thoughts?

The central locking system works as it should, and the key locks and unlocks properly from the doors, and enables the alarm as the red lights start to flash in the door lock. I can't unlock the doors from the inside using the console swithch though, I need to manually turn the door unlocking wheel to unlock. Is the console switch supposed to unlock the doors as well, or is this purely a manual operation?

Many thanks in advance.

Tmistry

Mine does this too. I thought it was normal. Like oil drips and the sweet smell of a hot engine.

mdsarch

+ 1
Mine does this as well, stops after a few minutes.

christallon

Mine never stops making the humming noise. Any other thoughts? I believe it also draws down the battery. TIA gang

christallon

So I found the culprit. I took the passenger seat out so I could get under the dash and snoop around. I found that there is a tiny fan that runs behind the climate control unit, left side closet to the driver side (LHD). Its a tiny fan that runs all the time. I'm sure it's supposed to shut off when the ignition is shut off, but in my case it always runs. I wonder if its there to mix the air so it can be sent into the temp sensor. Any ideas how to rectify this? The climate control unit functions as it should, so there is no problem with that. It's simply that darn tiny fan running, and I'm sure it pulls juice from the battery too. Thoughts?

tcnicholas 964

http://www.porschehvac.bergvill.com/

You will find your answer here.
Tom

christallon

Thanks, very interesting stuff here. Cheers!

boxsey911

Mine was running all the time and causing a drain. It wasn't so much hearing the little it fan, it was because I could hear the relay in the CCU clicking. Even though the car had not been run for days. So I followed Tore's guide in the link given by Tom above and replaced the BC337 transistor that controls the relay for the little fan. The fan now goes off as it should and the battery drain is gone. Total cost about $0.50 and my time.

christallon

Thanks Steve. Was it a difficult time consuming job to replace that transistor? I read through the instructions quickly last night. It appears I don't have to separate the boards. Was it simply a soldering gun job?

Many Thanks. How are you BTW?

boxsey911

I'm good thanks Chris.

No need to separate the boards. Locate the transistor next to the relay and take note of which way the flat side faces relative to it (I wrote it down but can't find the pieces of paper!). De-solder it the other side with the help of solder sucker and then use tweezers in the gap to wiggle it out. The key to getting the new one in the board holes is; separating the legs, bending them and tweezers. Here's mine soldered in place before I snipped the legs off:



I probably spent more time taking the CCU apart and even more time being careful to put it back correctly in the case - Tore mentions this is the bit that can cause damage to the boards if they're not put correctly into their guide slots. When taking apart there's no need to remove ***** or sliders but there's a pin connector behind the face that you need to remember to replug when reassembling.

christallon

Great, Thanks Steve. Perfect instructions.

JasonAndreas

I have some additional photos HERE which show the location of the other component removed.