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 Post subject: S2 Heater problems
PostPosted: Mon Dec 18, 2017 10:31 pm 
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Last winter our central heating boiler decided to die on the coldest day, this year it's the 944. On the way to work no heat at all. Searched t'int and cleaned, tested interior temp sensor, checked external temp sensor reading ok. Now on defrost the actuator arm moves and I get heat, set temp at 24 fan at 2 no heat. Temp at max heat for a while then cold, I can watch the actuator close. There is another sensor but I've no idea where it is and if it is causing the problem or is it an internal CCU fault? To add to that my button on the slider broke. Have you seen the price of them!

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Dec 19, 2017 10:58 am 
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there is a thermistor in the mixer chamber of the airbox

think there is a repair kit for it,

Temperature sensor repair kit without connector housing, PCG 653 121 00 £83.33 +VAT = £100

there is a sensor in the air intake of the interior fan, a thermistor, also one in the air flow of the right hand intake by the wiper motor,

I do believe they are all the same thermistor, ND03N00103J, RS part number 967-4465,

I have ten of the little things

the slider knob is 944 653 205 00 01C @ £28.06 each

mine played up and I discovered it needed the RH plug and pins cleaned on the back of it

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Dec 19, 2017 2:49 pm 
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That's great info thx. Bit of a price difference between the kit and a single thermister :)
I also found this https://www.sterlingsensors.co.uk/ntc-t ... gLpe_D_BwE which may do the trick if the one in the mixer chamger is caput.

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Dec 19, 2017 3:22 pm 
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might do the trick, I just don't think its going to be much fun to change at all

think I got ten solder in ones for £3

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Dec 19, 2017 3:42 pm 
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Just checked the one behind the vents and it's reading very low around 1.5Kohms. It looks a lot easier to change the thermister than the full sensor plus lead. How the hell do you get at that plug?

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Dec 19, 2017 7:38 pm 
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that's what I thought, time to get the soldering iron out

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 Post subject: Re: S2 Heater problems
PostPosted: Thu Dec 21, 2017 11:06 pm 
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Changed the thermister (many thanks Waylander), still no joy. Took the mixer flap motor off to check, working fine. Heater valve works but only on defrost. All sensors check out. It's as though the temperature controller circuit has a fault. Next thing to check is the solenoid for the heater valve but if defrost opens it I doubt it will be the problem. Just found a cheap CCU, just hope that works.

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 Post subject: Re: S2 Heater problems
PostPosted: Thu Dec 21, 2017 11:23 pm 
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It will be the right hand knob/switch in the heater control unit, I have a few of those

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 Post subject: Re: S2 Heater problems
PostPosted: Wed Jan 17, 2018 2:40 pm 
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Fitted a replacement ccu (supposedly working) no change. Took solenoids off checked both working, one wire broke at the socket so strip, resolder and refit. Access is really difficult, had to remove steering wheel and intrument binacle. Amazingly the ABS self test worked for the first time in 6 yrs, can't understand how the abs and ccu are related unless I re-established a bad earth somewhere.
I've disconnected the vac line to the heater valve so hopefully I will get constant heat now without having to put the defrost on though I may have to fiddle with the mixer flap as well.
Do you ever feel like srceaming in a confined space?

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 Post subject: Re: S2 Heater problems
PostPosted: Fri Jan 19, 2018 1:52 pm 
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Set the mixer flap to full heat and heater valve fully open. I pulled the vac line to the valve and sealed it them unplugged the flap motor. Now I've got constant heat and can still adjust fan speed, will do for now. I checked the voltage on pins 4 and 5 of the mixer flap motor and it's steady at 10v not responding to temp controller. Potentiometer works so it must be the IC4 chip. There are 4 ICs on the PCB all the same so I'm going to cannibalise the obviously duff and very cheap ccu I bought and swap the IC4 on my original ccu. If this works there is a potential saving of several hundred pounds. Crazy when a component goes pop costing a few pence and you can only buy a full unit for several hundred. The good old days with carbs , points etc.
Partner's Mito electric power steering died, luckily you can get a £150 exchange unit, over a grand from Alfa. The only place I have found to test and repair 944 ccus is in the States but I have a contact that repaired my 993 OBC so I'll see if he can sort it.

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 Post subject: Re: S2 Heater problems
PostPosted: Mon Jan 22, 2018 10:05 pm 
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I have the exact issue but the opposite, mines constantly sending heat to the interior! Have replaced the IC4 but no success. Can always see the heater valve open once car has started.

Car is now at body shop so will have to tackle this challenge later on.

Will follow this topic...


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 Post subject: Re: S2 Heater problems
PostPosted: Tue Jan 23, 2018 1:59 pm 
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Heater valve opens and closes with vac supply controlled by the 2 solenoids on the right hand side of the heater box, could be the one that controls the vac supply to heater valve or a vac leak. I replaced mine but no joy.
Vac closes the valve, no vac opens.
I've taken the plunge and bought a new ccu (that did smart) not fitted it yet. The cost from the place in the States that rebuild them wasn't much different to new. I shall cry if it still does not work.

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Jan 23, 2018 4:43 pm 
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Hi Endoman,

Before you spend a tonne of money on the CCU have you thought about buying new IC4s and changing those over (you did mention it earlier in the thread but I didn't see any mention of the result)? I did a search and a guy on Rennlist appeared to have a similar problem to you and fixed it by soldering in a new IC4. It looks like a simple op amp so with a few anti static precautions during the soldering it should be a simple DIY job. From what I read the generic part code is LM2902N (you'd need to check this) which appear to be readily available in the UK.

I share your hatred for having to replace expensive items for the sake of a couple of pence component.

Good luck with it.

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 Post subject: Re: S2 Heater problems
PostPosted: Tue Jan 23, 2018 9:40 pm 
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The guy on Rennlist was dealing with an earlier CCU, same schematics but different components. The ICs on my board are all Siemens 4201S1. I'll have to give it to someone who has the experience and skill to do this but I will persevere.

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 Post subject: Re: S2 Heater problems
PostPosted: Wed Jan 24, 2018 11:57 am 
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Hi Endoman,

I had a look at the Siemens chip you mentioned. It appears to be a single inline package with 9 pins (i.e. 9 pins only on one side of the chip). Is that correct with what you can see on the board? I notice that the other item I mentioned from the Rennlist post is a dual inline package which has pins on both sides of the part. It seems that the Siemens item is no available (although some companies claim to have stock) even under the Infineon brand (which Siemens Semiconductors became some years ago) but the dual inline package from the earlier board is available.

Obsolescence in semiconductors is a major hurdle to keeping these boards up and running.

It sounds like you are on the case anyway so hopefully you will find a solution.

Matt

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