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Replacing the Evaporator Temperature Sensor

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Old Oct 21st, 2020, 07:56   #21
theseriojca
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Hello,

Still not had a chance, unfortunately, no real need for aircon till summer now, so will leave it till a nice sunny when I got nothing else to do (wishful thinking!)
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Old Jun 1st, 2021, 22:15   #22
theseriojca
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Default Reviving the thread

So, got some time to fiddle with it, but still no luck.

Unplugged the green connection at the back of the CCM, which in my case looks like this.



No corrosion or signs of short circuits.

I've cut the purple and brown wire and connected the sensor to it - no change.

The sensor's resistance is about 2.8kOhm, which corresponds with the table. The resistance in the brown and violet cables (with the green socket plugged in) is about 14kOhm. There's current flowing through the 2 wires when plugged in as well.

No matter whether the sensor is connected or not, the reading in VIDA says 100 degrees C.

What else can I try? A different sensor?
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Old Jun 3rd, 2021, 13:37   #23
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As a final check I'd connect a standard 0.25w resistor of either 4.7k or 5.6k in place of the sensor. Then if the fault code for the sensor comes back after clearing it, and VIDA still reads 100 degrees C (or some other, clearly erroneous value), then you should conclude that the CCM itself has an internal fault and requires either replacement or board level repair.

Given what you've done so far, and that the replacement sensor's measured resistance is within the expected range, I'm inclined already to suspect CCM failure.
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Old Jun 4th, 2021, 14:10   #24
theseriojca
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Thanks, Moose, will give the resistor a try.

Can anyone advise on which CCM I would need? As in, do all of them come with the same 'back', but I would need to add the front buttons from my existing one? I've only got one empty button slot, but most CCMs I've seen for sale have lots more.
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Old Jun 14th, 2021, 23:19   #25
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Default Right on the money!

Quote:
Originally Posted by Moose Test View Post
... I'm inclined already to suspect CCM failure.
What a God send you are, Moose!

I should've 'joined the dots' myself earlier, but I was trusting VIDA too blindly! After your reply, I went onto eBay and found a used CCM for an amazing £17, posted. Thought 'what the hell', I'll give it a try.

Here it is, in various stages of disassembly (just in case anyone needs to see one taken apart).













I have removed the existing CCM:

Pull up on the gear stick stick surround, with the cupholder slightly open and then unclip the silver surround as well.



Undo the bottom two T25 screws and remove the CCM and the Entertainment unit.



This is the cavern left after disconnecting all the wires.



Here are some pics of the two modules connected, note the 4 T25 screws and the 4 clips that need undone in order to separate the two.







Here's a picture of the existing circuit board, could not fault it just by the look of it.





The swap of the circuit boards was pretty straightforward - word of advice, make sure all four temperature knobs are turned the same way - straight up, for example, otherwise the board would not fit properly and you risk damaging it.

Put everything back together in reverse order, hooked up the new evaporator temperature sensor and hey presto! all working perfectly!

Gave it another thought and decided to re-attach the existing temperature sensor, the one I cut off a while ago - works a treat! So it was never the sensor itself, it was always the board that went bad.

Put everything back together, cleared all codes and got the all clear!



Big thanks to everyone who replied and guided me on this journey, especially Moose Test! It's about 12 degrees here so not sure if the aircon will need recharging or anything, will need to wait for a warm day now. 'Mon the heat!
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Old Jun 15th, 2021, 23:45   #26
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I'm glad that you got it resolved and at a reasonable cost. I think your experience here yields two important take home points for others.

Firstly, how invaluable having a copy of VIDA and the wiring diagram are to a methodical, well reasoned diagnosis.

Secondly, whilst the fault detection and reporting capabilities of the car's control modules are very good (particularly for the period of their execution), they were designed to a price point and thus are not fully exhaustive nor with it infallible. In this case, the CCM's internal error checking routines were able to pick up that the measured temperature value was outside of the expected plausible range but weren't comprehensive enough to be able to really determine the root cause. i.e. distinguish a failure of the sensing element from that of the sensing circuitry itself. All it could do was raise the generic "sensor warning light" and let you do the rest. Or to put it another way, DTCs don't really lie as such but it's often important to understand their context in terms of the way in which the associated systems work and their relationship with others.
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Old Nov 6th, 2021, 22:30   #27
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HI Theseriojca,

Did the code numbers on the replacement CCU match the numbers on the back of your existing one ? I"m sure you are aware that certain units cannot be interchanged because of programming issues.

Jude
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Old Nov 7th, 2021, 08:30   #28
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Quote:
Originally Posted by jnmonaghan View Post
HI Theseriojca,

Did the code numbers on the replacement CCU match the numbers on the back of your existing one ? I"m sure you are aware that certain units cannot be interchanged because of programming issues.

Jude
Hi Jude,

No, they didn't. I just took a gamble, the donor part was from a 2010 car as well and it just worked out.
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Old Dec 14th, 2021, 21:52   #29
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Default Mod. to the Evaporator Casing

A tip for making a perfect hole in the casing - to take the replacement sensor - after starting it with a soldering iron,- Use a CONICAL wood/plastic cutter with a hex. shank.

Jude
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