Fabia evap temp sensor - how to (with pics)

[ap0gee]

Another fault that's appeared on Mrs. Ap0gee's new car is that the air con only works when you first start the car. Switch off the ignition, and it won't work again until the engine's gone cold. This is a sign that the evaporator temperature sensor's gone, and it's something that's been covered on here quite often. The following how to's based on stuff already posted by Lummox and VRStu (and a recent 'helpful hint' from Bigw2069). I just followed their lead and remembered to have my camera with me when I did the job!

NB: There is now a printer-friendly pdf version attached at the end of this post!

You will need a small screwdriver or trim removal tool, and a 3mm (I think) Torx screwdriver. The part number is 6Q0907543D, and I paid GBP15.02 incl. VAT.

1. Remove the headlight switch, by starting at 0, pushing it in, and turning it to sidelights. It allegedly pulls out, but I needed to give it a hand with my screwdriver (use a trim removal tool if you've got one!) Once it's out, remove the switch unit from the wiring.

2. Pull the right side of the bit of trim above the steering wheel towards you (1), and then push it up a bit to allow you access to remove the Torx screw underneath (2):

3. Now lever off the fusebox cover:

4. ...and remove the screw shown:

5. Now remove the three screws shown:

6. ...and this one, too:

7. The dash panel will drop down, and you should remove the OBDII socket from its holder (undo the three clips with a small screwdriver, and push the socket through from the other side):

8. Remove the screw shown, and pull off the footwell air duct:

9. Disconnect the clutch switch (1), turn it 90 degrees to the left (2), and pull it out of its holder (3):

10. Remove the central locking ECU and its bracket. It's really tricky, so I ended up just ripping it off and busting the bracket in the process! This is easily done, apparently, and you can always just use a cable tie to hold it in place once you're done - no-one will ever know! ):

11. The sensor is up at the top somewhere. It's only held in by friction, but you will need to disconnect it from its cable, which I found quite tricky. If you get too frustrated, you could always leave it connected and snap the sensor to get it free - you're replacing it after all, and it should be easier to disconnect once it's hanging down where you can see it! The picture for Step 12 kind of shows you what you're feeling for (only the bit to the right of my thumb protrudes from the bowels of the car...)

12. One knackered evap temp sensor. I'm glad I took this photo, as I put it down next to the new one, and couldn't tell which was which! Fortunately, the old one had a blue wire running down the middle, completely surrounded by plastic, whereas the new one I got had a black wire held in a sort of groove:

13. Reassemble your dash, following the above steps in reverse order. You'll probably have a bit of trouble with the rubber tube for the can cooler, but I removed it from the top of the can cooler, and inserted the other end into the hole in the bottom of the right-hand dash vent (circled), which made it easier...

Reassembly might take a bit of "percussive adjustment", but it's fairly easy! It doesn't seem to matter if you can't reset the fault codes yourself - the air con will be back to normal regardless (if that was what was wrong!) As I said in another how-to I've just posted, though, warn your garage before THEY read the fault codes, otherwise they might do the job again and charge you!

HTH

[devonutopia]

This isn't the "high pressure sensor" is it? Great guide though.

[VRStu]

Great guide - Well done.

One point I'd like to make as the remover of many a Fabia knee panel I Find it easier to remove the aircon pipe from the top of the storage tray rather than the vent pipework. When replacing open the stoarge tray and support the slider whilst pushing on the hose.

[Lummox]

Moved to the technical guides section.

[mygokhan]

very very thanx! good guide

[echase]

Good guide but I found that it is possible to quickly remove the ECU with minimal/no breakage. The ECU slides into a plastic frame/bracket; leave it in its frame. This frame has two V shaped lugs on it that slide into 2 slots in the car metal chassis. If you slide a medium sized flat screwdriver up and forwards between the frame and the chassis exactly in the middle, between the 2 lugs, which you can't yet see, it should release the plastic catch the locks the lugs into the slots. Then the frame can be slid up and backwards (or is it down and forwards?) 5mm to free it. If that does not work (probably because you missed the locking catch) just force the screwdriver in hard till the plastic lugs break.

Although I did marginally break one lug I found I could slide the frame back into the slots and it locked solidly enough.

Any chance someone could photograph these lugs and put photo here?

Took me 45mins but I had previously changed my brake switch so knew how to do half the steps.

Beats me how Skoda is so incompetent as to sell a sensor that is so unreliable. At its heart it just has a small Themistor, the little bead at the end. These can be bought for a few pence and are so simple they should never fail, as long as the wiring is waterproofed with varnish or similar. I suspect Skoda has not waterproofed them so the damp air corrodes the wires. I am a Reliability Engineer.

[vstoyanov12]

Hi apOgee,
I followed your very good guide as I have also the problem with the ev. sensor on my Fabia 1.4 which I bought new in 2002.-This year I found that a/c is not OK.When I first start the engine -a/c works but soon it will stop and blows no cold air .After a stop and cool out of engine it may start working again for a while.
Some days ago I went to the SKODA service in Sofia(I live in Sofia-Bulgaria).I was told by an technician that my compressor is foulty(cost about 500 Euro-two month's average salary). Luckily I have red your posting here and I decided to replace the ev.sensor myself(I bought it for 15 Eu.)So I refused to replace the compressor-instead I decided to replace the sensor and do it myself-to save another 50 Euro or so.
I followed your picture instruction which I printed from the pdf file,step by step-and it was ok(I would never disassembled the dash without your guide).Disassembly lasted about 1/2 hr. but than when I started trying to remove the sensor from its hole(to pull out the plugged in the sensor 2 wires switch (connector) with one hand only I couldnt. But I did not give up and went on trying-about 5 hrs. but with no result. Eventually I cot the 2 wires ,took easily the sensor out and adding new pieces of wire to prolong the existing ones I connected the new sensor with the switch and thrusted it into the evaporator's hole.The reverse assembly lasted abt. 1 hr. and again your guide was very helpful.So after 7 hrs. I fixed the new ev.sensor and the a/c started to work normally.Well my spinn ,backhead ,ribs ,neck and and hands were to painful for one day or two from all the overhead job done with my body almost hanging upside down from the seat under the steering wheel and looking up in a small dark hole with a hot lamp near my head to see the bloody sensor (never in my life have I tortured myself so much doing a mechanical repair).Anyway I am now satisfied asl my aircon is working well and I will survive from the hot weather driving withmy Fabia.
Thank you again.

[ap0gee]

^^ I know what you mean about the sensor being hard to remove - what price a few extra centimetres of wire, eh?! I'm glad your A/C is up and running happily again, even if it took so long! I'm sure you'll be able to buy a few beers to help you relax with all the Euros you saved by doing the job yourself! But I can't take all the credit - Ross and Stu did all the hard work; I just followed their instructions and took the photos! Glad to be of help all the same!

[Lummox]

Also works on the 9N Polo as I found out last week

[maherto]

I have a fabia were the air con does not work, if i put 12 V on the compressor clutch the pipes get cold and i have cool air. If i measure the voltage at the plug on the compressor when the air con is on or off i get 11.5 volts but it does not have the current to light a 5w bulb any ideas or does any one have a wiring drawing instead of ripping looms apart.

[vstoyanov12]

Thanks apOgee! I will trink couple of beers for your health too. Better if I could treat you with good beer ).

[ap0gee]

Originally Posted by maherto

I have a fabia were the air con does not work, if i put 12 V on the compressor clutch the pipes get cold and i have cool air. If i measure the voltage at the plug on the compressor when the air con is on or off i get 11.5 volts but it does not have the current to light a 5w bulb any ideas or does any one have a wiring drawing instead of ripping looms apart.

I'm no expert, but the A/C is mostly a mechanical system, not an electrical one. The wiring is all to do with controlling rather than operating the system, so I can't imagine the currents involved are particularly high (hence the lamp not lighting). The evap temp sensor is part of the control system (obviously), and so if it's failed the entire A/C system won't work. Actually, that's not entirely true. In my experience, a fault with the evap temp sensor can mean that the A/C works for the first minute or so after you start the car from cold, but doesn't continue supplying cold air once everything's warmed up. It may be work seeing if that happens.

Another control system possibility is that the external temperature sensor may be faulty, as the A/C is disabled below 4degC. See if the temperature readout on the dash is correct, as this should also be affected by the same fault.

The fact that you can fool the A/C into working suggests it's a control system fault rather than a knackered compressor or lack of refrigerant, so I'd recommend checking out the sensors mentioned above. I'd be surprised if any of the wiring had gone, as it's all within the dash or under the bonnet, so there shouldn't be too much of a problem with the insulation or the wire itself breaking like can happen with wires running to the doors and boot. Unless water's got in somewhere, of course! If anyone else on here has any suggestions, I'm sure they'd be gratefully received!

[Bigw2069]

good guide, got the CL ECU bracket eventually, by pushing it towards the steering wheel. couldnt get the clip off the sensor with one hand and i'm too big of a laddie to get 2 hands in, so pulled the sensor out as far as it would go with the cable attached and snapped it, easy to remove after that!

[echase]

Dear Maherto. I also tried the add voltage trick and it all worked but I was advised by someone on this site (search for 5 volt, 12 volt and echase) that it’s meant to run at 5V max and that 12V may damage it. It does not light a bulb because it’s just signal level current. And/or it will not be switched on if you have a sensor fault.

Note that you are bypassing some of the safety sensors like overpressure switch by doing this so beware and only run it for short periods. I used cigarette lighter mobile phone charger to get the 5V. I changed the temp sensor later and all is well, see my post above.

I never quite got to the bottom of whether it’s 5V for on and 0V for off, or a graded 0-5V signal giving variable output for the compressor based on swash plate position. Also does anyone know whether, if you set the temperature control to midway, does it mix hot air with cold or does it alter the swash plate to get less cooling, with less hp into compressor, thus saving energy?

[ap0gee]

AFAIK, the air con works by cooling the air to the maximum (i.e. the temperature it would come out at when set to 'blue'. I think this is about 16degC, so the wobble plate still varies the amount of compression required because it'll take more to cool 40degC air to 16degC than it would to cool 20degC air to 16degC. Then the cold air passes through the heater matrix to heat it back up to (roughly) the temperature shown on the dial.

There are two reasons for this: Firstly, the air con does not just cool the air, it also dehumidifies it, and if you've ever been somewhere like SE Asia or Central America, you'll know that humid is as bad as hot! Second, the hot air from the heater matrix is essentially free as it comes from the engine via the coolant circuit. Therefore, you're not really losing anything by heating the pre-cooled air up again. In fact, I gather it can benefit the cooling of the engine, as I remember being stuck in a traffic jam on the M5 many years ago in an overheating Metro courtesy car, and my dad opened all the windows and turned the heating up to full, and sure enough the engine temperature dropped!

[echase]

Thanks for explanation. I used to live in SE Asia and cars there have similar systems but the compressor is bigger and you sure notice the engine slow down when the compressor engages.

[maherto]

Hello Echase,
with regard to the 0-5v thing, it should be a 12 v supply to the compressor clutch plate to turn the air con on which engages the clutch and allows the belt to turn the vanes in the compressor. Their aint much anloge singnals involed as the compressor clutch is either on or off now air con in your home or the like will have some form of anloge system which will vary the displacment of the vanes or use a VSD drive to vary the speed of the motor driving the vanes. what i would like to know is where the 12 v is switched from as i dont realy want to cut in the wiring loom to trace the cable, its only my wifes car and this is the only problem with it apart from a rattling timing chain but i will worrie if it stops rattling!!!

[maherto]

Oh dont mind my speling working shift nighs?

[ap0gee]

Originally Posted by maherto

Hello Echase,
with regard to the 0-5v thing, it should be a 12 v supply to the compressor clutch plate to turn the air con on which engages the clutch and allows the belt to turn the vanes in the compressor. Their aint much anloge singnals involed as the compressor clutch is either on or off now air con in your home or the like will have some form of anloge system which will vary the displacment of the vanes or use a VSD drive to vary the speed of the motor driving the vanes. what i would like to know is where the 12 v is switched from as i dont realy want to cut in the wiring loom to trace the cable, its only my wifes car and this is the only problem with it apart from a rattling timing chain but i will worrie if it stops rattling!!!

Just to let you know, there isn't a clutch on the Fabia A/C compressor - it works on the wobble plate principle, and so is always rotating as long as the engine is turning. The only thing that varies is the level of compression. Even when the system is switched off on the dash, there is still a small flow of refrigerant going through the system, which helps keep the seals etc. in good condition.

I believe the only time there's no flow at all is when the exterior temperature sensor reads below 4degC, and this is to prevent the evaporator and low-pressure lines freezing on the outside in cold conditions.

Hope this helps...