VW MK5 A/C not switching on

[Callum229]

Hi guys.

So I have fully "rebuilt" my AC system. 2007 Jetta 5 TDI DSG.

New pipes, new lines, new solenoid for the AC compressor, compressor inside was spotless, not a speck of dirt.

Problem came when I wanted to regas it. The guy pressurised the system to about 2.8 bar as I can see it on VCDS. It's holding pressure as well. He said he couldn't fill the system due to the compressor not coming on.

However the compressor on VCDS shows code

12 = Compressor OFF: Shut-Off requested by Engine Control.

Compressor is fine(physically checked shaft and shear plate), solenoid is fine(used VCDS to send current signal to it), pressure is high enough. Why would the ECU stop the AC from coming on.

I have been looking for hours through forums what this code would mean, to no avail. No one can seem to point out what this means and what would cause it.

As it would seem like everything is fine, there isn't any codes for the HVAC system, on the engine side, just EGR flow too low and MAF.

HELP.

And thanks in advance.







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[Howie-WP]

solenoid is fine(used VCDS to send current signal to it), pressure is high enough.

I can't help with your issue (but have issues with my aircon too) Where in VCDS do you check the above?

Also compressor kicks in when the pressure valve sends a message to it, you've checked those as well? What is the pressure value for it to activate, maybe too low or too high?

[Callum229]

Hi Howie

These can be seen in measuring blocks under Auto HVAC.

There will be a label there, compressor shut off code. Just put mouse above it to let you know what caused the compressor to not work.





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[Howie-WP]

These can be seen in measuring blocks under Auto HVAC.

Cool, managed to find that, mine is on at least Thanks for the tip on the mouse over wrt codes Where did you power test the solenoid via VCDS? I did mine manually and can hear it activate.

Your case with the ECM shut off is odd? Nothing on ross tech forums?

[Callum229]

If you go down to output tests and select begin, it should start testing the whole AC system, towards the end, it will test current to the compressor solenoid. If you have the solenoid out, you should be able to see it move and pulsate open or close.

For some reason I had to have the car off in order to test it. It might not be necessary for you though.

What's the issue with your AC? As I read so much things, I might be able to help.

And no, no one seems to know the solution to the error code 12. I seem to have an issue that one or two people had.....

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[Howie-WP]

If you go down to output tests and select begin, it should start testing the whole AC system, towards the end, it will test current to the compressor solenoid. If you have the solenoid out, you should be able to see it move and pulsate open or close.

I just found the output tst section while trying to diagnose an issue on my Treg. I am a noob with VCDS despite having the cable for ages I check my solenoid in situ while powering up the unit and heard it pulse.

What's the issue with your AC? As I read so much things, I might be able to help.

Not sure and don't trust the x2 people I took it to thus far. One was adamant the solenoid was GF.A'd and the other wants to replace the entire aircon system. It is not getting cold and I suspect a leak somewhere. I got them to include some dye so will check and see. I want to make sure the system pressurises correctly and then take it from there......

And no, no one seems to know the solution to the error code 12. I seem to have an issue that one or two people had.....

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Odd one that, it's like the ECM is not seeing it or it as error'd somehow? Wiring maybe?

[Callum229]

Ah.

Don't stress, I am also a noob, you only become an "expert" if you can't solve your problem and look for every possible avenue for issues.

I have an AC guy, thankfully he is the best in the business. He spent about 2 hours yesterday trying to diagnose the car from checking plugs, codes, ambient sensor and compressor. I have been using him for all my vehicles, he has a small shop and refuses to charge me unless he finds an issue. He told me to leave my car there and he will spend a day trying to diagnose it. Sometimes it is the small shops that would go the extra mile and not charge you and the big ones that just randomly throw parts at your car trying to fix it. Granted my issue is something with wiring or ECU so I will check all of that first.

Expansion valve probably for you? If the system equalizes in pressure(high and low side), then your expansion valve should be fine. Also check that your compressor shaft is spinning with the wheel(centre nut must be spinning when engine is running) if not, then your compressor has jammed and sheared off the shear plate. If you gas up and pressure is fine, the AC should work regardless of a slow leak, as long as there is pressure reading on VCDS showing above 2.8 bar.

No the ECM is seeing it but not allowing it to trigger on. I have cleared all codes on the engine side and enabled EGR as well as MAF. Still nothing and the engine keeps preventing the compressor from coming on. I think it might be a wiring issue but not sure how as there is no code saying anything is disconnected or shorted out. Very mysterious, and it is just like me to have an issue that no one else has....

[Howie-WP]

I think it might be a wiring issue but not sure how as there is no code saying anything is disconnected or shorted out. Very mysterious, and it is just like me to have an issue that no one else has....

Is there no way to hard switch it on (by passing the ECU)?

[Black Widow]

Start with checking your pressure switch. If it is faulty your A/C wont get the correct reading. It will be either to low of high thus not coming on to protect your AC system.

[Callum229]

Have checked and changed pressure switch, still the same issue. I can trigger the AC manually, but the car won't allow me to trigger the AC. Suspect something is wrong with my cluster though so when I swop it out I will update you guys.

[hidibarni]

Hi ,

What was the problem ?

I have this problem too