AC working intermittently

[MihaiBogdan93]

Hello all,

I have an Audi A4 B8 2009 1.8 TFSI with a more particular issue. The story is like this:

I bought the car in June 2019 and i recharged the AC (i don't know with how much refrigerant because i wasn't present). It worked fine for 1-2 months.
Somewhere in August it started working intermittently (like 70% of the time was working and 30% not) when the AC was on. In a matter of 2-3 weeks, it went on working only (20% of the time i needed it and 80% was not giving cold air). Because of the heat wave from back then, i went to a new garage and recharged again with refrigerant (also to see if there are any major leaks in the system). They added extra 80g of refrigerant in order to top it up to 540 g. It might sound a lot, but as i specified before, i don't know with how much they recharged it first time in June.

The AC worked again 100% for about a week, after that it started again to work intermittently. Decreasing in the amount of time working as the time passed. But when it was working, it was giving cold air as a normal AC.

Since October 2019 until July 2020 i didn't had time to check the AC of the car.

Now the more in depth story comes.

In July i took the car to another garage to refil the system with refrigerant and fluour in order to check for leaks with UV lamp. Didn't performed the UV check yet. They added 100g of refrigerant to bring it back to 540g. They checked for errors and said that the AC is not working because of the Auxiliary Heating system of the car (HVAC) due to the following error:

01207 - Control Module for Auxiliary Heater (J364)
004 - No Signal/Communication

At that moment i believed the garage guys and started to investigate into this. While checking fuses, connectors, cabling and the unit itself i determined that this could not be the culprit of my AC working only 10% of the time. Since i bought the car the HVAC system didn't worked at all and it had this error, but the AC worked perfectly.

I changed my investigation into AC system again and determined the following:
1. The AC pressure sensor is working
2. The AC compressor rubber clutch was checked and is ok
3. The AC is giving cold air randomly, usually when the engine is idling. When in load (aka driving) it rarely works.
4. I connected an override tool to the AC and it didn't deliver cold air.
5. Measured the wires which are going to the solenoid valve on the AC and they receive signal (11-12V). I don't have a osciloscope to measure the duty cycle.

Considering the AC works from time to time, i don't really believe is the AC compressor, but the solenoid valve.

Any ideas, opinions or experiences with a similar issue ?

[Chillaxin]

If you've had to refill the refrigerant 2x, you have a leak somewhere. If the refrigerant level completely leaked out and sat unpressurized for a length of time, you'll likely need to replace the drier or desiccant pouch (whichever your car has) after you find and fix the leak. Have the shop pull a vacuum on the system for > 2hrs before refilling to make sure you don't have moisture in the system. Good luck.

[MihaiBogdan93]

The system was never unpressurized. In both cases, it had normal pressures (according to the garages) and more than 400-450 g of refrigerant. The system might have some small leaks, but this is not the cause of the AC not working correctly.

But thank you for the info.

[SDF1]

3. The AC is giving cold air randomly, usually when the engine is idling. When in load (aka driving) it rarely works.
Interesting. Mine is the opposite, when it is idle it does a little cold air but only when the car is driving then it gives cold air.

I'm thinking it can be 3 items.
1 - Compressor. Not turning on or seized.
Turn the car on with the A/C button OFF. Wait 2-3 min for car to reach temperature and then have someone inside push the AC button and set the temperature to the lowest setting. Have the hood open and listen do you hear the compressor turn on? If it is good. If nothing happens.. try cycling it off wait 30 seconds then back on.

2 - Leak. Slow leak or air/moisture was introduced to the system.
I would recommend you pressurize the system with nitrogen and see if there is a leak. If there is then you need to fix it or try additive that will seal the small holes. Then replace all the old freon with new one that is not contaminated.

3 - Computer not turning it on (Switch, etc)
Check this
https://www.audizine.com/forum/showt...ose-AC-problem
and
https://www.youtube.com/watch?v=Vs_gPccrzu4

[Smac770]

Have you tried logging data to see what's actually going on?
https://www.audizine.com/forum/showt...1#post14214555

01207 - Control Module for Auxiliary Heater (J364)
004 - No Signal/Communication

Why do you have this error? Do you actually have aux heat?
Have you been playing with Carista? Another google hit on the subject mentioned some guy saying "oops, Carista turned that on incorrectly".

[MihaiBogdan93]

3. The AC is giving cold air randomly, usually when the engine is idling. When in load (aka driving) it rarely works.
Interesting. Mine is the opposite, when it is idle it does a little cold air but only when the car is driving then it gives cold air.

I'm thinking it can be 3 items.
1 - Compressor. Not turning on or seized.

I do hear the compressor working when i connect the connector to the solenoid valve. But the fans on the radior do not start to work. When it is blowing cold air, the fans can be heard.

2 - Leak. Slow leak or air/moisture was introduced to the system.

I already have refrigerant with flour in it and can be checked for leaks with UV glasses. Still haven't perfomed the checks, because the garage said to wait 2-3 weeks.

3 - Computer not turning it on (Switch, etc)

i will read through them, thank you

Have you tried logging data to see what's actually going on?
https://www.audizine.com/forum/showt...1#post14214555

I haven't tried to log the data, i will do it next week.

01207 - Control Module for Auxiliary Heater (J364)
004 - No Signal/Communication

Why do you have this error? Do you actually have aux heat?
Have you been playing with Carista? Another google hit on the subject mentioned some guy saying "oops, Carista turned that on incorrectly".

I do have the HVAC unit. I checked the fuses, the cables and connectors to the unit behind the front bumper and i have signal on them (again, without oscilloscope i don't know the duty cycle and so on).
My guess is that the aux heater unit is broken. Haven't spend much more time on this, because AC has more priority.
I cleared them and the AC was still not working. I don't think they are linked, because AC worked and works even with these errors logged.

[Smac770]

The aux (air) heater grid placed in the heater core (ie, PR-7E6) is controlled by the HVAC control module, J255.

J364 is for the fuel driven aux (coolant) heater system, PR-9M9. Do you even have a J364; should be address 18. This is a later B8.0 example, after they started using C7 component.

Address 18: Aux. Heat (J364) Labels: 8R0-265-105.clb
Part No SW: 4H0 265 105 A HW: 4H0 265 105 A
Component: Standheizung H20 0230
Revision: 34003004 Serial number: 20100422102634
Coding: 5D2000
Shop #: WSC 06335 000 00000
VCID: 204415A9331E1D3B60-8075

No fault code found.

The J364 is built into the aux coolant heater, located in the front right of the engine bay.