C5 HVAC diagnostic menu + A/C mystery problem

[rollerton]

Summer is here so time for some A/C trouble.
Here's the deal: A/C shuts intermittently off, goes into ECON mode after maybe 20-30 minutes of driving on a hot day. Works pretty well up until then, no odd symptoms. After it quits, if you turn the car off for a minute or two and restart it the A/C will work momentarily then click back into ECON; the ECON setting doesn't do anything once it's quit.
Took it and had it checked for leaks and topped off. They found no problems of any kind. I have scanned every module and have only one error which is 'air quality sensor electrical malfunction' . I don't see how this could have any affect on the A/C. But it's suspicious.
So ...I assume I just have to start throwing money at it and hope I stumble across a problem? Without a error or even a symptom of an error ..where do I start...relay? Bypass Pressure switch? Shit.





But here's a long shot~~Does anyone know anything about the HVAC unit diagnostic menu? Press Recirc and ^UP vent button with key on and you get into the cryptic diagnostic menu for the HVAC.
I've been looking at this trying to figure out what some of the readings mean and they don't seem to always correlate with something that makes sense.


Here's a breakdown of how it's supposed to read,
I also have a copy with what the error codes translate too if they show up:

---------------------------------------------------------------------
Accessing On-Board Diagnostic codes
Press and hold the recirculation button. Then press the manual flow control up arrow. You should see a 1c. Press the temperature up ("+") or down ("-") buttons to select a code number. Then press the recirculation button again. The value should display. Press the temperature up or down button again to display another code.
NOTE: Air Flow Motor (V 71) and Potentiometer (G 113) are not installed in USA/Canada vehicles. Disregard values displayed for these components.

Code Displayed Value
1 System malfunction - displayed as a Diagnostic Trouble Code (DTC), see chart below

2 Digital value of Interior Temperature Sensor, in Headliner (G 86)
3 Digital value of Interior Temperature Sensor, in Instrument Panel (G 56)
4 Digital value of Fresh Air Intake Duct Temperature Sensor (G 89)
5 Digital value of Outside Air (Ambient) Temperature Sensor (G 17), front
6 Digital value of Outside Air (Ambient) Temperature Sensor
7 Digital value of Ambient Temperature Sensor At Fresh Air Blower (G 109)
8 Digital value of Temperature Regulator Flap Motor Potentiometer (G 92)
9 Delta value of Temperature Regulator Flap
10 Non-corrected specified value of Temperature Regulator Flap
11 Digital value of Central Flap Motor Potentiometer (G 112)
12 Specified value of Central Flap
13 Digital value of Footwell/Defroster Flap Motor Potentiometer (G 114)
14 Specified value of Footwell/Defroster Flap
15 Digital value of Air Flow Flap Motor Potentiometer (G 113)
16 Specified value of Air Flow Flap
17 Vehicle Speed (km/h)
18 Actual Air Blower voltage (Volts)
19 Specified Fresh Air Blower voltage (Volts)
20 A/C Compressor (A/C Clutch) voltage (Volts)
21 Number of low voltage occurrences, non-transient
22 Cycle condition of A/C Refrigerant High Pressure Switch (F 118)
23 Cyclings of the A/C Refrigerant High Pressure Switch (F 118)
24 Cyclings of the switches, absolute non-fluctuating
25 Analog/Digital value, Kick-Down Switch
26 Analog/Digital value, Engine Coolant Temperature (ECT) Warning Light
27 Coding value
28 Engine Speed (RPM)
29 A/C Compressor speed in rpm (Equals Engine Speed x 1.28)
30 Software version
31 Display check (all segments of A/C Control Head display light up)
32 Potentiometer malfunction counter, Temperature Regulator Flap
33 Potentiometer malfunction counter, Central Flap
34 Potentiometer malfunction counter, Footwell/Defroster Flap
35 Potentiometer malfunction counter, Air Flow Map
36 Feedback value, cold end-stop, Temperature Regulator Flap Motor Potentiometer (G 92)
37 Feedback value, hot end-stop, Temperature Regulator Flap Motor Potentiometer (G 92), max. stop
38 Feedback value, cold end-stop, Central Flap Motor Potentiometer (G 112)
39 Feedback value, hot end-stop, Central Flap Motor Potentiometer (G 112)
40 Feedback value, cold end-stop, Footwell/Defroster Flap Motor Potentiometer (G114)
41 Feedback value, hot end-stop, Footwell/Defroster Flap Motor Potentiometer (G114)
42 Feedback value, cold end-stop, Air Flow Map Motor Potentiometer (G 113)
43 Feedback value, hot end-stop, Air Flow Map Motor Potentiometer (G 113)
44 Vehicle operation cycle counter
45 Calculated interior temperature (internal software, in digits)
46 Outside (ambient) temperature, filtered, for regulation (internal software)
47 Outside (ambient) temperature, unfiltered, (internal software, in deg C)
48 Outside (ambient) temperature, unfiltered, (in digits)
49 Malfunction counter for speedometer (vehicle speed) signal
50 Standing time (in minutes)
51 Engine Coolant Temperature (ECT) in deg C
52 Graphics channel 1 - A/C compressor switch-off conditions are identified by illuminated segments of the “88.8� display. See chart below.

53 Graphics channel 2 - Climate system electrical outputs are identified by illuminated segments of the “88.8� display. See chart below.

54 Control characteristics
55 Outside (ambient) temperature, in deg C or deg F depending on setting on A/C control head
56 Temperature in deg C, from Interior Temperature Sensor, in Headliner (G 86)
57 Temperature in deg C, from Interior Temperature Sensor, in Instrument Panel (G 56)
58 Temperature in deg C, from Fresh Air Intake Duct Temperature Sensor (G 89)
59 Temperature in deg C, from Outside Air (Ambient) Temperature Sensor (G 17), front
60 Temperature in deg C, from Ambient Temperature Sensor At Fresh Air Blower (G 109)
61 Software version (latest)
-------------------------------------------------------------------------

[a4kamila6]

Does your aux a/c fan kick in right away when you put on a/c? Does it stay on the whole time?

[4rings2turbos]

Goes into ECON mode and won't allow you to take it out of ECON? Maybe look at the pressure switch if you can't find anything else.

[blkrhyno]

I'm having a similar issue, I had a unit from an 01 with the non peeling buttons in the car but it has an off button where the recirc button is on the regular units. So I put my old unit back in to see if the A/C would work but now the ECON button is stuck on and as far as I know this button shuts off the A/C compressor. The A/C worked before putting the non peeling unit in but when I put it in it was cold so I never tested the A/C. Tested the fans and they all work. Headed to the junk yard this weekend to pick up another unit and see what happens.

[4rings2turbos]

^that usually means the pressure switch is bad. Did you scan?

I might be wrong here, but I believe prefacelift and facelift controllers are not interchangeable aside from the button faces.

[rollerton]

^that usually means the pressure switch is bad. Did you scan?

I might be wrong here, but I believe prefacelift and facelift controllers are not interchangeable aside from the button faces.

^^ This is true. You can't swap the early/ late HVAC controllers or you get ECON mode.

Goes into ECON mode and won't allow you to take it out of ECON? Maybe look at the pressure switch if you can't find anything else.

Yeah..A/C sort of starts to warm up a little, then just 'click' and it's in ECON and you can't turn it off. Cycle ignition and A/C works okay momentarily then ECON again. It seems temperature dependent since it didn't happen until these hotter temps recently.

Does your aux a/c fan kick in right away when you put on a/c? Does it stay on the whole time?

Fans seem to work normally, engine temps starts to creep but has never gone barely a hair past 1/2 way.

[glennda5id]

What is the actual code you are getting from hvac computer when you scan with VCDS?

[rollerton]

What is the actual code you are getting from hvac computer when you scan with VCDS?

I'm pretty sure it's "01592 air quality sensor electric circuit failure" . Coolant tank sprung a leak, but I'll be looking into it some more this afternoon and scan some more things and check MBV for ...anything weird.
According to documentation that sensor shouldn't have anything to do with it..but again..suspicious.

[SteelyS6]

I have the exact same issue with my S6 and the same code for air quality sensor. I read somewhere that the G238 sensor by pollen filter can cause these issues. I will be replacing this sensor and will report back. I have had my a/c system checked and checks out ok.

[glennda5id]

Okay, so instead of using the HVAC diag, you can scan with VCDS, find the compressor off measuring block, and there should be a number. The number will match up with the issue from the list above you posted.

[glennda5id]

I think its measuring block 2.

[rollerton]

Okay, so instead of using the HVAC diag, you can scan with VCDS, find the compressor off measuring block, and there should be a number. The number will match up with the issue from the list above you posted.

That's part of what I'll be doing this afternoon I guess. Hopefully I can figure something out.

[Audibot]

Perhaps by time you've driven those 25-30 minutes, and the pressure has built up to the point the pressure switch thinks it's too high and shuts it down. That would also make sense that after cooling down a couple minutes it briefly goes on before swapping back to ECON.

[glennda5id]

Sorry, here is the compressor off code. It is not the list above

- 0 = Compressor ON
- 1 = Compressor OFF: Refrigerant Pressure too high (> 32 bar)
- 2 = compressor OFF: Basic setting not performed
- 3 = Compressor OFF: Refrigerant Pressure too low (< 2.0 bar)
- 5 = Compressor OFF: Engine Start Detection
- 6 = Compressor OFF: ECON Mode active
- 7 = Compressor OFF: A/C System / FAN OFF
- 8 = Compressor OFF: Outside Temperature too low (< 3.0 °C)
- 10 = Compressor OFF: Vehicle System Voltage too low (< 10.1 V)
- 11 = Compressor OFF: Engine Temperature too high (> 118 °C)
- 12 = Compressor OFF: Shut-Off requested by Engine Control
- 13 = Compressor OFF: Vehicle System Voltage too high (> 17 V)
- 14 = Compressor OFF: Evaporator Temperature too low
- 16 = Compressor OFF: Compressor Activation faulty
- 17 = Compressor OFF: No or implausible Signal Pressure Sensor
- 18 = Compressor OFF: Vehicle Speed Shut-Off
- 19 = Compressor OFF: Shut-Off requested by Central Electronics Control (Load Management)

[rollerton]

May have found the issue. Main AUX rad fan doesn't seem to come on reliably. The exterior fan (small one on front) comes on, but the other one doesn't come on, and I can't seem to make it run in output tests.
So, just need to narrow down whether it's the control module {seems unlikely since there are no faults?} or the fan itself. A/C will run great and I wasn't able to make it turn off yet today, but will update after I get a chance to jump 12V to the fan to see if it runs.

[a4kamila6]

May have found the issue. Main AUX rad fan doesn't seem to come on reliably. The exterior fan (small one on front) comes on, but the other one doesn't come on, and I can't seem to make it run in output tests.
So, just need to narrow down whether it's the control module {seems unlikely since there are no faults?} or the fan itself. A/C will run great and I wasn't able to make it turn off yet today, but will update after I get a chance to jump 12V to the fan to see if it runs.

Thats the first question I asked lol. Give the fan 12v and see if she spins. My aux fan died last month, just got a new one from europa for 120 shipped.

[glennda5id]

The HVAC module is turning off the compressor for a very specific reason. If it was due to high temp which might lead to high pressure then you would have AC for atleast a little while. Did you check meaure group 002 or whatever the compressor off group is?

[rollerton]

Thats the first question I asked lol. Give the fan 12v and see if she spins. My aux fan died last month, just got a new one from europa for 120 shipped.

Yeah. That fan does run intermittently, it just seems to NOT run when you need it most , when the temp gauge gets above 1/2. I checked it 3 days ago and it was running w/ A/C on but now it quits when it gets very hot.
Without a module error in leaning towards fan failure.

Did you check meaure group 002 or whatever the compressor off group is?

I did check MBV for all the HVAC readings and they were all withing spec; of course that was when the engine was running at normal temp and the A/C was working just fine. I messed around for about a half hour and it never quit BUT the fan didn't kick on today while I had access to the car. But output tests also couldn't trigger the fan. It was a couple hours later in traffic I got a call that it quit again.
Gotta be the fan. I'll narrow it down in the tonight or in the a.m.
The 4.2 fan is the same as the 2.7? It's just an electric motor can't be too fancy. What's wrong with the cheap ones from Amazon? It's not "my car" technically even though I'll probably inherit it before long. So awesome OEM parts aren't totally required for every breakdown and just had to order a coolant tank for it at $95.
The a/c fan is 4b3 xxx... and the rad fan is 8D0xxx455R ?

Amazon Fan #1

Cheaper Amazon fan #2

[ImAudiHeree]

I'm not sure if on the 4.2s if you can give them 12v to test them. On my b6 s4 I had a ground and a signal wire not a power wiring kind of odd I must say so when I tried bench testing it I could not make fan move. I then turned my attention to fan module which should intermittent issues and then I went all he way back and found out fuse had blown. Replaced fuse ac perfect ever since.