VCDS data interpretation question (re: air conditioning issue)

[aroby]

I went to look at a 2015 S4, which had some cosmetic issues with it, but also turned out the AC wasn't working. This car is at an Acura dealership and they took it as a trade in, said they done they're million point inspection bla bla bla. They said the AC was working, but when I tested it the AC light would turn on, then off, which is indicative of the compressor not starting. There was no CEL on the vehicle. Anyway, their service guys hooked it up to their gauges and I was told that they added refrigerant and a dye to check for leaks and there were none from the evaporator, the compressor or the condensor. Not sure how they would have checked the evaporator in the 40 mins they were working on this!

Sure enough, the AC was working. I used VCDS to check out the diagnostic codes and, sure enough, the HVAC was alerted - it had gone over temperature twice in the past couple of weeks. What caught my eye though, was the this alert had been dismissed 33 times. The dealer wouldn't accept my offer for the car nor would they negotiate, so I walked.

Would I be correct in thinking that this AC needs much more than refrigerant? Seems that it was not working correctly, the past owner likely added refrigerant, reset the CEL but didn't clear the diagnostic codes, the dealer said looks fine, we'll accept the trade in and two weeks later the refrigerant has leaked out?

[OLDS4]

Sounds like walking away was the right thing to do.

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[SwankPeRFection]

Could be the compressor is bad, but what was the specific code?

[Smac770]

The MIL is set for emissions related and other critical drivetrain concerns. You're not going to get a MIL for a comfort system like the climate control system.

You have a VCDS scan of the vehicle but that scan is not posted. So none of us know what information you're working from.

[aroby]

We ran an Auto Scan and it showed the following:

08-Auto HVAC -- Status: Malfunction 0010


Address 08: Auto HVAC (J255) Labels:. 8Kx-820-043-3Z.clb
Part No SW: 8K1 820 043 AQ HW: 8K1 820 043 AQ
Component: KLIMA 3 ZONEN H04 0122
Revision: C1000000 Serial number: 01290820140106
Coding: 6600228000
Shop #: WSC 06325 000 00000
VCID: 77ABEBC16FCEBA63DA8-8022

1 Fault Found
00256 - A/C Pressure/Temperature Sensor (G395)
002 - Lower Limit Exceeded - Intermittent
Freeze Frame:
Fault Status: 00100010
Fault Priority: 2
Fault Frequency: 2
Reset counter: 33
Mileage: 103925 km
Time Indication: 0
Date: 2023.04.01
Time: 11:03:26

Freeze Frame:
Temperature: 17.0°C
Temperature: 14.0°C
Load: 0.0 %
Absolute Pres.: 1.6 bar
RPM: 1680 /min
Speed: 0.0 km/h
Current: 0.000 A
Temperature: 14.0°C

[SwankPeRFection]

Everything points to the pressure sensor for this from the looks of it.

[aroby]

Everything points to the pressure sensor for this from the looks of it.

But that doesn't explain the disappearance of refrigerant, but maybe it was a combination of things. Any idea where I can determine what the fault status bits mean?

[SwankPeRFection]

But that doesn't explain the disappearance of refrigerant, but maybe it was a combination of things. Any idea where I can determine what the fault status bits mean?

Some of those switches/sensors would leak. There’s a TSB for leaking sensor but it doesn’t apply to your model year. That’s not to say it’s impossible for it to do it. For the $40 it costs, it’s worth replacing it… if someone’s messed with it before, it’s not hard to mess up the threads on the fitting it screws into, just FYI.

[Smac770]

The DTC just says the value is low. If the refrigerant is actually low, then the G395 would seem to be working correctly. It seems you simply have a leaking refrigerant circuit and you need to determine the leak location and correct that, in whatever normal manner one does leak isolation in an A/C refrigerant circuit (something about UV dye and glasses?).

The sanity check for the pressure level is A/C off, engine running, G395 should report the follow bar(psi) or more at the following ambient temp C°(F°):
15 (59) - 3.0 (43.5)
20 (68) - 4.0 (58)
25 (77) - 5.0 (72.5)
30 (86) - 6.0 (87)
35 (95) - 7.0 (101.5)

Only 1.6 bar at around 15°C, would seem short on refrigerant. Though you can only know if the refrigerant was low by evacuating the system and seeing how much weight was pulled out compared to how much weight is spec for reload.

If you do change out the G395, don't forget to coat the o-ring with appropriate refrigerant oil.

[aroby]

The DTC just says the value is low. If the refrigerant is actually low, then the G395 would seem to be working correctly. It seems you simply have a leaking refrigerant circuit and you need to determine the leak location and correct that, in whatever normal manner one does leak isolation in an A/C refrigerant circuit (something about UV dye and glasses?).

The sanity check for the pressure level is A/C off, engine running, G395 should report the follow bar(psi) or more at the following ambient temp C°(F°):
15 (59) - 3.0 (43.5)
20 (68) - 4.0 (58)
25 (77) - 5.0 (72.5)
30 (86) - 6.0 (87)
35 (95) - 7.0 (101.5)

Only 1.6 bar at around 15°C, would seem short on refrigerant. Though you can only know if the refrigerant was low by evacuating the system and seeing how much weight was pulled out compared to how much weight is spec for reload.

If you do change out the G395, don't forget to coat the o-ring with appropriate refrigerant oil.


Thanks for taking the time to provide all that detail! I'm not going to proceed with this car, but learned a lot for future reference.

[akop18]

The DTC just says the value is low. If the refrigerant is actually low, then the G395 would seem to be working correctly. It seems you simply have a leaking refrigerant circuit and you need to determine the leak location and correct that, in whatever normal manner one does leak isolation in an A/C refrigerant circuit (something about UV dye and glasses?).

The sanity check for the pressure level is A/C off, engine running, G395 should report the follow bar(psi) or more at the following ambient temp C°(F°):
15 (59) - 3.0 (43.5)
20 (68) - 4.0 (58)
25 (77) - 5.0 (72.5)
30 (86) - 6.0 (87)
35 (95) - 7.0 (101.5)

Only 1.6 bar at around 15°C, would seem short on refrigerant. Though you can only know if the refrigerant was low by evacuating the system and seeing how much weight was pulled out compared to how much weight is spec for reload.

If you do change out the G395, don't forget to coat the o-ring with appropriate refrigerant oil.Smac, as always, is the best. Everything to the absolute finest detail. Props smac. I'm sure I'll need your insight some day lol.

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