Using OBD2 port adapter to check air conditioning

Discussion in 'Clarity' started by sabasc, Apr 25, 2021.

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  1. Hi everyone,
    Similar to the Budget Battery Capacity Readout thread started by@MrFixit I'll start a thread on using OBD2 port adapter and software to check air conditioning status, and if possible from the data available perhaps diagnosing faults.

    What I have:
    I'd like to update this thread as we learn more about what info the car is providing in its communication with Car Scanner Pro. Please reply with any information you may already have.
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  3. MrFixit

    MrFixit Well-Known Member


    While your cooling is dead, it would be especially appropriate to look at your data. Normally, if a vehicle has at least some liquid refrigerant in the system, you will measure the 'saturation pressure' for that refrigerant when the system is OFF and stabilized at a known temperature (for instance while parked in your garage, and not running). Here is a chart of the saturation pressure for the R1234yf refrigerant that is used in the Clarity:


    If your pressure does not 'agree' with this chart when the system is OFF at a specific temperature, then you are OUT of Freon and there is no point in any further testing until the leak has been identified and the system has been re-filled. You should not even operate the system under these conditions...

    If your static pressure is OK, then it would be time to do more evaluations with the system running. This is where it would be useful to collect data from other Clarity's with working systems for comparison. If you have some Freon, but it is too low, then this pressure will drop dramatically when the system is engaged (and the compressor will cycle on and off too frequently). You would see the pressure going up and down every few seconds.

    A normal system would hold a steady pressure and cycle maybe only once per minute. I would like to encourage those who have Car Scanner working (and live where it is currently hot) to aim for the following data...

    1. Set the inside temperature to 75 Degrees.
    2. Operate the A/C while on a steady drive for enough time to stabilize at this temperature.
    3. Note (with Car Scanner) the actual inside temperature, the actual outside temperature, and the pressure.
    4. We should be able to get a 'family of data'... All with 75 degrees inside, and with a variety of outside temperatures (in the range of 80-100 degrees for instance).

    I would like to assist with this process, but can't for another month or-so because it isn't warm enough here quite yet...

    If you have a chance, please give this a try and share results here !
    Pegsie and sabasc like this.
  4. Thanks @MrFixit
    I'm still getting acclimated to the car scanner pro features. I haven't yet determined where to find the parameters you're looking for. In the saved data I see temperatures listed but they seem to be in Celsius regardless of my having set temperature to Fahrenheit.

    I didn't explicitly request that car scanner save my data, but it seems to have done so but only saved a partial list of all the possible metrics to collect, specifically It seems to lack "saturation pressure".

    Once I have that parameter, I assume it should fall in the middle column, or lower end of the left column in the chart. Should I expect to need to convert the saturation pressure value or just look it up directly in the chart, for ordinary ambient temperature?
  5. MrFixit

    MrFixit Well-Known Member

    @sabasc :

    Let me clarify something for you (and probably others)...

    If you set up your Vgate adapter and install Car Scanner, there will be a Clarity PHEV profile available. @lincomatic and I provided that profile to the Car Scanner developer, and he added it. It contains much of what you might be interested in (most importantly the battery capacity) BUT it does NOT contain any of the example dashboards that we created. That's OK - you can make your own dashboards to suit your needs.

    There is another drawback in going this route however... We have added some parameters (including the A/C pressure) and we have not provided these additional parameters to Car Scanner yet, so you won't see them there...

    The best way to have the latest parameters (including the A/C pressure, and the dashboards that show it) is to use our 'backup set' for Car Scanner. This is provided in the original thread as a /zip file here:

    You download this .zip file, extract the files, and get them on your phone. In Car Scanner, in the settings area, you can import a backup file. This will bring in ALL of our known parameters, as well as the example dashboards that use them. You can see the 5 dashboards posted with the .zip file. The 5th dashboard shows inside, and outside temperatures as well as the A/C pressure.

    If you can get this working and see the A/C pressure parameter on the appropriate dashboard screen, you should be good to check this out. There is no conversion needed... You simply look up the pressure on the table that corresponds to the stable ambient temperature and it should 'match' the value that you read from the car as A/C Pressure. Remember however, there are tolerances here. The temperature sensor in the car has a tolerance, and the pressure sensor has a tolerance, so it will not be 'exact'. It should be pretty close however.

    If we uncover more parameters of interest, I will always post them as a 'backup' set in the original thread. We have not established if / when we will provide additional parameters to Car Scanner. So, if you want the latest ones, you should always go with the backup set posted in this forum.
    ClarityDoc, TomL and sabasc like this.
  6. MrFixit

    MrFixit Well-Known Member

    I will start the ball rolling with actual data (still too cold here to run the A/C, but soon)...
    I have two different conditions for my static saturation pressure measurement.

    1. Inside / Outside temperature 59F, A/C Pressure 57.7 psi
    2. Inside / Outside temperature 64.4F, A/C Pressure 66.4 psi.

    It just so happens that in this temperature range, the saturation pressure (psi) is approximately equal to to the temperature (Fahrenheit). That will change as the temperature goes up as you can see from the table in Post #2.
    sabasc likes this.
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  8. Thanks @MrFixit for the additional info.

    I forgot to mention in my Wednesday post above that I was using your backup from March. Thanks for the updated backup file for car scanner. That did the trick.

    I definitely don't have any refrigerant!

    I was also able to find the corresponding readings readings in the Data recording section. It was good to see I don't have to have an active connection to the car (so I can use the Dashboard) to access this info.

    Attached Files:

  9. MrFixit

    MrFixit Well-Known Member

    Wow, you are dead as a door-nail !

    Sometimes a dealer is tempted to just recharge the system rather than take the time to properly locate and repair a leak. You can never be sure whether your refrigerant leaked out gradually over 3 years, or did a severe leak develop suddenly... In any event, it is clear that there is a leak which must be repaired.
    sabasc likes this.
  10. MrFixit

    MrFixit Well-Known Member

    I was able to get some data today

    Vehicle was parked in the sun, so it was quite hot inside when we started...
    We engaged the A/C right away, with inside temperature set to 75 degrees.
    We drove for maybe 40 minutes, but Car Scanner stopped recording after the first 10 minutes (auto power-off?)

    1. Temperature readings are pretty granular. Likely because OBD only reports integer Degrees C, so one step is 1 Deg C, or 1.8 Deg F.
    2. Outside temperature throughout drive was very stable at 88 Deg F (at least within one step, 1.8 Deg F).
    3. Inside temperature came down just fine, BUT clearly this sensor does not represent the cabin temperature very well. The inside temperature did become stable (at around "89" as recorded by the sensor). It was very comfortable inside however, and I believe the actual temperature was more in line with the 75 Deg set-point. The air from the vents was very cool. I don't know where the inside temperature sensor is located.

    With our Clarity, For an outside temperature of 88 Deg F, and an inside set-point of 75 Deg F, the A/C pressure runs at 140 psi once everything stabilizes. I have no objective measure, but I believe this system is working properly. The inside sensor does not seem to match reality however.

    LegoZ, TomL and sabasc like this.
  11. vicw

    vicw Active Member

    @MrFixit - You have again provided something for me to obsess over regarding the health of my 2018 Clarity. Thank you for the chart and the means of capturing the data.

    I just measured my static saturation pressure, with the A/C turned OFF.

    Inside/Outside temperature 87.8f., Pressure 89.92 psi

    If I'm interpreting my data on your chart correctly, I should have had a pressure around 102 psi, so mine is currently about 12% lower than optimum. So far, my system seems to be providing sufficient cooling, so I'm hoping that pressure deficiency, or loss, is a nominal, long term pressure loss, and not a cliff I'm about to go over. In any case, that reading gives me a good reference going forward
    sabasc likes this.
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  13. MrFixit

    MrFixit Well-Known Member

    you have an interesting scenario...
    Your pressure does seem too low, but we are just at the start of investigating this.
    Thanks for the input...

    Keep us posted going forward. I have a feeling this is the time of year (when people just start using their A/C for the first time this season) we will see multiple reports of 'failed' systems,
    sabasc likes this.
  14. MrFixit

    MrFixit Well-Known Member

    Just adding this plot to visualize data collected so far...
    AC Plots.png
    sabasc likes this.
  15. Danks

    Danks Active Member

    Not sure if I did this correctly.
    1. I turned the car on with Climate turned off
    2. I checked with Car Scanner and got
    Inside temp = 68
    Outside temp = 59
    AC psi = 62.08
    sabasc likes this.
  16. It looks like it fits nicely on the curve above! I wish to have my Clarity AC rise to that curve. It's lonely down there on the zero line.
    Hopefully the dealer will have a diagnosis and I can get a repair done soon.
  17. MrFixit

    MrFixit Well-Known Member

    Yes... That's OK for static. It is 'best' if the inside and outside temperatures are equal, but that really only happens at night or in a garage. If there is a difference between inside and outside, it seems like the lower one is the most relevant.

    AC Plots.png
    sabasc and Danks like this.
  18. MrFixit

    MrFixit Well-Known Member

    A plot update with new operating data from @vicw:
    AC Plots.png
    sabasc likes this.
  19. vicw

    vicw Active Member

    Cooler weather here for the last couple of days, so I was able to capture a couple of recent data points:

    Static A/C Pressure
    Temperature IN & OUT: 69.8F
    A/C Pressure: 72.81 psi

    Operating A/C Pressure
    Temperature OUT: 71.6F
    Temperature IN: 75.2F
    A/C Pressure: 95.29 psi

    The static pressure which I reported back on May 4th, at about 88F, which was somewhat below the predicted curve, has me concerned that I might have a possible slow pressure leak on my system, so I'm also capturing date and times on my record of the data.
    sabasc likes this.
  20. MrFixit

    MrFixit Well-Known Member

    Updated Plot - @vicw right on the static curve this time...:
    AC Plots.png
    vicw and sabasc like this.
  21. Hopefully some Clarity owners from the south can get us more data points with higher ambient temperatures?
    My car is being fixed as I write this. I will get a new reading immediately after taking delivery, which will give us another northeast (Massachusetts) reading.
    @MrFixit I see you have two static data points on the graph but I only one operating data point. Is that expected?

    To ease some burden on you funneling our data, would it be feasible to post the graph and input (spreadsheet?) as a Google Sheets document and share it so we can post our own data? I realize we probably aren't going to get a tsunami of data but the graph will (hopefully) get more busy as the nerds among us check frequently. I especially plan to given that my car will soon be repaired, i.e. check for post-repair pressure decay (leaks).
  22. MrFixit

    MrFixit Well-Known Member

    Static measurements are unrelated to operating ones. I can walk out to my garage any day and take a static measurement at whatever ambient temperature it happens to be that day. For an operating measurement, I need a day that is hot enough for me to operate the A/C while driving for a while in order to reach a stable condition. It has been unusually cool here and I have only had one opportunity so far to obtain a reading while operating.
    I'll look at doing the equivalent of this in Google Sheets. I currently use a somewhat obscure, but powerful open source tool called "Veusz".
    sabasc likes this.
  23. vicw

    vicw Active Member

    Regarding the static measurements, I've been limiting my data to report only when the Inside and Outside temps are identical, typically most likely to be at the beginning of the day, when the car has not been operated for quite a few hours, and the temps have equalized. I don't know if that really makes any difference to the result, but it's one less variable to worry about.
    sabasc likes this.

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