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Thread: A/C Issue

  1. #1
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    A/C Issue

    All,

    I've done a bit of sleuthing, but no joy, so far. So, I'll throw it out to the community.

    I had the A/C serviced earlier this year, as it wasn't blowing cold. I assumed this happened because the car sits for long stretches while I'm out of town. Anyway, in the DC region, you cannot operate without A/C in the Summer. So, I had it re-charged and leak tested (again). No problems. Blew cold air.

    Car has sat for about two weeks.

    Took it for a 30min drive (mostly highway) today. A/C set to 70. Exterior temp in the low 90s. About 15-20min into the drive, the blowing-cold A/C (fan speed about 1/3 to 1/2) started blowing warm air and the temp-hold function started increasing fan speed to max. Shut it down. Turned it back on. Still blowing warm on max fan speed. Shut it down and rolled down windows.

    Got to my destination. Turned car off. Turned car on. Blew cold air. Shut it off and had my meeting.

    Turned car back on for return trip. Blowing cold air with fan speed about 1/3 to 1/2. Drove ~20min of 30min trip, and started blowing warm air (with increasing fan speed), again. Very odd, indeed.

    Shop thinks it might be problem with the interior temp sensor. Any thoughts?

    Also, FYI, on shut down, engine cooling fans are running for an extended period. I doubt it's related, but it's something that's only cropped up recently.

    Thanks,

    CW

  2. #2
    Registered User G2's Avatar
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    If luck is on your side the cooling fans running is likely due to failing ECT tensor. It's located at the right rear of the intake housing (when looking from the front).

    If that doesn't solve the issue, it's more than likely the Thermostat is stuck/failed. The engine temp gauge is NOT accurate. If the needed is even 1/2 a width beyond the normal line, coolant may be 25F too hot. The high speed fans will run. The low speed fan is all that should run at idle with the A/C off. Barely audible.

    The A/C system is able to shut down to help prevent the engine from over heating. It can and will do so in hot weather usually around 100-105 in our region. Dealt with a few cars that have the same problem- mine as well on one occasion years ago.
    -- If there are HVAC problems (DTC's) for the temp sensor, replace it. However try operating it on manual and not auto mode first. I never use auto-mode, too annoying. Doubt it's the temp sensor, however.

    Once the engine cooling issues are sorted try removing the bottom splash shield to help pump out the hot air. Normally it will help - at least for slower speed town driving. I don't do this (anymore) due to a low ride height and custom made IC duct exhaust air dam flaps and 3 additional cooling fans. Make sure there is minimal debris between the Condenser and Radiator. A good A/C tech will know what to check for in terms of pressure and temperature differentials. Simply charging the system to spec on these old cars does not take into account these aspects. I use pressures and temperatures - basically like an ECU tune, using various feedback based on the fundamentals of operation.

    Not to poke anyone on potential driving habits, but tail gating will most certainly reduce air flow at freeway speeds - and increase temps. Had an old VW (water cooled) back in the day that taught me that one. Make sure the engine is cooling correctly and go from there...

    Hope that helps
    Cheers, Gary-- ASE Master Tech; Auto Tech AAS; Amsoil T-1; Ex. Prototype Eng.; 30yrs exp.
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  3. #3
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    Mine did something similar with the max fan speed deal and then eventually fan no go at all and it was "blower motor resistor" and learned then its a common failure, funny looking thing with a bunch of prongs on it and electrical plug all about the size of your palm. May have nothing to do with the malfunctioning temp / not blowing cold though, I don't recall. I just know I thought I was in for a much more involved repair, like even if blower motor itself, and this resistor thing is super easy to change, its under glove box. Actually I bought a new Chinese ebay knockoff part first and it only worked for short while then I got a Audi used part from dismantler place and its worked for years since.

    Audi part # 4B0820521

    https://www.ebay.com/itm/SWAG-Heater...-/162611486803

  4. #4
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    Interesting suggestions, guys. Thanks. I will start keeping a list.

    Indy shop can't give me a service window until Aug 18. Crazy. Can't drive here for a month in the Summer without A/C, so it's going to have to go to the dealer (unless something opens up fast at the indy). Always good to have a game plan for them!

    Keep 'em coming!

    CW

  5. #5
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    Another thing that can happen when the A/C starts to get low on charge is that the evaporator will actually get too cold and the condensation will start to freeze. Eventually it gets frozen solid and won't effectively cool the air. After you shut it down, the ice melts and you get cooling again.

    In any case, you definitely have a leak somewhere. Sitting long periods should not cause significant loss of coolant charge.

    Some things to check, is the A/C compressor actually running when it's blowing warm? You need to get a clear view of the pulley to make sure the clutch is engaged to be sure. Also, if you stop when it's blowing warm and shut down, you should eventually get a big puddle of water under the car if the evaporator is iced up.

    Any decent A/C shop should be able to put gauges on it and tell if the charge is getting low again. I'd start with just checking that before digging deeper.

    Good luck!

  6. #6
    Registered User hahnmgh63's Avatar
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    I'm with GreggPDX on this one. I would check the Coolant charge. May be low, and if so that means something is causing a slow leak. My Audi's keep a charge for years so if it is low there is a leak. Fan speed just means that in Auto as the temp is going up (because it is longer cooling) that the Climate control computer is trying to increase fan speed to cool the car down. As Greg said, need to see if the compressor is running when it starts to get blow warm, if not it doesn't mean a bad compressor necessarily but could be the low pressure switch cutting in. It should be fairly simple to narrow down each component, pressure charge, A/C clutch, low pressure switch, etc...
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