Diagnosing air con problem

[dblube]

Hi All,
First post here, got quite a strange air-con problem that I'd appreciate any help diagnosing. Car is a 2003 A4 B6 1.9tdi (engine code AVF). Have just replaced the G65 pressure sensor to no avail. Here are the symptoms:

• Air con worked last year, but this year was blowing warm.
• Had not been re-gassed since I owned the vehicle (5 years) so had system professionally re-gassed using an automatic machine that flushed, tested, lubricated and re-filled.
• Immediately after the re-gas the air con was still blowing warm air, both when vehicle stationary and under motorway driving.
• Fuses on box by drivers side door all intact.
• ECON light off (but goes on if I disconnect the G65 pressure sensor or corresponding 5A fuse).
• VCDS lite not reporting any relevant fault codes (codes re engine mount and steering angle sensor assumed irrelevant). The first time I checked this a few days ago I got no faults. I thin re-checked and got an "00819 high pressure sensor (G65) 29-10 short to ground - intermittent", so I replaced the sensor with a brand new hella-behr part. Thinking about it I was pulling the fuses to check if the econ light went on/off, this may have been the cause of the fault code.
• Auxiliary fan not coming on, voltages at the 4-pin fan connector next to the PS reservoir don't change when I switch ECON on/off.
• No drop of engine revs when I switch ECON mode on/off.
• Air con comporessor pulley seems fine, can't see or hear any problems.
• VCDS reports a Refrigerant Circuit Pressure of 5.0 bar and a High Pressure Signal (G65) of 20.5% at about 18C ambient temp, which according to VCDS is about right.
• G65 pressure sensor replaced, fault codes cleared, air con still not working, no aux fan etc.
• VCDS compressor shut-off criteria: all 0.0
• VCDS Compressor torque status: 0, Required Engine Torque: 2.0 Nm

Based on the above I think this means:

• The aux fan is not the problem. If it was, the air con would still blow cold under motorway driving (as in this thread)
• The G65 sensor may have been faulty, but now it certainly isn't.
• The compressor is not starting.

A few things I was wondering:

• How to work out if the compressor is faulty? I'm assuming this does not throw a fault code, i.e. the car does not actually know if the compressor is running or not.
• If the compressor was faulty, wouldn't the aux fan come on anyway? If so this makes me think the compressor is not faulty and something else is causing it to not start.

As you can see I have done a fair bit of diagnosis and probably replaced the G65 sensor for no reason, so any help would be appreciated!!!

[kite]

Is the clutch on the compressor pulley working ?
When you toggle the 'econ' setting you should get the pulley clutch engage/disengage.

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[dblube]

Thanks. When I turn ECON on I notice no change whatsoever in engine RPM which leads me to believe compressor is not engaging. As I said looking at the pulley it all seems in order and the compressor is not making any strange noises.
Are there any other checks I can do? I have a decent multimeter and VCDS lite.

[kite]

You might not get a change in engine revs, should hear a click as the clutch engages.


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[dblube]

OK thanks a lot for your help. I think I'm going to jack up the car, remove the undertray and listen for the compressor and possibly check voltage at the compressor connector. If both of those check out then I'll probably try to remove and inspect the pulley. My hunch is the pulley is shot.

[abyrne153]

The pulley clutch is permanently engaged on these. Check that the plastic hub on the front of the pulley doesn't spin freely as if it does then it needs replacing. These are not like other cars where you hear the clutch clicking in when the aircon comes on.

[dblube]

So I finally got under the vehicle, removed the belt and tensioner, undid the 3 long bolts that hold the compressor on, let it hang down supported by a few wooden blocks. Pulley spins freely, and the front of it seems to be missing completely! Attached picture shows what I found. The light grey part is actually plastic. The question is can I replace the missing part or have I got to buy a whole new pulley? If it's the latter I might try to make my own front plate. Can anyone tell me what the missing part looks like?!


20170729_161501.jpg

[Lozzy90]

This is exactly the same problem I had. Your missing a metal cover that just bolts on. I managed to get one from a Audi breakers off a knackered compressor for a couple of quid. The bolts tend to come loose an fall out, I put some locktite onto a new bolt when fitting a new cover back on. The attached picture shows what your looking for.
$_3.JPG

[dblube]

Awesome thanks! In fact I have been doing a bit of digging since my last post.

I found this listing and this one selling the whole pulley, and this one selling just the hub. But 60 quid for a pulley or 30 quid for the hub seems a bit steep to me for such a simple part.

Based on the part numbers in these listings, it looks like the following DENSO compressors all use the same hub / face plate:
6SEU12C, 6SE12C, 7SEU16C, 7SEU17C

Searching on ebay it looks as though these cross-reference to the following part numbers:

Mercedes:
a0002305911, a0002307911

VAG:
06C35907, 01E02713, 04C02678, 600820803
4B0260805M, 8E0260805M, 4B0260805K, 8E0260805N, 8E0260805AH, 8E0260805D, 8E0260805T, 8E0260805, 8E0260805AB, 4B0260805G
447300-9590, 447220-8404, 447220-8422, 447180-5374, 447220-8401, 447180-5373, 417180-5370, 447220-8421, 447170-7930, 447170-9090,
447220-8683, 447170-9091, 447220-8420, 447180-4290, 447180-5350, 447220-9600, 417180-5350, 447180-5356, 447220-8402, 447180-5352,
447220-8400, 447170-7931, 447170-7911, 447170-7912, 447180-5371, 447180-5372, 447170-7932, 447170-7933, 447220-8424, 447220-8682,
447220-8403, 447180-4280, 447150-0100, 447180-4270, 447220-8423, 447180-5370, 447220-8680, 447180-6720, 447180-5351, 447170-7910,
417170-9090, 447180-6740, 447220-8681, 447220-8222, 447220-8813, 447180-3203, 447300-8821, 447220-8230, 447220-8351, 447220-8193

Basically it looks as though pretty much any Merc / VW / Audi / Seat / Skoda (maybe even Subaru) from from early-mid 2000s used one of these. It apears that as long as the compressor matches one of the above part numbers and has the funny rounded-square hub on the front of the pulley it will probably be right (even if the pulley is slightly different diameter or has a different number of grooves). I found an old VW compressor on ebay for £15 delivered. If my reasoning is correct the hub should fit - will post back with results!

There are other very similar DENSO numbers that may also fit - if anyone knows any better please post compatible Denso numbers that have the front plate.

[dblube]

Problem solved - cold air at last! Just to confirm the hub was the same on the compressor I bought, even though the pulley was different diameter and number of grooves.
Thanks for everyone's input. Hope others find this thread useful. Cheers.