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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old April 27th, 2009, 18:52   #1
WestMass
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Default Air conditioning troubleshooting.

Winterís over, and Iím having A/C issues. Before I go any further, many thanks to DanG144 for the detailed fan and A/C troubleshooting guides I found while trying to diagnose my A/C.

I have a 2002 Jetta ALH with manual A/C. Hereís what Iíve found so far:
  • 344mm radiator fan had failed, so I replaced it with a new one. Both fans now work on low and high speed by jumping the pins in the radiator cooling fan thermo switch.
  • The fans do not work on low speed when the ignition, AC and interior fan switches are switched on. All the fuses on top of the battery and in the interior fuse block are fine. However, when I REMOVE fuse #S16 from the interior fuse block, the fans run on low speed with the ignition on. Is this normal?
  • All the tests for power and grounding on the 4 and 14 pin connectors to the fan control module J293 from DanG144ís troubleshooting guide appear OK.
  • I do have 9.5 volts at the connector at the compressor with the engine running and AC switch and interior fan on, however the compressor clutch doesnít engage. If I provide battery power directly to the compressor with the engine off, I can hear a ďclickĒ from the coil.
  • Yes, the dash switch illuminates and the interior fan works fine.
My best guess is that I need a new fan control module (J293) and a new clutch and clutch coil for the compressor. If I do need the coil and clutch, Iíd like to try and replace the clutch and coil on the compressor without breaking the A/C lines. Is that possible? (if I have to break the lines, Iíll probably throw in the towel and take it to the shop and let them do it.) Where can I find the spanner needed to remove the clutch/coil assembly?


What might I be missing? From the details provided, have I come to a reasonable conclusion? I donít have a ďduty cycleĒ meter, so I canít test the pressure sensor G65 as detailed in the troubleshooting guides referenced above. I've seen the J293 fan control module on Ebay for about $45, but that price seems incredibly low even compared to other online retailers. Too good to be true?


Thanks for taking the time to read thisÖ
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Old April 27th, 2009, 20:48   #2
whatnxt
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Might try here for parts:

http://www.autohausaz.com

I ordered a MAF for my MB and it was OEM for a lot less.
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Old April 28th, 2009, 14:46   #3
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Quote:
Originally Posted by WestMass
Winter’s over, and I’m having A/C issues. Before I go any further, many thanks to DanG144 for the detailed fan and A/C troubleshooting guides I found while trying to diagnose my A/C.

I have a 2002 Jetta ALH with manual A/C. Here’s what I’ve found so far:
  • 344mm radiator fan had failed, so I replaced it with a new one. Both fans now work on low and high speed by jumping the pins in the radiator cooling fan thermo switch.
  • The fans do not work on low speed when the ignition, AC and interior fan switches are switched on. All the fuses on top of the battery and in the interior fuse block are fine. However, when I REMOVE fuse #S16 from the interior fuse block, the fans run on low speed with the ignition on. Is this normal?
  • All the tests for power and grounding on the 4 and 14 pin connectors to the fan control module J293 from DanG144’s troubleshooting guide appear OK.
  • I do have 9.5 volts at the connector at the compressor with the engine running and AC switch and interior fan on, however the compressor clutch doesn’t engage. If I provide battery power directly to the compressor with the engine off, I can hear a “click” from the coil.
  • Yes, the dash switch illuminates and the interior fan works fine.
You have made an excellent, detailed and concise post. Good troubleshooting.

I noticed that my fans also came on unexpectedly when fuse S16 was pulled, during some of my testing while writing the troubleshooting guide. They came on once or twice, then did not come on again after that. Still working on exactly why. It looks as if power for the slow speed relay was coming in from some alternate source.

Your testing has proven that the FCM relays for running the fans work (both high and low speed relays). The relays are often the source of FCM failure.

The High speed fan operation is requested by the thermoswitch, but must come through the FCM, so that means the high speed relay is working.

The low speed fans coming on when you pull S16 is initiated by the FCM, so the low speed relay works as well.

Try unplugging the clutch connector at the compressor, then turning on the AC and fan, with the key on and see if your fans work. We are checking for a bad coil possibly dragging down the voltage on the fan control module. If the fans do not work in this test, then I would agree that you probably need a new fan control module.

Can you measure your AC clutch's electrical resistance? It should be somewhere near 4 ohms (or at least mine is.) While you are there, verify pin 2 of the harness plug has a good ground.

You did not say if you momentarily put battery voltage on the clutch (pin 1+, pin 2 grounded) with the engine running to see if it engages. I take it you tried it with the engine off? Try it, just for a second, with the engine on, and see if it will engage. I am a firm believer in "belt and suspenders" - I like to test several ways before spending money. If the resistance is good, and it works when full voltage (14.3 or so) is put across the coil, then I would replace the FCM first. A bad connection in the FCM, which is normally providing power to the clutch, could be the sole problem - when unloaded (as when measuring the output voltage at the compressor) the voltage would be 9.5, but it might drop when a normal load is placed on it.

Thanks for getting my attention with the email.

Dan


Quote:
Originally Posted by WestMass
My best guess is that I need a new fan control module (J293) and a new clutch and clutch coil for the compressor. If I do need the coil and clutch, I’d like to try and replace the clutch and coil on the compressor without breaking the A/C lines. Is that possible? (if I have to break the lines, I’ll probably throw in the towel and take it to the shop and let them do it.) Where can I find the spanner needed to remove the clutch/coil assembly?


You can and should replace the clutch and coil without breaking the refrigerant lines.

I do not have a source for the spanner. I'll see what I can find. Maybe someone else can put in their two bits worth here...

Quote:
Originally Posted by WestMass
What might I be missing? From the details provided, have I come to a reasonable conclusion? I don’t have a “duty cycle” meter, so I can’t test the pressure sensor G65 as detailed in the troubleshooting guides referenced above. I've seen the J293 fan control module on Ebay for about $45, but that price seems incredibly low even compared to other online retailers. Too good to be true?


$45 seems very low. I think you are wise to take it with a grain of salt. Anyone have any experience here?
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Old April 29th, 2009, 11:42   #4
WestMass
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Thanks for the quick reply Dan, lots of good information.

When I unplug the connector at the compressor with the AC, interior fan and ignition on, the fans do not work. In fact, the only time the fans have worked is when I shorted the thermoswitch or removed fuse S16 from the interior fuse block.

Resistance across the clutch coil is about 3.5 ohms. Voltage is 9.5 at the compressor connector with the engine running and AC, interior fan on. Wire 2 at the connector has a good ground, a fraction of an ohm on my old Micronta 22-220A analog multimeter.

With a pin through the white wire on N65, I get 1.5 volts ac and .64 volts dc with my analog meter. I donít have a duty cycle meter.

Last night I tried putting battery voltage across the coil for about 15 seconds (before I read your post) to see if the clutch would engage. It did, but it sounded very anemic, not the horsepower robbing drag that a good working compressor would produce. With the engine off, the clutch plate spins easily inside the pulley. This leads me to believe the compressor is probably shot. Does that sound true to you? I suspect the trouble with the fans has been lurking under the hood for a while, and resulted in the increased wear you described in your troubleshooting guide. (in fact, while driving around in the winter here the last think I want to happen is the fans turning on!) I searched for a clutch and coil assembly yesterday, but found new Sanden compressors for less than just the coil and clutch assembly.

Iíll go ahead and order a FCM and put that in place to hopefully resolve the fan issue before tackling the compressor. I would rather purchase and install it myself to save the parts markup and labor, then have a shop purge and refill the system.

Thanks again for your time and valuable info Dan, itís been a great help. Any other thoughts you might have would be appreciated. As I move forward with this, Iíll post the results.

Al
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Old April 29th, 2009, 13:56   #5
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A low refrigerant pressure, with everything else working properly, will lock out the low speed fans and the clutch. Of course you should not get the 9.5 volts to the clutch when you measure it, if this is the problem.

A low refrigerant pressure would also cause the compressor to have a low load.

If you had told me all of the same details that I now have, EXCEPT you did not have the 9.5 volts to the compressor, I would say you probably had low pressure being reported from the G65 refrigerant pressure sensor. This is supported by the much lower VAC and VDC that you got when compared to the values in the troubleshooting guide.

You might want to put a safety pin in the positve side of the wire to the clutch, and see if you still get the 9.5 volts to ground when there is a normal load on the circuit. (3.6 ohms is the proper expected reading for the coil.) I would do this before spending any money, if it were mine. Perhaps your fan control module has a different circuit than mine, and will always have 9.5 volts when unloaded? I have found that this is true; the only time a voltage check from the FCM to the compressor means anything, is when it has a 3 to 5 ohm load on it. Many newer FCMs have protective features that cut the power when the coil is shorted or opened.

If the loaded clutch circuit voltage is low, I would suspect that you either have an actual low refrigerant pressure condition, or a bad G65 sensor. The next move would be to check actual system pressures, and if they are good, verify the G65 is reporting the proper duty cycle for the pressure reading, or simply replace it.

I am writing this rather hurriedly. I will review it when I get a chance, to see if it still makes sense.

Dan

Last edited by DanG144; July 30th, 2015 at 04:22.
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Old April 29th, 2009, 14:58   #6
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I just easily turned my compressor by hand. It did not spin - it required constant force applied to keep it moving - but it turned with very little force.
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Old April 29th, 2009, 16:47   #7
WestMass
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Very interesting Dan. I will check the voltage to the compressor again in the morning to see if there is any difference when the harness is connected to the unit.

After feeling how easily the clutch plate spins, I checked the compressor on my sonís old Volvo sedan. It seemed to offer more resistance than mine.

Iíve ordered a fan control module, if for no other reason than the fans never came on during the 90 degree weather weíve had the past few days. It should arrive Monday. Once I install it Iíll post the results.

Thanks again!
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Old April 30th, 2009, 08:33   #8
WestMass
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Default Getting closer..

Quote:
Originally Posted by DanG144
A bad connection in the FCM, which is normally providing power to the clutch, could be the sole problem - when unloaded (as when measuring the output voltage at the compressor) the voltage would be 9.5, but it might drop when a normal load is placed on it.
Dan, the FCM is looking more likely the culprit. I checked the voltage on the compressor side of the connector to see if the 9.5 volts I found on the harness side with the connector unplugged was present under load - it was not. Zip Zero Nada. The load on the circuit caused the voltage to drop to zero. I did check for continuity across the plug, and it is fine. I'm REALLY hoping a FCM will get me going in the right direction. After it's installed, I'll see if the fans and compressor start. If they do and I still don't have cold air, I'll recheck the output from G65 to see if there is any difference with the compressor running. If there is no difference in the output from G65, should I head down to the local parts store for a container of R134 with a reuseable guage?

While I'm waiting for the FCM, I can get to work figuring out why the transmission started shifting hard yesterday.. when it rains...

Last edited by WestMass; April 30th, 2009 at 08:45.
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Old April 30th, 2009, 09:46   #9
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Until I saw the low AC and DC voltages you reported from G65 refrigerant pressure sensor, I too felt that it was most likely the FCM, as you quoted in the post above.

After I saw the low output from the G65, it made me start wondering if it was an opposite sort of problem, if your FCM would always put out 9.5 volts when it was unloaded. That perhaps it simply increased the resistance in the current path (instead of opening the current path) to the clutch when it wanted to turn off the clutch; this would limit current flow and shut off the clutch, but would show up as 9.5 volts when unloaded.

The internal circuits of the FCM likely change from time to time. As long as the functionality is the same, they will make changes to improve reliability and reduce cost.

One way to tell would be to put the voltmeter back on the clutch connector with it unplugged, and see the 9.5 volts DC, then unplug your G65 and see what the voltage does. Mine goes to 0.0 vdc out to the clutch when I do this. I did not have the ability to simulate lower than normal pressures when I was writing the troubleshooting guide; it was either normal, unplugged, or higher than normal pressures.

I can see that I will have to modify the guide, based on your experiences. I really appreciate all of the detailed work you have done and reported.

It looks as if I will have to make a duty cycle signal generator, in order to really nail this down.
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Old April 30th, 2009, 10:13   #10
WestMass
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Quote:
Originally Posted by DanG144
Until I saw the low AC and DC voltages you reported from G65 refrigerant pressure sensor, I too felt that it was most likely the FCM, as you quoted in the post above.

I can see that I will have to modify the guide, based on your experiences. I really appreciate all of the detailed work you have done and reported.

It looks as if I will have to make a duty cycle signal generator, in order to really nail this down.
Before you make any modifications to your guide based on my readings -especially the output from G65- let me get everything resolved. Then I can go back and take measurements after everything is working right to confirm what I have reported so far. I'm concerned about my analog multimeter's ability to accurately read the output from G65.
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Old April 30th, 2009, 11:40   #11
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I was going to wait, possibly until after the June 5,6 Asheville GTG, before I made the next revision.

I just wanted you to know that your information was valuable to us, and that I did not intend to miss any lessons learned. I am keeping notes to follow up on.

Do your fans ALWAYS come on when fuse 16 is pulled? Or do you need to have the AC on, with a fan speed selected? This issue was in my list to follow up on, but I have not gotten to it yet.
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Old May 8th, 2009, 13:58   #12
WestMass
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Default Getting closer

Hello DanG144, time for an update.

I installed a new fan control module, but it did not solve the problem. The fans did not work, and the clutch didn't engage on the compressor. I went back over your posts and guides and decided it was time to try some R134a in the system to see if there was any pressure. Bingo. As soon as I put a can in, the fans turned on and the clutch engaged. I'm in business, or so I thought. Cool air came from the vents in the cabin, but it wasn't nearly as cold as it should be. After turning off the engine, I could hear a very faint hiss from the front of the car, and after removing the bumper and grille, I found a small leak in the condenser. I've ordered a new one along with a drier, and hope to have it installed sometime next week. Once I do, I'll put in another can of R134a and see if it holds pressure. If it does, then I'll take it to a local AC shop and have them evacuate the system and put in the correct amount of oil and freon.

It seems strange to me that VW designed the AC circuit in such a way that the radiator fans are rendered inoperable when there is no pressure in the AC lines. This might be worth mentioning when you update your fan and AC troubleshooting guides. I was also sidetracked when the voltage at the compressor plug harness showed the correct 9.5 volts when unplugged, but the compressor clutch didn't engage when the harness was connected. Using your safety pin trick thru the hot side wire to measure LOADED voltage at the harness confirmed no voltage under load, and saved me from purchasing a new compressor. Zero voltage under load seemed to point back to the FCM being faulty, but in fact my old FCM is fine. I switched it with the new one and it worked like new while I still had pressure in the AC lines.

Once I get the new condenser and drier installed and everything is working, (hopefully that's all that's needed!) I'll check G65 readings and see if my analog meter was correct when I had such low values. If you or anyone else has any suggestions to make the installation of the condenser go smoothly, I'd appreciate hearing it.

Thanks again Dan

Al
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Old May 8th, 2009, 16:55   #13
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The amount of air allowed to flow through the drier is supposed to be critical. Take care to put the drier on just before you evacuate it.

Why not evacuate it yourself? You can rent the vacuum pump from Autozone or Advance auto, or buy one for $60-70 at Harbour freight.

Draw the vacuum to greater than 26" Hg then pump for about 45 minutes, (I don't have my manual, so someone chime in here), Then add the proper weight of R143a, (again someon chime in here), you also need to add the proper weight of PAG oil. (and here)

If I was not doing it myself, I would be tempted to let the AC service folks put on the drier, evacuate and fill it -even though it may cost a bit more to pay them for the labor and part. You could at least check the cost both ways before making your decision.

The blanks can be filled in from section 87 of the Bentley manual - but mine is not available to me.

I was sorry to hear that my efforts at a trouble shooting guide caused you to buy a needless part. The whole goal of the guide is to prevent wasting money.

I am not going to be able to make the changes for at least 10 days. But I will get to them.

I will change it so that no decision is made until after you have measured the voltage to the clutch under load.

And your post fill readings on the G65 will be very important to the effort.
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Old May 21st, 2009, 11:54   #14
WestMass
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Thumbs up Fixed!

Iím up and running. Replacing the condenser and drier went without a hitch. After installing it, I took it to a local shop and had them evacuate the system, charge it with the correct amounts of R134a and PAG oil and check for leaks. A week has gone by, and it appears the condenser was the only leak in the system.

I measured the output from the G65 pressure sensor today. With the harness plug connected and the white wire safety pinned, My analog meter registered 3.4 vdc with the engine running and the A/C off. With the engine running and A/C compressor engaged, I got 5.2 vdc. Outside temperature is about 80 degrees F. Curiously, my needle moved very slightly to the left (negative) while trying to measure ac voltage, the same distance no matter what ac voltage range the meter was in, both with the A/C running and not. Oddly, with no R134a (pressure) in the system before I replaced the condenser, I got readings of 1.5 vac and .64 vdc. This must be because of the square wave output of G65 as stated in the Bentley manual.


Quote:
Originally Posted by DanG144
I was sorry to hear that my efforts at a trouble shooting guide caused you to buy a needless part. The whole goal of the guide is to prevent wasting money.

If I had paid closer attention to your posts, I would have figured out that I didnít have any refrigerant in the system. I incorrectly concluded that the FCM module was faulty primarily because the voltage to the compressor dropped to zero under load, and the fans didnít come on when the outside temperature was 90 degrees. As luck would have it, the fan control module I purchased was faulty. Even though it worked after the condenser was replaced and the system recharged, there was a 2 amp current draw through it with the ignition off. This resulted in a dead battery in my driveway a couple days after the new FCM was installed, and another round of troubleshooting to figure out the problem. I found the current draw by pulling the fuses in the cabin one by one, and lo and behold fuse S16 showed the current. I pulled the new FCM out and replaced it with my old one, and everything is working fine. I returned the faulty FCM and got a full refund.

In review, here are a couple things I learned that may help others trying to figure out their own A/C and radiator fan issues:
  • The radiator fans will not run if there is low or no pressure in the A/C system, even if the outside temperature is very warm. As I said in an earlier post, it seems odd to me that VW would design this so that the fans are disabled if there is no pressure in the air conditioning lines. Never the less this seems to be the case; my fans did not turn on even when the temperature was 90 degrees F.
  • Be sure to measure LOADED voltage to the A/C compressor, in other words with the harness plugged into the compressor. If you measure voltage with the plug disconnected, it may show the specified 9.5vdc, which might lead you to believe you have a bad compressor. The voltage will correctly show zero when the harness is plugged into the compressor if there is no refrigerant pressure in the lines.
  • If you donít have a gauge to measure the pressure in your A/C system, you can check it by measuring the dc output of the white wire at the pressure sensor G65. Without refrigerant in my system, I had a reading of .64 volts dc. My pressurized system now reads 5.2 volts dc with the A/C on, 3.4vdc with the engine running and A/C off.
Thank you again DanG144 for your expertise helping me diagnose this. Have a cool summer!

Al
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Old May 21st, 2009, 12:05   #15
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I hope to revise the troubleshooting guide, based on your input, by Monday evening 5/25/2009, and send it to you for review.

Thanks for the follow-up information.

Dan
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