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A/C and both fans off

Tiny
RASCHKA
  • MEMBER
  • 2005 AUDI TT
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
Drove to work with everything operating fine. Started car after work and noticed A/C blowing hot air. Also noted that fan was off when A/C is turned on from head unit. Performed detailed inspection of the fuse box on top of battery. All fuses, wires, and contacts are perfect. Checked all bus fuses next to driver side area. All are present, have power from both sides, and are with the correct ratings. Performed voltage dropped test from battery to all terminals leading to fan control module up to the coolant thermo switch. Switch was placed in hot water and was able to hear click and verified continuity. Power has no resistance and voltages are exact. Fans were tested individually from direct battery power and were able to turn and spin. The loss of A/C and fans feel like a "switch just suddenly turned everything off". The A/C was cold when in use, usually set to 70-72 for comfort. Refrigerant should not be low but no tool to check. Vehicle has three error codes when using Foxwell 510 code reader with VAG-COM software installed. Airbag igniter for side passenger seat N200 (01218), problem with G113/V70 air flow flap sporadic - open/short circuit to positive code (00604), and a glitch when the doors open, the windows should drop slightly and the interior light should come on. Drivers side more reliable but the passenger side's window most always "up" when the door is open and interior light is off. Error stated in four parts. Alarm at door contact switch passenger side (01572)+ Alarm at terminal 15 (01374)+ signal wire for interior monitoring sporadic: Open circuit (01616)+ passenger door sporadic: Does not unlock (01560). Important thing to note. Ross-Tech offers good information about problems when installing or using aftermarket radios. Vehicle does have one previously installed when I bought the car used. I do not know if the connections were done correctly. It is possible the radio system could be creating problems shorting out the door contacts and the A/C fan circuit. I am losing "connection" after jumping power from the red wire to both red/white (low fan) and when testing red/yellow (high fan) at the thermo switch. I feel those connections either forward to the fan control module or the ECM. Except for those DTC errors noted, everything else is checking out to be perfect. I could use help with this diagnosis since I have never owned a OBDII car. Now I must learn both this system and the VAG-COM software layer to effectively determine problems along with their solutions. I do have pictures available upon request taken during the troubleshooting process to assist with this request for help. Thanks!
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Friday, October 6th, 2017 AT 8:45 AM

7 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,451 POSTS
The first thing I would check is the actual charge in the AC system. Low 134A will trip the pressure switch off and shut down the system.

As for the fans. They are designed to come on in stages as the engine gets warm. As the engine temperature hits the first fan on temperature it will turn on one fan at low speed, then as the temperature increases it turns that fan motor to high speed and if it gets even higher it turns on the second fan at high speed.

When you turn on the AC, if the system is charged and working the control head will turn on one of the fans to move air over the condenser and allow the system to dissipate the heat. In your case the fans all checked out and the most likely cause for poor AC is a low charge in the system. A quick way to tell would be to look at the AC compressor, Is it coming on when you turn on the AC? As for it not being low, it only takes one bad o-ring to dump the charge in a matter of minutes. On a twelve year old car, that would not be unusual.
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Monday, October 9th, 2017 AT 4:36 AM
Tiny
RASCHKA
  • MEMBER
  • 4 POSTS
Thank you Steve for responding to my online request for help. The A/C clutch does not spin at all when the A/C head is switched on. I did swap the high pressure switch with a new part just to see if the fans could be triggered but there was no change so I replaced the NAPA part with my factory original. I did the same with the coolant thermo switch. They both clicked close to the same amount of time after being dipped in hot water allowing continuity to be achieved using my tester. I do understand there is a difference between a standard wire providing voltage and one providing signal voltage. What I do not understand is how both fans are "shut off" to protect the car from damage just because the A/C system may require service. I feel that there is no signal reaching back either from a control module (J293) or the ECM. I was warned from a article about testing voltage to the A/C clutch as I could damage a circuit if applying voltage incorrectly so I dismissed that test completely. Just a note, there was no squealing or grinding of bearings of any kind before the A/C stopped suddenly. That entire system seems to be "shut down" due to loss of signal to be controlled. More research online helped to point out how information is communicated using both the K Line and also the CAN-BUS system. I don't have specific information to test these lines with or without a tool like the Pico Scope. I could be wrong with my diagnosis but after closely reading the error codes found using my Foxwell 510 code reader, there appears to be linkage to Terminal 15 having the "open/short" to positive. I do have the Bentley service manual in the event you require a specific wiring diagram.
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Monday, October 9th, 2017 AT 8:15 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,451 POSTS
Okay, so your fans do not come on at all even setting still and the engine gets hot?
They do not turn on to cool the engine until the coolant hits around 230 degrees.
At that point one will turn on, if the temperature keeps rising the second fan turns on.

Only one fan will turn on with the AC working. If the clutch is not engaging you have a low charge or a broken wire in the AC system. The fan will not come on in that case.
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Monday, October 9th, 2017 AT 9:39 AM
Tiny
RASCHKA
  • MEMBER
  • 4 POSTS
Thank you once again for replying back to this post Steve. I understand all the information you stated to me in regards to how the system is supposed to work but I'm more focused on the exact problem. There is no signal going back to the (J293) Fan Control Module to turn "ON" the fans. We know that direct power makes the fan spin but if they don't come on at all then there is something wrong with either a connection, wiring, or signal from the ECU or (J293) Fan Control Module. I did not see any other additional devices attached to this specific wiring diagram except for the Mega fuse and the standard Bus fuses. All those are correct and all voltage drop tests show continuity with no ground problems or electrical drains. I strongly believe the A/C system will work as intended once the fan issue is resolved. I also understand that the simple low fan circuit is partly controlled by use of a resistor within the fan motor. That resistor can burn out easily over time allowing only the High Fan ciruit to be enabled. The High Fan circuit should only come on after reaching the much higher temperature once triggered. However, if the fan is not coming on at the desired temperature, then there is no signal or voltage to start this process. I don't like to assume anything but it appears that the (J293) Fan Control Module is faulty although it's been replaced with a brand new part. I will have no choice but to buy another and reinstall to see if any fan speed actually turns on (High or Low). If they do, then most likely the Low Speed Fan's resistor is faulty too only allowing the High Fan circuit to run correctly. Once those issues are resolved, either the A/C will work correctly or there will be another problem to deal with respectively.
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Wednesday, October 11th, 2017 AT 4:30 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,451 POSTS
The AC system is what turns ON the fans not the other way around. Unless the compressor turns on there is no signal from the controller to turn on the fan. You have to test the system to see if it even has any 134A charge in it. No charge means no power through the system and no fan with the AC on.

You still have not said if the fans come on when the engine gets hot. If they do then the system is working properly and the issue is in the lack of AC operation.
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Thursday, October 12th, 2017 AT 1:58 AM
Tiny
RASCHKA
  • MEMBER
  • 4 POSTS
My apologies for the late reply Steve. A change in schedule prevented my more timely responses. The (J293) Fan Control Module turned out to be a faulty part even thought it was purchased brand new. So in theory, my thoughts were correct. The fans did come on but only at high temperature so the internal resistors were burned out possibly by the spike in power once the fan control module failed. Installed two new fans and the complete fan operation is now back in order working correctly. It's quite obvious with this vehicle that the (J293) Fan Control Module is responsible for the communication between the A/C system and fan control operation. The A/C clutch still does not turn on or spin but everything else is working fine. So now my attention has shifted to this question. How do you test the A/C clutch ring? Audi informed me that the clutch is serviceable on my vehicle and if I have no leaks in the system (which I do not and is standing at 650gr of charge) it is not necessary to remove or replace the compressor. Is there a method to troubleshoot this clutch ring to know if it's faulty? Your help in answering this question will be greatly appreciated.
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Tuesday, October 31st, 2017 AT 11:30 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,451 POSTS
The clutch is a simple wire wound electromagnet. One end of the wire is grounded through the Brown wire w/black stripe which also grounds the cooling fans at a common ground point near the battery tray.
The other wire, Green w/black stripe provides power. If the ground is good, applying 12 volts to the Green w/black wire will engage the AC clutch.
There could be a bad connection or the coil could be faulty or even just something as simple as the clutch air gap being excessive can all cause it not to engage.
It is fed the control voltage through the fan control module you replaced and tells one fan to turn on at the same time the clutch is engaged.
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Tuesday, October 31st, 2017 AT 6:01 PM

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