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Hi all,

My ac worked perfectly fine, and today I left my sister in the car idling with ac on for about 20 min. When I approached my jetta I smelled something like a burning tire. When I got in the car, ac was not blowing cold anymore. Water temp was at 190 F, however when I parked it in my garage, and turned the engine off, radiator fan was still running. Ac compressor was not spinning. Ac light on the switch is ON when the button is pressed. Where should I start with this one? Thank you in advance!
 

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Does turning the fan speed to the different positions make any difference? This could be a bad clutch or resistor pack. Maybe the belt is gone?
 

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Discussion Starter #3
resistors - I think resistors are OK since fan operates in all settings 1-4
belt - belt is OK still spinning
clutch- maybe, but can it fail suddenly to the point that it is not turning at all ( I think it would first start to slip slowly before completely not engaging.
 

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The clutches used are engaged electrically, so they would not wear slowly and slip like a regular clutch. Also, other things could be wrong. The air conditioning system has pressure switches that will not allow the compressor to start, for example, if the system refrigerant charge gets too low, the pressure switch on the suction side will not allow the compressor to start. Also, check fuses.
 

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The clutches used are engaged electrically, so they would not wear slowly and slip like a regular clutch. Also, other things could be wrong. The air conditioning system has pressure switches that will not allow the compressor to start, for example, if the system refrigerant charge gets too low, the pressure switch on the suction side will not allow the compressor to start. Also, check fuses.
I understand that, but what confuses me is something smelled like a burning rubber when ac quit working. Not like an electrical burning smell, it was true smell of burning rubber.
 

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I would start with the basics, can you see the compressor clutch engage?

***Don't get caught in the belt systems.***

Turn the AC off, start the car, and have someone activate the AC while you are watching the AC pulley. You should hear an audible noise when the clutch changes and you should see the inner diameter start to rotate.
 

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burning belt /ac compressor pulley stuck

after some research I concluded that the only thing that could have happened in this case is that the pulley on the ac compressor for some reason froze causing belt to continue spinning. But what is confusing is that ac compressor pulley is spinning normally now but clutch is not engaging. Why? Is this some type of fail safe mode for ac compressor? If ac compressor is seized, I believe the pulley would be frozen as well.

Is there a quick way to check cooling fan module, because I see some connection with the ac clutch wiring? When ac is on, are both fans supposed to be working or?
 

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Not sure what the "permissives are" (conditions that must be met before an order will be given) for the AC clutch in your TDI. However, applying the KISS method, start with the basics and work back towards the complex.

With the engine "secured" and the key out of the ignition, disconnect the electrical plug to the AC clutch and take an ohmic reading. You should have a very low ohmic reading. I don't have the TP in front of me, but a coil designed to cause a mechanical movement of this size should be well under 25-ohms. Using R=E/I, and assuming a 10-amp circuit draw, you should see an ohmic value in the neighborhood of 1 to 2 ohms. If you show a very high reading or an open circuit, you simply have an AC clutch that is burnt out and requires renewal.

If there are (2) wires on the harness going down to the compressor clutch, then check to ensure the AC clutch coil is not grounded to the case. Take an ohm reading from the compressor case back to one of the leads, then repeat from the other lead to the compressor case. Both readings should be very high and ideally read an open circuit, greater than 1M ohm.

I am assuming that you have checked all of the associated fuses. Fuses don't always blow or fail in such a way that they are 'visibly' blown. I would check the associated fuses with an ohm meter.

As for the permissives, I would get a circuit diagram in front of you and start walking the circuit. Most permissives will stand out (interrupts the main circuit with decommissioning ability) or there will be a note if they are controlled in the higher order logic of a control module. The (3) most common HVAC permissives are, and they depend on the application, suction-side low pressure (loss of charge), discharge-side high pressure (lack of heat transfer across the condenser, an overcharge, or a clogged TXV or drier...system obstruction), and low oil level/pressure (not very common on automotive applications).

High side obstructions don't cause a full system lock out, unless the circuit is designed to latch. High side pressure shut downs cause short cycling, as the pressure will bleed back down thru the system and then the compressor will make another attempt, but will run for a very short duration.

Automotive applications do include a "wide open throttle" circuit on the AC system, which forces a decommissioning of the compressor clutch to increase the available horsepower at the tires when you put the pedal to the floor. The AC compressor clutch will remain decommissioned until you reduce the throttle.
 

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Let me know what you figure out...same thing just happened to me today...A/C turned on and was cooling the car, then I would assume the compressor locked up and the serp. belt is spinning around a stopped pulley. when I saw smokew I turned off the A/C. terrible way to be stranded on the road! Why would the pulley/compressor be locked?
 

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Let me know what you figure out...same thing just happened to me today...A/C turned on and was cooling the car, then I would assume the compressor locked up and the serp. belt is spinning around a stopped pulley. when I saw smokew I turned off the A/C. terrible way to be stranded on the road! Why would the pulley/compressor be locked?
disconnect ac compressor connector (green and brown wires) measure resistance of the clutch coil and see what you get. Mine is open now so I have to order new one, plus I will also need FCM.

Try this also: ignition key ON, engine off, ac on, blower setting to 1, then see if both fans are spinning at low speeds under the hood. Both fans should work, if yours do spin then you are for the most part ok. if not then you will have to troubleshoot fan motors, fcm, fan thermo switch and related wiring.
 
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