Check your radiator/condenser fan operation NOW

Checked the resistance on the fan. It's shot. I'm going to look at the brushes on Sunday. Now, could it also potentially be a problem with the compressor? I imagine that it could also be a problem.

It could be the clutch.

But you have some control failure as well.

Please unplug your AC high pressure sensor and see if the fans still come on when you turn the key on. This is located near where the high pressure gauge connection is.

Dan

Ok, had mine working earlier this year. I just checked them today and niether fan runs in slow speed but the clutch engages a/c works, the high speed fan will kick on then off? If I jump the thermal sitch I get both slow (pins 1-2)and high (pins 2-3) speed operation.

From the guide it seems to me it must be the radiator thermal switch? Does that make sense? Anyone know the resistance? Can I check it with my Vag Com?

It would not be the thermoswitch. It would be the fcm.
Try the engine module output tests, see if it has a fan check.
This fan check would also try to run the slow speed fans via the fcm. If this does not work that would nail the fcm slow speed fan relay as the culprit.

I jumped pines 1 and 2 on the thermo switch. It DOES have 13 volts, but the fans don't turn on, and i hear a click and the "dinger" on the inside of the car goes off (like if you have the lights on and key out) and the abs and air bag light turn on (but dimmly). Whats up with that?? The AC also doesn't work, and the AC pushbutton is dimmly lite like the abs and srs light. When i cycle the key is resets the abs and srs light, but the AC light still goes on. When the car sits in traffic when its warm out i go to shutt off the car, it won't turn off and the abs and srs light are on then as well and i have to pop the clutch to shut off the car. I just checked pins 1-3 on the driver side fan with the key off and pins 1 and 2 jumped on the thermoswitch. Pins 1-3 at the fan all have 13 volts, even though i assume i should be a ground and not 13 volts like it is, lol. So its the FCM I assume now?

It sounds as if you may have a wiring problem and you may have an FCM problem.

You very well may also have a fan problem or two.

Jumping pins 1-2 of the thermoswitch should start the fans on slow speed even without the FCM in the car.

It sounds as if you may have a bad ground on the wiring harnes grounds. all the grounds from the FCM, G65 high pressure sensor, the fans, and the AC clutch come together at conection 193 (in the fan wiring harness) then one wire goes to ground 12 (engine compartment left) 4.0 mm brown and black wire.

I would unplug the FCM (both the T4 and T14) and see what symptoms remain. Retest your fans from the thermoswitch jumping pins 1, 2.

Test the fans directly - put 12 v across their pigtails using the directions in the first post.

Let us know what you find out.

Any chance you could point me in the direction of connection 193? Not sure if i have a good diagram here. I did jump the fans using the battery, they both work on high and low speeds. I have yet to unplug the FCM. I'll keep posted.

I would have to trace the ground wire from the fan back. It almost has to be right at the battery, underneath it probably. The ground should also be very close to the FCM. You will have to open up the wiring harness protective cover, tape or heat shrink.

I have no pictures or explicit information on connection 193 or ground 12 - I gave you the words out of the Bentley in the post above. Please take photos for the rest of us if possible.

well, chalk up another tdi with a/c problems..

last summer, A/C worked 100% ICE COLD.

i go to turn the a/c on the other day and nothing.


today i started to trouble shoot, key on with the a/c button on, both fans kick on.. i start the car, fans are on but the compressor doesn't engage.. i tested voltage with a multimeter at the plug and its getting a consitant 5.0 with just the key on..

i also tried jumping the plug by running 12v from another battery directly to the plug while the car running.
also i checked the fuses on the battery and in the car and all were good.

all wires look to be good running to the fcm. i'm stumped

also, the system is full of refrigereant.

DanG144- any hints?

If you jumped 12 v directly to the clutch connections ( One positive one negative) and it did not engage the clutch, then you have a clutch issue.

Check the resistance of the clutch winding, going from memory (check me in post #1 docs) the resistance is about 4 ohms.

To test the voltage out of the FCM to the clutch, you must put a load on it. A light bulb, a resistor, or the clutch coil. With a load on it, it will go to about zero when it is off and about 9 volts or more when it is on. When the key is on, a cabin fan is selected to on, and the AC button is pushed (and you are not in defrost) you should get 9 volts or more from the FCM.

DanG144 said:

If you jumped 12 v directly to the clutch connections ( One positive one negative) and it did not engage the clutch, then you have a clutch issue.

Check the resistance of the clutch winding, going from memory (check me in post #1 docs) the resistance is about 4 ohms.

To test the voltage out of the FCM to the clutch, you must put a load on it. A light bulb, a resistor, or the clutch coil. With a load on it, it will go to about zero when it is off and about 9 volts or more when it is on. When the key is on, a cabin fan is selected to on, and the AC button is pushed (and you are not in defrost) you should get 9 volts or more from the FCM.

Click to expand...

ok well i also tried checking resiustance but i don't think i did it right, mind explaing how to check resistance on that?


also, can you explain how to test the fcm to the clutch? what do you meran by putting a load on it? im 1/2 retarded when it comes to electrical LOL

thanks for the help so far!

also, i tried removibng the clutch, i got the 14mm nut off, circlip off but the pulley would just NOT come off!

Well yesterday I noticed that the AC was not performing as well as it did, so I checked the fans with the car off and the AC on, and the fans were spinning slowly. Started the car, with the AC on, and the AC clutch engaged and the fan immediately went to high speed. Its about 35c here today. I thought this was odd, so I turned the car off and checked the fans again and lone behold, the driver's side fan would not spin! I assisted it gently and it started to spin slowly as it should so I guess the driver's side fan is the culprit.

I also noticed while driving I could notice the ac compressor cycling on/off, due to the power loss for a split second. I am assuming this is not normal either?

SheeB said:

Well yesterday I noticed that the AC was not performing as well as it did, so I checked the fans with the car off and the AC on, and the fans were spinning slowly. Started the car, with the AC on, and the AC clutch engaged and the fan immediately went to high speed. Its about 35c here today. I thought this was odd, so I turned the car off and checked the fans again and lone behold, the driver's side fan would not spin! I assisted it gently and it started to spin slowly as it should so I guess the driver's side fan is the culprit.

I also noticed while driving I could notice the ac compressor cycling on/off, due to the power loss for a split second. I am assuming this is not normal either?

Click to expand...

You are correct. The clutch should not cycle on the A4 cars at all during normal operation.

It sounds as if you may be reaching high pressure conditions due to lack of fans to provide cooling, which will turn off the clutch on the AC compressor.

Thanks for the quick reply DanG144

So now that I drove the car home from work and the motor is hot, outside temps are real hot for this time of year for us, is this why the fans immediately went to high speed?

Time to see where everyone is getting the replacement fans from, and see if there is a DIY to change it out. I need my AC!

Spray a waterhose on your condenser coil. This will reduce the temperature, and thus the actual pressure inside the system, to normal.

This should allow your fans to be off rather than in high speed (as they try to run in slow, but I understand your slow speed fans are failed.) As long as you spray the water, the AC compressor should run, if you stop spraying the water within 2 minutes it will probably be at high pressure again. If this is what happens, then repairing or replacing the slow speed fans should solve all of your problems.

If it does not work properly with the water spray you might have a bad high pressure sensor.

If you unplug your high pressure sensor and your fans turn off, you know that is the source of the fast speed fan signal (as opposed as it being from your ECU or radiator thermoswitch.)

Wow, super good info indeed! I will do the hose test and see what happens. My drivers side fan seem to be the one that does not want to consistently have low speed.

DanG144 said:

I would have to trace the ground wire from the fan back. It almost has to be right at the battery, underneath it probably. The ground should also be very close to the FCM. You will have to open up the wiring harness protective cover, tape or heat shrink.

I have no pictures or explicit information on connection 193 or ground 12 - I gave you the words out of the Bentley in the post above. Please take photos for the rest of us if possible.

Click to expand...

I will certainly take pics, my wife has the car today, so I'll get to it when i have the car back

DanG144 said:

Spray a waterhose on your condenser coil. This will reduce the temperature, and thus the actual pressure inside the system, to normal.

This should allow your fans to be off rather than in high speed (as they try to run in slow, but I understand your slow speed fans are failed.) As long as you spray the water, the AC compressor should run, if you stop spraying the water within 2 minutes it will probably be at high pressure again. If this is what happens, then repairing or replacing the slow speed fans should solve all of your problems.

If it does not work properly with the water spray you might have a bad high pressure sensor.

If you unplug your high pressure sensor and your fans turn off, you know that is the source of the fast speed fan signal (as opposed as it being from your ECU or radiator thermoswitch.)

Click to expand...

Ok, sprayed for a good 5 minutes the lower portion of the front of the radiator with the car idling, the fans never went to slow speed or no speed, stayed at high speed.

Unplugged the high pressure switch, and had no fans with either the car idling or with it off (but AC button always depressed) and the AC clutch would not engage (when idling)

These are the symptoms of a failed high pressure sensor.

Plug everything back in, and watch your fans the first thing in the morning. If they go to fast as soon as you turn on the key on a cold soaked car, then it is not possible for the pressure to be too high (unless someone added way too much refrigerant.)

You can replace the HP sensor without losing your AC charge. It is mounted on a schrader valve (like a tire valve stem). Just unscrew the old one, install the new one.

Check your fans out as well. See if they will run in slow from the radiator thermoswitch with the High pressure sensor unplugged electrically.

It seems that some hp sensors fail high after being subjected to high pressures. As if they stick. The usual cause of high pressure is failed fans.

Of course, some HP sensors just fail.

Hmm, well I know for sure I have a failing/failed large(driver's) fan which started squealing today randomly. This is what alerted me to something amiss with the ac system.

The fan could have been malfunctioning since last summer, but I did not use the AC much last summer as we got so much rain. I will definitely replace the fan (if not both if I can source out one of the Dorman units locally (in Canada). I will not use the AC till I do this and the high pressure switch. I have not topped up the refrigerant myself, but I have only owned the car for just over 2 years myself.

Is the high pressure switch this? http://www.worldimpex.com/parts/german-ac-pressure-switch_908640.html

Thanks for all the help with the troubleshooting. I will try the AC with a cold motor in the morning and see if the fans still go to high speed.

I wonder if I should check (if it can be done by mel) to verify roughly how much refrigerant is in the system? I think I may have read something in your FAQ about this.

TheKid7 said:

I plan to not further investigate my "similar problem" at this time. I will just live with it for now. The problem seems to bother me a lot less since I have decided to just live with it for now.

Every time the engine warms up, the problem seems to go away.

Thank you for your input.

Click to expand...

I changed my mind about further investigations. This evening I made multiple visual observations of the belt tensioner and pulleys with and without the AC on. The pulsing/surging problem, which is only noticeable from inside the car, is still there and only when the AC is on.

Is it normal to have a "slight" vibration of the belt tensioner? I will try to quantify the tensioner vibration that I saw as (+/-) 1/16" (not measured). With the AC on, I am not sure if there was more tensioner vibration. If there was more vibration, it was barely noticeable over without the AC on.

Does anyone have any more ideas on what to check to aid in solving my problem?

Note: The surging/pulsing seems to be in about 5 second cycles and can usually be also sensed in the feel of the steering wheel. Once the engine rpm picks up above idle everything seems smooth. The problem is only noticeable at engine idle.

Thanks in Advance.

That is the right pressure sensor (even VW and Bentley call it a switch sometimes.)
There is no real way to check to see if you have a full charge at home - you have to weigh it. Pressure checks can tell you that you are not empty, that you have some liquid refrigerant left, but not how much; it may only be 1/10th of the original charge.

The only way to ensure a full charge is to remove the charge, do a leak check, evacuate the system and do a recharge with known weight/mass.

You may not have a charge mass problem at all. No indications of that.

Dan

SheeB said:

Hmm, well I know for sure I have a failing/failed large(driver's) fan which started squealing today randomly. This is what alerted me to something amiss with the ac system.

The fan could have been malfunctioning since last summer, but I did not use the AC much last summer as we got so much rain. I will definitely replace the fan (if not both if I can source out one of the Dorman units locally (in Canada). I will not use the AC till I do this and the high pressure switch. I have not topped up the refrigerant myself, but I have only owned the car for just over 2 years myself.

Is the high pressure switch this? http://www.worldimpex.com/parts/german-ac-pressure-switch_908640.html

Thanks for all the help with the troubleshooting. I will try the AC with a cold motor in the morning and see if the fans still go to high speed.

I wonder if I should check (if it can be done by mel) to verify roughly how much refrigerant is in the system? I think I may have read something in your FAQ about this.

Click to expand...

TheKid7 said:

I changed my mind about further investigations. This evening I made multiple visual observations of the belt tensioner and pulleys with and without the AC on. The pulsing/surging problem, which is only noticeable from inside the car, is still there and only when the AC is on.

Is it normal to have a "slight" vibration of the belt tensioner? I will try to quantify the tensioner vibration that I saw as (+/-) 1/16" (not measured). With the AC on, I am not sure if there was more tensioner vibration. If there was more vibration, it was barely noticeable over without the AC on.

Does anyone have any more ideas on what to check to aid in solving my problem?

Note: The surging/pulsing seems to be in about 5 second cycles and can usually be also sensed in the feel of the steering wheel. Once the engine rpm picks up above idle everything seems smooth. The problem is only noticeable at engine idle.

Thanks in Advance.

Click to expand...

Have you checked your power steering system volume?

DanG144 said:

Have you checked your power steering system volume?

Click to expand...

The power steering fluid level is fine. It seems like the surging/pulsing can be sometimes mildly felt in the steering wheel.

Well I tried the AC on the cold motor this morning and the fans did run in slow mode when idling. I let it idle for a couple of minutes and they did not go to high speed? I drove to work with the AC off the whole way and while leaving the car idling, turned AC on and fans immediately went to high speed? Do you think the high pressure switch should be considered for replacement?

DanG144 said:

At 1500 rpm, blower speed to fast, max cooling. You should have about 200 psi on the high pressure side, and 17 psig on the low pressure side.

It can be dangerous to just add refrigerant to a system, without knowing how much is already in the system. An overcharge can take the compressor discharge side completely full of liquid (no gas space left) and cause pressures to skyrocket, popping safety valves, challenging control systems, and potentially breaking hoses, tubes and compressors.

High Kinetic Energy rotational disassembly of the compressor can be hazardous to your person. That is pentagon speak for blowing it up.

Click to expand...

How are you coming up with these readings? If you had 17 on the low side the evaporator would be a block of ice. Readings also depend on humidity, ambient temp etc.

SheeB said:

Well I tried the AC on the cold motor this morning and the fans did run in slow mode when idling. I let it idle for a couple of minutes and they did not go to high speed? I drove to work with the AC off the whole way and while leaving the car idling, turned AC on and fans immediately went to high speed? Do you think the high pressure switch should be considered for replacement?

Click to expand...

This is why you want to be thorough.
It seems the condenser did not get adequately cooled yesterday with the water spray.

I will try to get back to you tonight.

hevster1 said:

How are you coming up with these readings? If you had 17 on the low side the evaporator would be a block of ice. Readings also depend on humidity, ambient temp etc.

Click to expand...

hevster,
They came directly from the Bentley manual chart for normal operation.
I, personally usually see more like 25 psig on the low side on my own cars and up to 35 psig on others.

I have tried (not very successfully) to keep this thread on the electrical control side of things. So I gave a simplistic answer to a question that obviously came from a novice at AC work. Perhaps I should have ignored the question.

Knowledgeable folks know that the refrigerant cycle pressures and temperatures vary depending upon the conditions - and how they vary, and why they vary. I refuse to attempt to try to address these issues unless I am in a one on one situation. I simply am not up to the task via a written media.

Now if someone else would attempt a troubleshooting guideline thread on the mechanical side of things...

SheeB said:

Well I tried the AC on the cold motor this morning and the fans did run in slow mode when idling. I let it idle for a couple of minutes and they did not go to high speed? I drove to work with the AC off the whole way and while leaving the car idling, turned AC on and fans immediately went to high speed? Do you think the high pressure switch should be considered for replacement?

Click to expand...

So when refrigerant pressure was essentially guaranteed to be normal, due to being at ambient temperature, the HP sensor was putting out a pressure in the normal range, as indicated by the fan and clutch response, for at least two minutes at idle.

Normally one fan running in slow is enough to prevent reaching the high pressure clutch off condition.

I would want to check your hp sensor duty cycle output vs pressure at two points at least 100 psig apart before I suggested replacing it. Can you get a set of pressure gauges and a meter capable of measuring duty cycle? Find the table of pressures, temperatures and duty cycle in post #1 to know what your hp sensor output should be at a given pressure.

Can you put a thermometer in your center dash air outlet and check temperatures?

Since you know you have one bad fan, why don't you repair or replace it and see what that does? Is there much of a chance that both slow speed fans are failing intermittently? This would not be too uncommon, and could explain the issues you are seeing.

We really need to see the parameters to troubleshoot this. Sorry I do not have a magic bullet.

I personally do not have a set of pressure gauges or a duty cycle meter. Off the top of my head, I do not know anyone personally that would have this stuff to loan me either.

I ordered the replacement driver's side fan today, and will replace it hopefully this weekend.

I honestly do not recall the hearing the fans come on except when the AC was on, which seems odd to me compared to a gasser motor.