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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKV-A5 Golf/Jettas

VW MKV-A5 Golf/Jettas Discussions area for A5/MkV Jetta/Golf (2005/2006 PD and 2009 CR).

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Old July 8th, 2011, 21:48   #46
DanG144
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You can easily check it with an oscope. It is simply a pulse width modulated signal proportional to pressure. Just calculate the percentage of the time at high voltage, and compare the chart embedded in a pdf in post #1 here it is for mk IV, but I think the sensor is identical.

I think it is right hand side forward, near the radiator in the mk V.. In any case you can follow the high pressure line back from the TXV at the fire wall to the condenser, and find it.

It is more easily checked with VCDS, because you not only see the duty cycle in percent, but you also see the control current sent to the RCV.

You can also see the interlock status, and the status of the delay timer.
There is a circuit in the system that can cause a purposeful delay of up to 4 minutes. I do not know the conditions where this comes into play, but have never (yet) seen it be the cause of the delayed cooling.

In all the delayed cooling situations I have looked at, the RCV was getting full current, which should provide full cooling. But something was sticking, either the RCV, the piston, or the wobble plate.
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Old July 9th, 2011, 06:31   #47
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Quote:
Originally Posted by DanG144 View Post
You can easily check it with an oscope. It is simply a pulse width modulated signal proportional to pressure. Just calculate the percentage of the time at high voltage, and compare the chart embedded in a pdf in post #1 here it is for mk IV, but I think the sensor is identical.

I think it is right hand side forward, near the radiator in the mk V.. In any case you can follow the high pressure line back from the TXV at the fire wall to the condenser, and find it.

It is more easily checked with VCDS, because you not only see the duty cycle in percent, but you also see the control current sent to the RCV.

You can also see the interlock status, and the status of the delay timer.
There is a circuit in the system that can cause a purposeful delay of up to 4 minutes. I do not know the conditions where this comes into play, but have never (yet) seen it be the cause of the delayed cooling.

In all the delayed cooling situations I have looked at, the RCV was getting full current, which should provide full cooling. But something was sticking, either the RCV, the piston, or the wobble plate.
Full current to the compressor pretty much indicates a bad pump huh???
I wonder if an external, higher current, drive would pursuade it to start working. I believe I read 830ma to be full on? Compressor should look like 15-17 ohms then. However, I suspect it is PWM driven.
Perhaps "nudging" it with a couple of amps might get it loose. I would really like to see the internals of this compressor.

Geez, This car has been nothing but a money pit.
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Old July 9th, 2011, 14:52   #48
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It is a pwm signal.

You can put 12 volts to the RCV, and (at least when I did it) you get no more displacement than before. When I did it no harm came to the RCV or compressor. I did it only long enough to see that pressure did not rise any more with my power than with the ECU power - maybe two minutes.
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Old July 10th, 2011, 11:35   #49
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I just noticed one of the fans is not running. Should they both be on when the ac is on and engine is up to temp?
Could this be related to the compressor delay? I'm thinking the ecm may see the fan's open circuit and delay the compressor pwm drive.

Dan
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Old July 10th, 2011, 14:58   #50
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Both fans should run together at the same speed (or stopped) all the time. They will normally start about 20 to 60 seconds after your compressor starts pumping - they will not run (for AC reasons) unless your compressor is raising pressure.

The computers only monitor the output of the controller built into the large fan. It assumes both are running at the same speed.

The computer will monitor the high pressure side and cut back the displacement if it gets too high. If your fans don't run the temperature goes up and the pressure goes up. So a single fan can cut back the available cooling.

You need to fix the fan, but I doubt if it causes your delay.
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Old July 10th, 2011, 18:48   #51
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Thanks!
It sounds like you understand the system better than the dealer we have had dealings with.
I will fix or replace the fan and go from there.

Dan
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Old July 14th, 2011, 22:05   #52
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Default Backyard A/C 101

2006 Jetta TDI A/C system (05.5-09 at least)
If your A/C is intermittent or just stopped working check this out.

FYI VW has never been a great inventor of Air conditioning.
It should be simple turn on off like everyone else. But Noooo they need to make it better.

Here is the basics.
you will need a set of gauges, so if you have a harbor freight tools and $50. you can test your AC system.
  1. hook up the gauges to your system and see that you have Freon approx 70-85lbs static with the engine off.
  2. Turn on the engine and see if the pressure changes. Of course with the a/c turned on.
  3. You should read on the low side somewhere between 25-40lbs and the high side 150-250lbs. Depending on how hot it is and some other factors.
  4. The A/C compressor is does not have a clutch. VW thinks they have a better idea instead of doing what everybody else does that works just fine.
  5. This is a variable pressure system kind of like GM waffle plate compressor but much worse.
  6. Make sure both your fans are working even if intermittent.
  7. if one fan is working you probably need a fan.
  8. If it is cool enough out you can turn your thermostat to 80 and it should blow hot air. This will tell you if the thermostat is working.
If you have done steps 1-8 and your pressure does not change. Chances are you need a compressor. These are known for failure and are very hard to test since all goes through the Control module. What I did on mine is roll the dice and purchased a compressor on ebay. Probably Chinese but works better than the so called Quality Sanden I aggressively bowled to my trash can.

The old style Sanden compressors were bullet proof. But this variable pressure no matter what brand you purchase will have problems.

This is not a fool proof method of checking your system. If you have a fat wallet you can go to the dealer and probably pay up to 2g's to have them do it. You could get test equipment check circuits get all flustered trying all this stuff for a month scratching your head, reading, fighting it, trying to remove the actuator on the compressor, or just change the compressor which takes about an hour and 4 bills.

Why did I go with a cheap compressor? Because nobody has figured out how to make this system work. I am just buying time until the good compressors come down in price enough or someone like Everco has a solution compressor upgrade to the sticking piston in the variable pressure system.

Hope this helps.
Mike

Last edited by farnhamassoc; July 14th, 2011 at 22:11.
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Old July 15th, 2011, 03:34   #53
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Mike,
A couple of things.
If one fan ever turns by itself - your other fan is broken - they always should turn together. Is is wiring? Is it brushes?
The fans are controlled by refrigerant pressure- if it never gets high they will never be asked to turn on.
If the fans are broken, the refrigerant pressure will get too high and the compressor RCV will be turned down to lower the displacement and the pressure.

System pressure should initially be checked at ambient conditions. If your pressure and temperature match the R134a saturation table, then you have at least SOME liquid refrigerant in your system- but you cannot tell if it a one drop or 24 ounces. 68 F = 68 psig, 104 F = 132 psig.

You can borrow a VCDS system, use that and see what the control signals are doing. If your RCV (Refrigerant Control Valve) is getting full current of about .820 amps, and your pressure is low then you can be almost certain that the compressor is bad (sticky RCV, wobble plate, piston.)

When you replace your compressor, change out the TXV and filter-drier as well. Many people have used cheaper TXV's and they made howling noises as they throttled.

I hope the cheap compressor works well for you. Personally I would find the cheapest Sanden and use that.

If you are going to go cheap and gamble, why not remove the compressor, drain the oil, add two or three ounces of PAG 46 oil with ICE in it, and reinstall it?

Simply adding an ounce of PAG 46 oil with ICE in it has allowed one compressor to lose its delay.

Of course, it could quit working today.

Last edited by DanG144; July 15th, 2011 at 03:45.
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Old July 20th, 2011, 03:31   #54
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OK, I am having the same problem. 06 with 170k, just a normal AC system. Last yr I started having the delay when 1st starting the car, and taking 10 min to cool down. When you come to a stoplight, sometimes the car stays pumping cool air, other times it gets a bit warm.

I started the car yesterday after it sat all day at work. I turned the AC on and popped the hood. Only the large fan was spinning. I drove it home 35 miles and when I shut the car off I immediately checked the fans and only the larger on was spinning down.

On the drive home I called my dealer, which the service guy seems pretty sharp. He tells me the 2nd fan will only come on when requested by the ECU for when the large fan can't keep up. Said its not related to the AC at all. But, after reading thru this, I'm wondering if he is correct. I will say after the 1st 10 minutes, the car pumped out cool air and did so during stops. Driving well over 100 miles in 95° heat, I only had the AC fan at 2, and was very comfortable.

Anyway, dealer says I may be a tad low on Freon, and the HI/LO pressure switch may be a problem, as he has replaced many. What I have come to the conclusion is most dealers suc at troubleshooting, and would rather just start throwing parts at you....”Here is a fan. NO fix? Try a switch. Nothing?.... Here is a compressor. Still no?...... hmmmm, what else can I sell this guy?........ I don’t want this, which seems is the outcome when most go to the dealer with AC issues.

Is there a link or anything that someone can supply for me to check this fan? Is it hard to replace yourself? How much is the fan or is it normally repairable?
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Old July 20th, 2011, 04:29   #55
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On your car, both fans should always spin at the same speed. They are both driven by the same power supply, that is built into the back of the larger fan. Whatever power (pulse width modulation) that is sent to the large fans is simply wired to the small fan.

So your dealer is wrong about the fans. He may seem to be sharp.

From your description, fixing the small fan would help.

But would not fix your delay.

Putting VCDS on it for about 10 minutes would show exactly what was going on with the rest of the system.

Last edited by DanG144; July 20th, 2011 at 04:31.
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Old July 20th, 2011, 04:54   #56
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Quote:
Originally Posted by DanG144 View Post
On your car, both fans should always spin at the same speed. They are both driven by the same power supply, that is built into the back of the larger fan. Whatever power (pulse width modulation) that is sent to the large fans is simply wired to the small fan.

So your dealer is wrong about the fans. He may seem to be sharp.

From your description, fixing the small fan would help.

But would not fix your delay.

Putting VCDS on it for about 10 minutes would show exactly what was going on with the rest of the system.
Thnx for the reply. Is the smal fan normally repairable, or is it just replaceable?

Is the wiring easy to get to where I can check to see if teh small fan is getting power? How ard is it to remove the fan without a lift?
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Old July 20th, 2011, 05:10   #57
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I just got 2 new fans from Idparts online......gonna install on saturday....be nice to have a DIY somewhere!!!
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Old July 20th, 2011, 07:33   #58
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Had this problem on an 06 Jetta. Before you waste $$$$ on a fan, know that road sand/grit can work its way into the fan motor brushes and this can be fixed in very few minutes.

Remove the fans and work your way to taking the simple motor apart. Check for crud between the fan brushes and the rotating portion of the fan. The brushes are the grey graphite square things with springs. You will need to hold these spring loaded brushes back when you put the motor back together. Use a scotch pad to shine things up.

My cleaned out fan has lasted over 50,000 miles so far.

Also, all are correct when they say both fans should run at the same time. Furthermore, the loss of a fan can and will kill your compressor. If both fans are running, and you still have AC delay turn on issues, your compressor is shot. Been there, too.

Another note, if having your compressor replaced by a non-stealership, make sure you let them know that VW AC systems do NOT use pressure as an indication that the system is "full". A metered amount of oil and freon/whatever must be put in. Otherwise, you will way overcharge the system.

Also, just after my new compressor was installed, the clutch/pulley on the alternator went. The symptom was loud squealing whenever the AC was turned on. You can imagine how this symptom took us in the wrong direction. If you have high mileage, I suggest replacing the alternator clutch while the works are apart. I think it is a pretty cheap part.

I am still having a small problem with ice over on my new compressor. At the lowest fan speed traveling at night, the evaporator will freeze over the condensation into a block of ice, blocking all air flow. I have to shut the AC off and run the fan at full blast to melt it away. The stealerships have absolutely no idea how to fix this.

Last edited by john_tsouris@hotmail.com; July 21st, 2011 at 13:40.
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Old July 20th, 2011, 08:09   #59
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Quite often the small fan failing to run is due to stuck brushes. You can open the back of the fan, clean them, maybe scrape the brush holder with a knife to make it smooth so the brushes move freely in the holder.
It has been written up on the site.
You can inspect the wires and find the place to check for power - if you have a meter that can read duty cycle.
The wires are short and direct from the module on the back of the large fan, easy to inspect.
I think on the 06's you are best off to have it on jackstands with the belly pan off to remove and replace the fans. It is tighter than the mk IVs. You may be able to take it out the top - it might be worth a try. I think all you need is a torx 30 and the joints of a contortionist.
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Old July 20th, 2011, 08:15   #60
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The ice over may be due to a TXV problem. Look for a PM. Do you have a VCDS system? If so, or if you can get to one, we can find out why it is icing.

Dan
Quote:
Originally Posted by john_tsouris@hotmail.com View Post
Had this problem on an 06 Jetta. Before you waste $$$$ on a fan, know that road sand/grit can work its way into the fan motor brushes and this can be fixed in very few minutes.

Remove the fans and work your way to taking the simple motor apart. Check for crud between the fan brushes and the rotating portion of the fan. The brushes are the grey graphite square things with springs. You will need to hold these spring loaded brushes back when you put the motor back together. Use a scotch pad to shine things up.

My cleaned out fan has lasted over 50,000 miles so far.

Also, all are correct when they say both fans should run at the same time. Furthermore, the loss of a fan can and will kill your compressor. If both fans are running, and you still have delay turn on issues, your compressor is shot. Been there, too.

Another note, if having your compressor replaced by a non-stealership, make sure you let them know that VW AC systems do NOT use pressure as an indication that the system is "full". A metered amount of oil and freon/whatever must be put in. Otherwise, you will way overcharge the system.

Also, just after my new compressor was installed, the clutch/pulley on the alternator went. The symptom was loud squealing whenever the AC was turned on. You can imagine how this symptom took us in the wrong direction. If you have high mileage, I suggest replacing the alternator clutch while the works are apart. I think it is a pretty cheap part.

I am still having a small problem with ice over on my new compressor. At the lowest fan speed traveling at night, the evaporator will freeze over the condensation into a block of ice, blocking all air flow. I have to shut the AC off and run the fan at full blast to melt it away. The stealerships have absolutely no idea how to fix this.
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