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Intermittent Aircon Fan

NathanG
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NathanG Rising Star

NathanG

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Morning all,

 

replaced my rad over the weekend, nice and easy job but i noticed when i ran the car up to temp i didn't hear the fan kick in, i wasn't bothered by that as after owning the car in 4 years I've never hear the rad fan at all and i've left in on tick over on the drive for 4 hours with 15mins revs in-between and the temp gauge never went over 90 degrees.

 

Anyway, while the car was ticking over while bleeding the rad i decided to turn on the aircon.....nothing.  Didn't get cold or anything.  I just assumed that it needed regaling again so started packing up my tools.  All of a sudden the aircon fan kicked in, stayed on for about 10 seconds then turned off again. I left the car running and it appears that every 1-2 mins the aircon fan kicks in for 10 secs then cuts out, it continues this behaviour until i turn the aircon off.

 

So to sum up, my rad fan does not appear to work at all and my aircon fan comes on for 10 seconds ever 1-2 mins or so.  Does anyone have any ideas what this could be.  Ive had a look and people have suggested the module or the fans its self or could it be something else.

 

Thanks for reading.

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Breezy_Pete Veteran

Breezy_Pete

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Have a look how many wires the AC fan has, going into the centre bit of the fan (will be either two or three).  If it's only single speed (2 wires), then it's just your main fan that's lost its low speed, seems to be a common thing. 

See recent AC thread for testing methods and cheap repair option. http://www.briskoda.net/forums/topic/397269-air-con-troubles/

Edited by Wino
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NathanG Rising Star

NathanG

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Have a look how many wires the AC fan has, going into the centre bit of the fan (will be either two or three). If it's only single speed (2 wires), then it's just your main fan that's lost its low speed, seems to be a common thing.

See recent AC thread for testing methods and cheap repair option. http://www.briskoda.net/forums/topic/397269-air-con-troubles/

So if the main fan doesnt work that will affect the air con fan also causing it to only come on for seconds at a time would it. I shall go and investigate the aircon fan now.

Appreciate the help mate.

**edit**

Just checked and i have 3 wired going to the aircon fan.

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Edited by NathanG
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Breezy_Pete Veteran

Breezy_Pete

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Both fans should do the same thing at the same time, if both are two-speed.

If your main fan never comes on, and the small/AC fan only for very brief moments, I wonder if your main fan is doing neither of its speeds, and the AC fan is only working at high speed.

 

Test using the method of unplugging the thermoswitch connector, and linking the brown wire pin to each of the other two pins, first one, then the other, with ignition switched on. One of them should put both fans on at low speed, the other both at high speed.  Depending on what you see there, you'll know more about the state of play.

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NathanG Rising Star

NathanG

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Both fans should do the same thing at the same time, if both are two-speed.

If your main fan never comes on, and the small/AC fan only for very brief moments, I wonder if your main fan is doing neither of its speeds, and the AC fan is only working at high speed.

Test using the method of unplugging the thermoswitch connector, and linking the brown wire pin to each of the other two pins, first one, then the other, with ignition switched on. One of them should put both fans on at low speed, the other both at high speed. Depending on what you see there, you'll know more about the state of play.

Something tells me i should have done this while the bumper and undertray was off haha. Not a lot of room to manoeuvre to get to the switch as it it bit i shall have a go. Thanks again.

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Breezy_Pete Veteran

Breezy_Pete

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Yeah, access to the thermoswitch connector isn't easy on most models, possibly from below is usually easier once undercover is off.

Make sure fingers aren't in the way of any fan blades before shorting out any connector pins, whichever way you go in from... :eek:

Edited by Wino
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NathanG Rising Star

NathanG

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Oops my mistake, just went and had a closer look at the Aircon Fan and it has 2 wires not 3. Sorry lack of sleep and not the best light played tricks on me. Its only 2 wires 100% positive on that.

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Easy mistake to make. In that case it's just your main fan that's lost its low speed.  I'd fit a resistor like del-gti did in post #46 of that other thread, and I did on my Polo last weekend, and I hope to do to the missus's car this weekend coming...

 

On the other hand, it being a diesel, and one of the fans at least is working when asked to, it may not be necessary to fix anything really, unless you spend time in slow-moving traffic regularly. Check if the main fan will come on at high speed maybe (via the thermoswitch connector), to confirm you have that in hand if things get really toasty. 

 

I would guess that the AC fan (and the other but without effect) is getting triggered by the refrigerant pressure rather than coolant temperature, which may be why it runs in such short bursts, because the pressure soon dips once the fan shifts some air. If you've got VCDS you can watch the pressure reading from G65 in one of the HVAC measuring blocks, on my Polo it seemed to trigger the fan at 16 bar.

Edited by Wino
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NathanG Rising Star

NathanG

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Easy mistake to make. In that case it's just your main fan that's lost its low speed. I'd fit a resistor like del-gti did in post #46 of that other thread, and I did on my Polo last weekend, and I hope to do to the missus's car this weekend coming...

On the other hand, it being a diesel, and one of the fans at least is working when asked to, it may not be necessary to fix anything really, unless you spend time in slow-moving traffic regularly. Check if the main fan will come on at high speed maybe (via the thermoswitch connector), to confirm you have that in hand if things get really toasty.

I would guess that the AC fan (and the other but without effect) is getting triggered by the refrigerant pressure rather than coolant temperature, which may be why it runs in such short bursts, because the pressure soon dips once the fan shifts some air. If you've got VCDS you can watch the pressure reading from G65 in one of the HVAC measuring blocks, on my Polo it seemed to trigger the fan at 16 bar.

Ahh, all very good info. I shall look at the resistor fitting as well.

In your second paragraph you mention that one fan works when asked to. My problem with the aircon is that it blows ice cold for 3 seconds when the fan kicks in and then 'warms' back up once its stopped working. When i want aircon on i dont want it to turn itself off haha i want it to stay on until i turn it off.

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Well I'm not sure exactly what's going on with your AC TBH, but it can't possibly be a bad thing to have both fans working as they should be, so I suggest fixing the main fan and see how things behave when that's working right.

Edited by Wino
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Dazza95 Rising Star

Dazza95

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Well I'm not sure exactly what's going on with your AC TBH, but it can't possibly be a bad thing to have both fans working as they should be, so I suggest fixing the main fan and see how things behave when that's working right.

I second this, if the pressures are too high the AC compressor can't load properly and provide the required cooling, more noticeable in the warmer weather we've been having. I seem to remember reading on another forum that the compressor will shut off if the pressure gets too high which would make sense.

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Breezy_Pete

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When I popped out to mine the other night 3hrs or so after its last trip, G65 was reading about 5.5 bar, I think, give or take. Highly temperature-dependent, I'd think. Ignition had to be on to make VCDS work, but engine was off.

Edited by Wino
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Dazza95 Rising Star

Dazza95

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Yes it's temperature dependent and it can give you a rough idea of the charge in the system, see table below of where the pressure should be for corresponding ambient temperatures:

 

post-128257-0-89724400-1465514340_thumb.png

 

These are when the system is not running of course.

 

Read more: http://tinyurl.com/jdce5bp

Edited by Dazza95
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From what I can gather from watching pressure numbers on VCDS, the fans are triggered to spool up at low speed when the refrigerant pressure exceeds 9 bar (de-activating if it drops below 6.2 bar due to natural movement-caused airflow coupled with low demand on the system). At 16 bar high-speed fan operation seems to be triggered, not sure on the switch-back-down-to-low-speed pressure yet, forgot to press "Start" on the log where that happened on my Polo prior to fan mending. A couple of logs from different cars, both in one spreadsheet, with some notes in red, here.

 

Evening commute home in much warmer conditions now added to that log file. Fans ran all the way home once G65 registered 9 bar, as it never dropped below the switch-off threshold. 

That must be why I had such an uncomfortable journey with a carful of people the other week, when my main fan wasn't working on low speed and the AC fan was 'limping' along on 2 out 4 brushes. 

Edited by Wino
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