NO A/C on Fan speed 2-4 works Fan speed 1

oliveone · Apr 17, 2010

Back ground 1999.5 Jetta with 241,000 mile runs great. I have owned the car since 37,000 miles. The AC system is having an issue that I cannot seem to figure out. When the heater/AC blower fan is on one the AC works ( The compressor is engaging and the system gets cold). I have checked the A/C high and low sides and both are good. The radiator fan starts as soon as the AC button is pushed and when blower fan is on one. Note on heater/AC blower fan setting one the fan motor that is used to push the cold air is not working. The AC is getting cold but no fan to push around the car. When I turn the fan speed to 2-4 the fan blows as normal but the AC turns off ( light turns off for AC, fan under hood turns off and compressor turns off). Every now and then the AC will work in 2-4 on blower speed. When it was 79 last week and the AC would not work for the 3 hour drive it was on was a PITA. I have taken the dash apart to check the back of the HVAC head unit and did not find anything loose. Any help would be great.

Jason

TDI_bubble · Apr 17, 2010

I'm in the process of charging my AC right now, my issue is the fan only works on 4. I would assume either the switch or the fan resistor is out. I haven't taken the switch out to test it yet though.

As for your issue I would check the fan switch first, seems like its an issue with the A4's.

Alright my AC's kick'in out 45*F of pure awesomeness. I found out a quirk with the switch, while it's on the number it doesn't work. In between the numbers/clicks it works like it should. Seems the contacts wear out on the switches. At least I know its not a resistor issue! ($120).

oliveone · Apr 20, 2010

back to the top

DanG144 · Apr 20, 2010

This is either the fan switch, or more commonly, the cabin fan resistor bank blown. If you buy a Bentley manual (recommended) and look at the circuit diagram you will see why this is the case. There are many, many threads about this problem.

The common cause of the fan resistor bank to fail is due to decreased air flow from the fan - draggy bearings for instance. The resistor bank sits in the airflow from the fan discharge.

So quite often to fix this, you need to replace the resistor bank and the fan. Sometimes simply lubricating your cabin fan bearings will fix the draggy fan problem - but if it does not then you will very soon be buying another resistor bank.

Again, depending upon your skill set, you may be able to repair the resistor bank. Sometimes it simply needs resoldering, sometimes it needs a new fuse and resoldering, sometimes it needs a resistor and resoldering.

mrGutWrench · Apr 20, 2010

DanG144 said:
This is either the fan switch, or more commonly, the cabin fan resistor bank blown. If you buy a Bentley manual (recommended) and look at the circuit diagram you will see why this is the case. There are many, many threads about this problem.

The common cause of the fan resistor bank to fail is due to decreased air flow from the fan - draggy bearings for instance. The resistor bank sits in the airflow from the fan discharge.

So quite often to fix this, you need to replace the resistor bank and the fan. Sometimes simply lubricating your cabin fan bearings will fix the draggy fan problem - but if it does not then you will very soon be buying another resistor bank.

Again, depending upon your skill set, you may be able to repair the resistor bank. Sometimes it simply needs resoldering, sometimes it needs a new fuse and resoldering, sometimes it needs a resistor and resoldering.

__. This is a Very Good Answer. All I'd add is that the "1-3 no fan but A/C cool air blowing through by "ram air" when the car is moving and 4 fan running but no A/C" symptom is a classic sign of a blown resistor set.

everyman · Apr 20, 2010

DanG144 said:
..
So quite often to fix this, you need to replace the resistor bank and the fan. Sometimes simply lubricating your cabin fan bearings will fix the draggy fan problem - but if it does not then you will very soon be buying another resistor bank..

How much of a nightmare is it to get to the blower fan? Is it an individually serviceable part? I've been having the issue where the insulation in the heater box breaks down and blows out through the vents, very annoying. From what I understood that whole box is a single part. That would have to be replaced. Is the fan at least a separate part?

DanG144 · Apr 21, 2010

The fan is a separate part.

I have never removed one, but others have. Search for threads discussing it.

mrGutWrench · Apr 22, 2010

DanG144 said:
The fan is a separate part.

I have never removed one, but others have. Search for threads discussing it.

__. Yeah, I have (and discussed it in other threads). There's a very good "how-to" with pictures on Vortex. You have to remove the center console (on an A4 with manual transmission, anyway) then pull the glove box; once you've gotten there, the actual blower (and access to the central plenum box) is a snap. It's "fiddly" and a little complicated but it really didn't take long and it wasn't difficult.

oliveone · Apr 22, 2010

Ok so I pulled the heater control wire off and hooked up to the new heater control unit and the AC did not work. I checked all wires and could not find anything wrong. I checked the Fan Resistor Pack and the plug looked good. Once removed found that it had gotten wet and rusted. I will have the new resistor pack tomorrow and will let you know I it fixes it.

Jason

everyman · Apr 22, 2010

mrGutWrench said:
__. Yeah, I have (and discussed it in other threads). There's a very good "how-to" with pictures on Vortex. You have to remove the center console (on an A4 with manual transmission, anyway) then pull the glove box;....

Did it look like it might be possible to replace the door sealing foams that deteriorates? It's not the hugest issue in the world, but it's super annoying because it comes out all over the place every time I turn it on, including in my face

bugsTDI · Sep 5, 2014

oliveone said:
Ok so I pulled the heater control wire off and hooked up to the new heater control unit and the AC did not work. I checked all wires and could not find anything wrong. I checked the Fan Resistor Pack and the plug looked good. Once removed found that it had gotten wet and rusted. I will have the new resistor pack tomorrow and will let you know I it fixes it.

Jason

I know it's been a while, but what was the final fix for this? Mine's doing the same thing.
Thanks!

jfire · Sep 22, 2014

I'm having the same problem! Ac only works on fan speed 1, and fan doesn't run. Fan will run fine on speeds 2,3,4 but the ac turns off. Awaiting his outcome before changing the resistor bank and motor.

flee · Sep 22, 2014

Probably just the resister pack, only around $50 or so.
It's very easy to get at under the dash in front of the glovebox. There is some insulation in the way.
Or you could do what I did, remove the center consoles, armrest and glovebox...

fruitcakesa · Sep 22, 2014

The fan in my sedan was only blowing on 4. 1,2 and 3 were NFG.
I replaced the resistor pack and lubed the fan bearings.
It all works now but, since I am not sure why the resistor failed in the first place, I cheaped out and bought a no-name resistor from a non forum source for $11. If it fails again then I probably need a fan and another resistor.

Palfen · Nov 10, 2014

It is the resistor pack!

jfire said:
I'm having the same problem! Ac only works on fan speed 1, and fan doesn't run. Fan will run fine on speeds 2,3,4 but the ac turns off. Awaiting his outcome before changing the resistor bank and motor.

I had exactly this problem, changed the resistor pack and now it works like a charm! No need to change the motor, just the resistor pack.

Tom W. · May 1, 2017

So, the fan only blows on 1- the knob turns to the other settings, but whether heat or A/C
only the lowest speed works. Could this be the resister pack as well? or is something wonky with the control/ knob?

AnotherPerson · May 1, 2017

Do our cars use the resistor for top speed? I know most it's straight power which is why many old cars only have high speed.

Sent from my iPhone using Tapatalk

Tom W. · May 3, 2017

resister top speed

pretty sure the top speed is without any resistors. That is why I am thinking that the problem for me is not in the resistor pack but in the control switch

Tom W. · May 3, 2017

clip in back

found a video, often times the problem is a clip comes off on the back of the control, so the control nob really doesn't do anything- solution is to pull the panel, glue the clip back on.
http://www.bing.com/videos/search?q...00200B97A652D6C8513F00200&fsscr=0&FORM=VDMCNL

Jamierara · Dec 6, 2017

http://forums.tdiclub.com/showthread.php?t=483314

This is how you can diagnose it without having to take it all apart.

NO A/C on Fan speed 2-4 works Fan speed 1

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