ac fan switch

I am working on troubleshooting my ac because it is 107F where I live. My fan/blower inside the car will run at all 4 speeds. however when I turn the AC switch on it will only stay lit up while in the #1 spot if you turn it up to 2,3 or 4 the ac light on the button will shut off..... Would this be caused by a faulty cooling fan switch?

Wow! I've seen some crazy stuff with the in dash fan switch and AC button switch, but nothing like this!

The cooling fan switch (in dash 4-speed switch) is a very flimsy constructed piece of junk to say the least. However, this doesn't sound like the switch.

Does the AC actually operate when the fan is in position 1? (confirmed that the AC Compressor is engaged and cool air coming out vents)

I'll need to get "my" schematics out and take a look. I feel pretty sure they are all the same from your model thru 2003 and maybe 2004.

Well, the fan Switch power goes to the Resistor Pack. In each position the current goes thru one or more resistors except for position 4 which is direct, no resistance , thus high speed full 12 volts. From the Fan Switch, in any of those positions, there is a circuit to the AC Button Switch. Unless the AC button is pushed in, that circuit is not complete to the Fan Control Module (under the battery) which kicks-in the AC Compressor and turns on the Fans out front.

So, contrary to how I was leaning in my previous post, yep, I believe it is the Fan Switch. .... not exactly a fun thing to change! It's been a while, but seems I have seen them on eBay.

As I said, the switch was either poorly designed or constructed. The switch is most often damaged by heat from the electric resistances at the contact point(s) which distorts the plastic. I've seen them that would operate (rotate thru the positions) but would not turn on the fan because the metal piece that supposed to be in contact with the positive strip was no longer in contact due to distortion.

I am new to working on Volkswagen so I am assuming the fan switch is located behind the 1-4 fan control selector right above the AC button? looks like a bit of a bugger to get out of there. Just so were on the same page this is the part you are talking about correct. https://www.partsplaceinc.com/vw-mk4-jetta-golf-heater-control-switch-19513.html

My AC currently isn't blowing cold air but I have a new Fan control module coming my way. I did a jumper wire to test both of my radiator fans and both speeds work great on those so I am hoping that FCM and new fan switch fix the issue. I also ran the jumpers from the battery to the compressor and the clutch would engage and disengage. May have to put some freon in the system an I am willing to bet it is low sounds like it hasnt ran for awhile. I just got the car and theres 330,000 on it and the last guy said the ac hasent worked the whole time he had it... Hopefully there isn't any bad seals. Will see.

Thanks for all of your help I was really baffled by this issue.

Yeah, that is the control and switch assembly. The center part (4-position fan switch) was available by itself for several years on eBay. I cannot seem to find one at the moment. However, I did find several offerings for that same assembly in the link you posted at a much cheaper price, made in China, no doubt. But, I suspect the one you linked is also made in China.

Also, when you are looking at your battery from the front of the car, notice on top under the center lid there should be three 30 amp fuses..... likely green since green represents 30 amp. The one on the left when facing the battery, is for the circuit that goes to the Fan Control Module. That circuit provides for the out front fan operation thru the FCM. That fuse is prone to corrode due to over heating ... if it has been over heating it will be quite evident. The other two fuses are for the ABS. (this info has nothing to do with your issue inside the vehicle)

And, there are two speeds on the Fans out front. As you saw, there are three wires, brown is ground and the other two are for low and high speeds. The slow speed is the one that goes bad, either by wearing down of the brushes or road debris getting inside the brush guides causing them to bind. Oh, and sometimes the resistor for low speed burns out. I have never seen a fan not work on high speed.
And, follow the two wires from the AC Compressor over toward the battery. There under or near the starter is a "bundle" with a connector that contains two wires that go to the Alternator. That connection seems to easily become contaminated and cause loss of connection....... generally an oily messy place to work.

Lastly, some where out there is an Outside Temp Sensor. It is generally located under the cowl on the left side of the car back close to the bottom of the windshield. If that sensor is bad or the wires have been chewed by a mouse, the AC Compressor will not kick-in. Assuming the refrigerant level is sufficient, the fans out front will come on when the Ignition is ON, AC Button Pushed in and Fan Switch ON any speed. The engine does not have to be running. If I remember correctly, if the fans do not come on (assuming good switch, good FCM, sufficient refrigerant, etc.), then the outside Temp Sensor may be the problem...

Hope this helps!

Hey thanks for all the help I was a little overwhelmed! That left fuse above the battery did get hot but looks like the last guy cut the wire right where it comes out of the box and did a jumper to the battery with a 30 amp fuse in line. Just to ensure that it was installed properly I checked it with the key on and there was 12V flowing through it.

Can the low speed fan resistor be replaced? If so I am assuming it is located on the back of the fan motor?

The resistor is internal.

The motor is stamped together. I have cut (grind) the tabs holding the two halves together to gain access. Typically about all that can be done inside is clean the brushes and guides of any road debris. If the resister is burned there's nothing that can be done. JB Weld will hold the two halves when it is reassembled!

Several of the vendors carry those fans and they can be found by doing a typical Internet search.

Well I replaced the fan switch and is still only working in position 1 however I also noticed the blower doesn't blow in position one but blows in 2,3,and 4... sorry I didn't notice this earlier. I have a new fan control module and passengers side fan ordered but don't think those would have any effect on the a/c button not working?? Is there an internal resistor on the blower that may have gone bad? Not sure why the blower not running would make the light come on.

Yes, on the bottom of the heater fan housing (above the passenger's feet) is a cover that contains three or four screws (8 or 9mm head). Take those screws out and the cover will drop down and out. It contains a Resistor Pack. The cover and Resistor Pack are one unit. It has a place for a four or five wire connector to plug into it. As I referenced above, the first three speeds go thru the Resistor Pack. Position 4, is a direct 12 volts that goes thru the Resistor Pack but not thru a resistance circuit. Amazingly, it is located inside the fan housing so that the moving air will keep it cool (resistance generates heat).

I seriously doubt the Fan motor is the problem.

The light in the AC On/Off button should only come on when you press the button in. Of course, the ignition must be ON and the Fan Switch must be ON (any position, low to high speed). It doesn't matter if the Engine is running or not. And, those fans out front should be On with the ignition On, Fan On and AC Button pushed in (On).

Measure the resistance from pin 2 of the resistor to pins 1, 3, and 4.
You should have continuity through all 3.
If you do have continuity then check the wires to the switch for continuity.

Thank you guys!!! Sorry it took me so long to get back to you I got tied up doing a few other things and finally got back to this. Replaced the fan control resistor pack this morning now I have the AC light on in all 4 positions and the compressor runs in all 4 positions also! Just need to take it for a drive and see if things are getting cold.

Thanks again for all the help!

Thanks for the Update ....
I've replaced a few of those resistor packs...

So now the AC light is on in all 4 positions, both fans up front are running and the compressor will engage and disengage with turning the ac on and off. However the air isn't getting any colder. I checked the low pressure side and I am at 30 PSI not sure what the high pressure side is. I am starting to think buying a high/low pressure gauge may be a good next step. would this be a step in the right direction? what should the high/low pressures be? Would this be a step in the right direction or is there something else I should be looking into?

Thanks

Branhamd, the low side pressure needs to be about 45 PSI with an ambient temp of 80 to 85f. The high side pressure should be 250 to 275 at the same ambient temp (300 psi is okay). 30 psi is generally an indication of low refrigerant. Is the return metal pipe cold? If the humidity is relatively high and the AC is working properly, that pipe should be sweating-cold.

Yes, a manifold gauge set (with both high and low gauges) will give you much more info. Learn to use it and be safe.

So I had a strange issue while charging. With the car up at operational temp I pushed the AC button on and the fan turned up to 4 I hooked up the low pressure port like normal and it took freon until it hit 38 PSI then it stopped and wouldn't charge anymore with lots left in the bottle.. Could this be a bad o-ring somewhere?

The car now blows cold air but I would like to charge it up to the proper pressure.

If it blows cold air, leave it alone!

Hahaha ok will do!

branhamd said:

So I had a strange issue while charging. With the car up at operational temp I pushed the AC button on and the fan turned up to 4 I hooked up the low pressure port like normal and it took freon until it hit 38 PSI then it stopped and wouldn't charge anymore with lots left in the bottle.. Could this be a bad o-ring somewhere?

The car now blows cold air but I would like to charge it up to the proper pressure.

Click to expand...

The AC should be charged by evacuating the charge and adding the needed freon measuring the weight of the holding tank.
Basically a charging system is needed to do it properly.

If it's blowing cold you may be close to proper charge.