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My Fan and AC Experience

2928 Views 2 Replies 3 Participants Last post by  Thejarhead
Help with the Fan / AC issues

Recently I purchased a 2001 NB for my daughter. I have to say this Beetle might be the most fun to drive car I have ever had. It is quiet, and ours has the sunroof and leather which just finishes it off. The car hugs the road and is a little powerhouse going up hills and down the highway. We love it.

When we looked over the car at the dealership, I neglected to try the ac on the car before we purchased it. The owner of the little dealership must have been on his knees praying in his office while we test drove the car. His prayers were answered, we purchased it.

The drive home took about two hours and my daughter and I had a smile all the way. The weather was cool and we had the sunroof open for the drive with the windows cracked a little to stop the annoying suction on our ear drums.

But a few days later, the weather started to warm up and my daughter turned on the ac and didn’t get any cold air. So, later on, I popped the hood and checked to see if the ac clutch was engaging. It wasn’t. Since the car was a new make and model for our family, I went looking for help on the internet. I ran across this forum and am glad it is here. I searched out many posts which dealt with fan and ac problems.

I want to post my experience as a help to the many who continue to be frustrated with their Beetles when the ac stops working or the fans don’t turn on. Many people have cursed their own cars when they can’t figure out what the problem is. Some actually saying they hate their car. These are wonderfully made cars. The engineering behind them is a wow.

The Volkswagen electrical system seems ridiculous at first until one realizes what the intent of the design is. Then it falls into place. Are their goofy things about the electrical system? Yes. The fuses over the battery is plain dumb. But once one sees what the intent is and how the system works, troubleshooting isn't that hard.

As many posts have spoken out already, there are some basics you need to understand in troubleshooting the ac and fan situation.

They are as follows;

When you turn on the ignition switch, and the ac switch in the on position, and the fan control is on one of the multiple speeds, the fans on the radiators should be turning in the slow speed.

This is how VW designed the car to operate. AC on. Check. Fan control turned to one of the speeds. Check. Car running or ignition switch on. Check. The fans should run at slow speed.

VW knew the ac would cause the engine heat to rise over specifications, especially if the car isn't moving. This is why the fans come on with the ac on.

Also, the fans do not stay on after the key to the ignition is turned off. The high speed fans can come on after, but not the low speed.

Each of the two fans are two speed by design electrically. They are both wired together so that when one is running, so is the other. If one is running at slow speed, the other is running at slow speed. The same is true for high speed.

Each fan has internal resistors for slow speed operation. At high speed, the fans bypass the resistors. This is done purely through the wiring of the external circuits to the fans.

Now, when I realized neither of the fans were operating, I made the compressor clutch a secondary issue. I knew that VW wouldn't let the compressor run unless the fans were running.

The logic for this operation is controlled through a device called a Fan Control Module. (FCM) These are mounted right under the battery tray on many models of the beetles.

Before you go and start troubleshooting the electrical system, I can't say any more clearly, you should make sure the refrigerant level on your ac system is within VW specs.

Could you have a blown fuse somewhere? Yes. There are many posts dealing with this issue on this site. I am addressing the ac and FCM issues.

There are a number reasons I say this. In troubleshooting the VW system, the very basic design calls for proper levels of the inert gas in the ac system. It is monitored and if not within guidelines, the rest of the system will not operate by design.

Did I follow my own advice as I began my journey to fix my daughters car? That would be a big fat no.

I ordered up an aftermarket FCM through eBay and was happy when it showed up within a couple of days. I took out the battery, removed the tray and all the associated wires, where I could then get to the FCM mounting hardware. I swapped out the unit and when I wired up the battery, the AC clutch snapped shut and the aux water pump began to run.

I thought, “Great, everything is working now.” Little did I know that it wasn’t working at all but the new FCM was bad.
The ignition switch wasn’t even on and the clutch was engaged and the aux water pump was running. Soon after, I realized the error when the battery was dead. This caused me to really study out the electrical system on the car to decide what had gone wrong. I clearly didn’t want to believe the new FCM was bad.

There are many of you who have posted that you have no slow speed movement on your fans when the ignition key is on.

There is a quick test to find out if the problem is the fans or something else like the FCM module. I want to tell you how I determined whether the fans were were bad or not quickly.

If you jack up the car in the front and put it on jack stands in a safe manner, you can crawl under the drivers side where the battery tray sits and you will see two connectors hanging down from a rectangular plastic box. This is the FCM. One connector has 4 large wires coming out of it and the other has 14 small wires.

Reach up and disconnect the large connector by squeezing the thumb release and pushing up on the connector. You should hear a click when it releases and then you can pull it apart.

There is live voltage from the battery on this connector so do not let the pins inside touch anything on the frame of the car or anything grounded. You will definitely wish you hadn’t as sparks will fly.

There is a smaller wire in the middle of the 4 conductor connector which is red / white. Assuming your battery is still in the car and it is hooked up property, you can take a piece of wire from the positive terminal and being very careful, touch it to the terminal inside this connector which attaches to the red / white wire. The fans should turn on in the slow speed mode.

If they operate as designed, then this tells you the fans are working properly and the problem is related to the Fan Control Module. It doesn’t mean the FCM is bad at this point, it just means there is something else going on causing you to not have any voltage out of the FCM to the fans.

You can leave the 4 conductor connector loose for now. Disconnect the 14 pin connector from the FCM. You need to be very careful in this test as you can take out your ECM on the car or create other problems if you don’t take care in reading voltages without shorting pins together.

The next test is to determine if the FCM has the signal levels it needs to turn on the fans.

Hook up your meter to pin 8 of the 14 pin connector and have someone turn on the ignition switch without starting the car. Have them turn off the ac button and turn off the fan switch. You should have no voltage on this pin currently.

Then have them push in the ac button and turn the fan on to any speed besides off. You should read around 12 volts. If you do, this test passes. If not, then there is a problem with the electrical system from the battery to the ac switch, through the fan switch back to the FCM.

Unless you have torn a NB dash apart, I would suggest a dealership fixes this problem for you. For the brave, you would need to find out where the break in power is to or from the ac switch module. It could be as simple as fuse S225 being blown, a bad switch, a bad fan control switch or a break in the wiring.

The FCM looks at pin 4 of the 14 pin connector for 12 volts to supply its circuitry. Check this to make sure the FCM has a supply voltage of 12 volts now. If not, you will need to determine why not. It is supplied with a 30 amp fuse S16 over the battery.

The FCM needs to have a good ground. You will find this on pin 6. You should be able to check for continuity between pin 6 and the chassis ground. If there is not a good ground, you will not get proper operation out of the FCM.

What was frustrating to me is that the original problem was no ac. Now I had a new problem. My aux water pump was running and so was the clutch on the AC compressor, even with the ignition off. That should have immediately told me the FCM was bad. I didn’t know what to do at that point. Again, I assumed the FCM that I had replaced was good. It wasn’t.

There should never be a time when the clutch on the ac compressor would be engaged without the ignition key on. I had that, as well, the aux water pump running continuously. And as a side note, the aux water pump is designed to run for ten minutes approximately after engine is shut down. I believe this time is set by the Fan Control Module.

I took the car into a local garage who specialize in Subaru’s. The owner was happy to assist with the ac service as his machine is universal for all brands of cars. When he hooked up the machine to my beetle, the gauge on his ac machine showed a very low pressure only registering .2 ounces of refrigerant.

Clearly this is not enough for the system to work properly. I asked him if he would put dye in the system so that I could see if there is a leak in the future. He did that at no additional cost.

What is interesting is that the moment he disconnected the hose after refilling the system, the refrigerant came spraying back out. The valve where he filled was bad. This is probably where my original problem came from. And I had bypassed doing the obvious first in checking the refrigerant level. He replaced the fitting for six dollars, filled the system back up and I was off. The ac worked perfectly and I was happy that the car was fixed.

Until that evening when I realized I had a dead battery again. The compressor clutch was still on and the aux water pump was still running. It was then that I realized the FCM was bad. I wondered if the first one was bad. So, I climbed down underneath the car and pulled the connectors of the new FCM and put them back on the old one. The compressor clutch was not engaged and the aux water pump wasn’t running.
Finally! I swapped out the two FCM’s, putting the old one back in and the car is now running perfectly again.

There is no substitution for troubleshooting the car in a proper order. If you are having fan problems. You will need to first determine if the fans are working properly. The high speed fan test is different than what I have described earlier. In order to test the fans at high speed, the easiest way to do this is to pull the connector on the temperature switch which is mounted in the radiator right below the FCM. It has a 3 conductor connector and isn't easy to get to. But doable.

If you pull the connector, you will have direct access to the wiring going into the high speed and low speed sides of the fans.
Turn on the ignition switch and short pins 1 and 2. You should note both fans coming on in slow speed. Then short the wires on pins 2 and 3. You should see the fans operate at high speed. If not, there is a wiring issue or a fan issue on your vehicle outside of the FCM.

The switch that you just disconnected the connector from is what controls the fans at high speed. If the radiator temperature exceeds a certain temperature, the fans are called on to cool the engine. The Fan control module does not control the high speed side of the fan operation. Only the low speed.

There are fuses in line with the fans. One is fuse 16 inside your car in the fuse panel behind the drivers door. The other is fuse is over the battery in the engine compartment. The five wires on top are wired over fuseable links. You will notice the different diameters of the flat strips under the nuts. Those have numbers on them and that is the amperage rating of each fuseable link.

I hope this helps many people to figure out why their fans aren’t coming on. By the way, the replacement FCM I purchased was inexpensive on eBay. After taking it back out, I took it out of the plastic housing to see if it was designed by the same mfg as VW. It was radically different in design and I am not surprised it didn’t operate as advertised. Some company decided to build an inexpensive replacement and sell it against the price that VW gets. This is clearly a situation of getting what you pay for.

I am not a VW tech nor a mechanic. Use common sense when working on your vehicle and do it in the safest manner possible. Your life is important.
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Excellent write up! Thanks for the hard-earned education!
Well written, and very explanatory. Thank you.
Also you've just experienced the failure of cheap chinese ebay/amazon parts right out of the box. All to common an occurrence. So I think of ebay/Amazon as the last resort when buying car parts of any kind.

Just for future reference, here is the mega thread that covers MK4 AC over at tdiclub.

Check your radiator/condenser fan operation NOW - TDIClub Forums
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