2002 Golf High Speed Fan Issue

I suspect FCM for this set of issues. Scenario is as follows:

When you turn on AC, low speed fans come on. When car runs a while or heats up, they turn off and AC compressor starts to high cut off since there is no cooling across condensor.

I pulled the radiator thermal switch. Shorted low speed, they turn on fine. Shorted high speed, they turn on briefly then off. Same behavior. It makes 3 distinct clicks. FAN ON, FAN OFF, then another click (why?) with no response from fans.

I suspect FCM at this point. Fans are nearly new. I haven't had chance to run them on high from battery directly or anything like that. I thought maybe in rush current. I unplugged the fans. Same behavior. 3 clicks, then nothing. When you release the contact, 3 clicks, then nothing.

AC on, or off, causes same behavior. 3 clicks, fan briefly turns, then off. 3 clicks each time.

Thanks for any advice! I'm not sure how it could be anything other than the FCM, short of some strange shorting between it and the fans. Or some other ground issue, etc. Easy stuff first. The FCM is originaly to the 482k mile car

Thanks

An update. Replaced the FCM with a knock off 25 dollar one, didn't work when commanded AC on. Then replaced with a real german made one, FEBI-STEIN or something. It worked at first but when things heat up it doesn't. This is really strange problem.

I will check again today but when it's in this condition, I can pull thermo switch off radiator and it will run fine in low and high speed. I'm thinking maybe somehow, only when hot, the signal from AC drops out. Not sure why. Keep in mind when this does happen the AC compressor cycles on and off, due to high pressure I'm assuming. One thing haven't checked if ECM is commanding AC off due to perceived engine overheat. Hmmmm...

I think FCM is ruled out. Someething else going on with wiring. The fans are fine too.

I may just end up running bypass wire to command low speed fan on, this is old car 486k miles.

Thanks

Have you checked your A/C charge? Seems I recall if the charge is low the compressor will turn off when pressures are out of sync. That would cause the fans to stop as well.

I wish it was that simple! No I don't think I had 55PSI Low side. It runs fine and ice cold on highways. When you park the car, as it warms up, eventually the fans will shut down while AC clutch continues to run. Then the AC clutch will cycle on and off due to high cut out, I assume. It's a really strange condition. I think I can start the low and high speed fan via jumpering the thermal switch. Most things I know of, conditions for AC clutch, are for the compressor not the low speed fan. So I'm stumped. It's never easy with these crazy things. I've checked all basics. I'm wondering if I somehow am loosing the signal from the AC switch but if that were true the clutch would not cycle. When it does cycle under no fans, the fans DO NOT come on. Gotta be some crazy wiring issue or potentially the fans themselves. However they both do not turn on when this happens. I will verify I can force them on with thermo switch jumper in a little while. But then a brand new FCM shouldn't have problems turning them on. Hmmmmmm

I started it at lunch it was running fan, fans cycling between low and high speed pretty quickly every 10-30seconds. The engine was not warmed up so I wouldn't expect high speed fan at that time. Could be a clue. I don't think the AC condensor would heat up the radiator enough to trigger the high speed fan. But once it was warmer the low speed fans just cut out entirely. When this happens I want to jump thermoswitch to see if I can run them that way.

Engine off and cold. Key on. No low speed fan. Fuse is fine. When I unplug and replug back in the high speed cut off sensor it comes on just briefly then dies. Ideas? I wonder if this is bad.

I can jump low speed on from thermoswitch. When I jump high speed it comes on briefly and shuts down with same ole 3 click of relay.

I have my golf here that works. This is a friends I'm working on. Can that pressure switch be removed without releasing all refrigerant?

I wanted to post results, finally figured it out. The power supply 40A fuse for high speed fan wasn't making good contact. I had aftermarket box which wasn't perfect dimensions so the small washer was making it not make contact due to the stupid shoulder raised on it. So I removed it and all was good. Once the high speed fan had power, the low speed and FCM functioned properly and all worked. It is strange to me that the high speed fan power supply affects operation of the low speed fan, that made troubleshooting difficult as I assumed it did not. Ugh

There is one small issue though. When running the AC, the low speed fan cycles to high speed then back to low every minute or so. It's not power related as I can force the high speed fan on through the thermoswitch. I suspect the DUTY CYCLE signal from the high pressure sensor is either out of range, or the pressure isn't getting high enough to sustain high speed fan. Thoughts? I have another golf I recently got and it runs low speed fan then switches to high speed and runs more continuously, in 90 degree heat anyway.

Thanks for the help!

The 40 amp fuse provides power for the fans through the FCM.
If the FCM is not getting enough power because of the bad connection the fans won't work.

Yes but it seems it would only affect high speed fan events. It doesn't it effects low speed also.

I wish we had a schematic for stupid FCM would have been much easier to troubleshoot. Just stabbing in dark otherwise.