Bmw 318ti cooling fan new question
 

So I'm new to BMW but I have a new cooling fan question. So I bought my daughter a 318ti 1996 it has a 143000 miles and automatic. Here's the problem the fan only comes on with the a/c wait but it comes on with the a/c on and the fan is on LOW. I can jump it with the plug and a wire to her high fan speed but that's the only time there is high fan and there is only low fan with the a/c on. There is no fan with no a/c. Any help would be greatly appreciated. Oh yeah we did replace the whole cooling system i.e. Radiator,water pump,thermostat and housing and houses. Thanks again

If I follow it sounds like you need a new fan switch.

If your talking about the switch in the side of the radiator I replaced that as well when I replaced the cooling system. So as of now I have it temporarily spliced together so when the car is on it has full high fan on always. I tested both relays and have 12 volts at the high and low with either relay removed. If I unplug the plug that goes to the switch on the side of the radiator and turn the a/c on it still runs the fan on low? I also read that it should be on with ignition on car not started and a/c on but my fan is not on under those conditions. I only get low fan with car started and a/c on. Other then jumping high on with the plug. Any ideas?
Thanks

If you can make it work by bypassing the switch then you have likely found the problem.

Have you tried letting it idle with the AC on and switch plugged in. There's the possibility that you are not getting the car hot enough to kick the fan into high speed.

Only high works bypassing it and low only works with the a/c on. If I try and bypass to low it doesn't work. Also it's been this way through the AZ summer heat and only low on with a/c on and 112 outside literally. Also while I have you her car has always ran just past 12 on the gauge right next to the line the needle touching the right of the 12 mark. Everyone in here says they should run at 12 needle and line as one. I thought maybe when I replaced a the cooling system this would change but it didn't still ran exactly the same? Do some just run a tad hotter? Also I did use 50/50 BMW coolant when I replaced the radiator I self mixed I know it doesn't come that way. Thanks again for your replys. I've found a lot of difference's in these and American cars. My only complaint is this temperamental cooling system.
Thanks again

Got me on that one... Not sure how low works with the switch plugged in but does not work if you bypass the switch. Maybe look to the switch for the issue with the high and to a relay for an issue with the low. I had a failing relay cause the fan to stay on after the car was turned off and the key was out of the ignition.

The factory temp gauge is really an idiot light with a needle. The gauge has about a 45 degree range where it will sit at the 12 o-clock position. If you really want to find out what temps are doing get an OBD2 port wifi adapter and use a smart phone app to monitor water temps in real time.

Well here I'll really get you this confused the hell out of me. Low will work with the plug not plugged into the radiator. So a/c on car running plug undone and it's running the fan on low no plug? So it seems like it's doing nothing the plug except for letting me jump the fan to high. Could it be that this is a early 96 and maybe came with a clutch fan and fan off the water pump?

If it did have a mechanical fan it would have the aux fan in front of the AC condenser.

And it's not so it's not that. Have you ever heard of one working the way I described? With the plug out and still running on low with the a/c on?

I have not. I would start by checking as I described above.

Ok thanks I replaced the switch and had the old one that was in the old radiator and it did the same so. Nothing more I can do with the switch. I checked the relays as instructed by another member on another thread on here with a voltmeter. I guess I'll just buy the relays for the hell of it and give it a try. I did switch the a/c and low relays and the a/c still worked so I'll buy one and one of the magenta ones the high.

The fan will only run in low speed when the a/c is on.
The only time the fan will run in high speed is when the a/c fan high pressure switch is made.
Usually the high pressure switch will be closed when the a/c high side pressure gets over maybe 300 psi. When stuck in traffic and a/c full blast in Arizona heat.

When a/c is off, once engine temp gauge goes over half, the fan should run in low speed.
If it does not run in low speed with a/c off, there is a high speed fan relay with a normally closed contact that feeds the low speed relay.
The high speed relay closed contact could be bad.
Check the normally closed contact on the high speed fan relay first.

Is there a way to check that relay?

Yes.
According to the schematics, K22 is the high speed relay and K21 is the low speed relay. Test both.

Pull out K22 from the socket. K22 has two sets of contacts. NO and NC. (normally open and normally closed)
Terminal 30 and 87a is the normally closed contact. Should have continuity.
Terminal 30 and 87 is the NO contact.
If you put 12V at terminals 85 and 86, the relay should pull in and the NC contacts will open and the NO contacts should close.

K21 only has a normally open contacts (NO)
So you cannot switch these two relays.

Power distribution chart.