HELP!! Aux fan comes on high as soon as car started

[ninetyseven1]

Jim, i will retest again. I do remember if i removed low speed relay that fuse was fine IIRC but i will test again to be sure.

[ninetyseven1]

Yes, disconnect the switch you added.....then.....
If F7 still blows pull out the low speed relay.
If F7 still blows then the you have a short somewhere between F7 and the relay socket.
If F7 doesn't blow then you have a short between the relay socket and the resistors mounted on the fan frame.

So, Jim. Just to clarify , if I do find the issue to be between the low speed relay terminal 87 and the brown/black fan wire. Would I just need to run a new ,proper gauge wire directly from that terminal to the fan? correct?

[JimLev]

So, Jim. Just to clarify , if I do find the issue to be between the low speed relay terminal 87 and the brown/black fan wire. Would I just need to run a new ,proper gauge wire directly from that terminal to the fan? correct?

Probably, but first...
Got an ohm meter? Pull K21 (low speed relay) out of the socket and read from terminal 87 to chassis ground. Should read (I'm guessing, my fan is PWM, not a 3 speed like yours) something like 5-10 ohms, not a dead short.

Before you replace the wire check the connection where the black/brown wire from the relay socket connects to the resistor (X82 pin2) on the fan frame just to make sure it's not shorted to ground at the resistor connection or thru the resistor if it's burned up.
The resistor has a metal case with a wire coil inside, it's possible the wire could be shorted to the case which is mounted to the fan frame when is bolted to the chassis.

[ninetyseven1]

Probably, but first...
Got an ohm meter? Pull K21 (low speed relay) out of the socket and read from terminal 87 to chassis ground. Should read (I'm guessing, my fan is PWM, not a 3 speed like yours) something like 5-10 ohms, not a dead short.

Before you replace the wire check the connection where the black/brown wire from the relay socket connects to the resistor (X82 pin2) on the fan frame just to make sure it's not shorted to ground at the resistor connection or thru the resistor if it's burned up.
The resistor has a metal case with a wire coil inside, it's possible the wire could be shorted to the case which is mounted to the fan frame when is bolted to the chassis.

ok, just so you know, the high speed resistor has always been missing. I do have a brand new one ready to install though. The low speed one was fine until this event happned and now it is blown so i have bypassed it as well. I will test and report back

[JimLev]

So you bypassed the both resistors and the low speed relay connects directly to the fan??????

[ninetyseven1]

yes, i did that after the low speed resistor blew due to this stupid toggle switch idea i had. so now instead of just one low speed resistor they are both bypassed.

[JimLev]

yes, i did that after the low speed relay blew due to this stupid toggle switch idea i had. so now instead of just one low speed resistor they are both bypassed.

You should have mentioned that a long time ago.

That's why F7 blowing the fuse. The fuse for high speed operation is a 50 amp fuse. Look at the schematic, it should make sense.
Your trying to run the fan with both resistors bypassed which amounts to the fan running from the low speed relay circuit but sending power directly to the fan motor which is high speed.
From a dead stop the fan will require more than the 20 or 30 amps thru what ever fuse you have in F7 now.
Don't replace F7 with a 50 a fuse, the wires for F7 and the low speed relay are probably not rated for 50A.
Put the resistors back in.

[ninetyseven1]

You should have mentioned that a long time ago.

That's why F7 blowing the fuse. The fuse for high speed operation is a 50 amp fuse. Look at the schematic, it should make sense.
Your trying to run the fan with both resistors bypassed which amounts to the fan running from the low speed relay circuit but sending power directly to the fan motor which is high speed.
From a dead stop the fan will require more than the 20 or 30 amps thru what ever fuse you have in F7 now.
Don't replace F7 with a 50 a fuse, the wires for F7 and the low speed relay are probably not rated for 50A.
Put the resistors back in.

So , then that explains why the other day when fuse 7 kept blowing i tried a 30 amp fuse and while it didnt blow, the fan went directly on and it went on high as soon i turned the ignition into position 2, this is without the ac even being on. Make sense? I do have a brand new 0.2 ohm 100watt resistor for the high speed that just came in the mail. can i run this one resistor without using the low speed resistor just for testing purposes?

[JimLev]

Might as well mount the resistor on the fan frame and test it out. It needs to be mounted to dissipate the heat or it will burn up.
Not knowing what the ratings for the wire and relay are I wouldn't run it for ever like this. After a minute of running see if the wires get hot.
So far you've only blown fuses and not burned the car up so a quick test should be OK.

[ninetyseven1]

Jim , yes the low speed resistor blew when I tried that toggle switch so
Ur saying the reason f7 kept
Blowing was due to having bypassed both resistors ?

[JimLev]

Most likely it was. The motor starting on high speed from a dead stop will draw a lot of current.
Typically the motor will be running on low speed then switch to high speed when the temp sensor detects the coolant temp is exceeding the hi temp set point of the switch.
With the motor already running at low speed it won't draw as much current when switching to high speed like it does from a dead stop.
Why is the fan even running when you turn the key on? Did you jump the sensor? The fan shouldn't run until the coolant gets above the low temp setting of the switch.

[ninetyseven1]

I don't Know Jim
, but ever since this incident whenever I turn the key on the fuse 7 blows immediately and if I use a 30 amp fuse in f7 then the fan comes on by itself when the key is turned on and it goes on high

[JimLev]

Replace the relay, the contacts are probably welded together for drawing too much current.

[computiNATEor]

[ninetyseven1]

Replace the relay, the contacts are probably welded together for drawing too much current.

What relay? the low speed one or high speed? the low speed one has been swapped out 3 times with no changes for the better.

[JimLev]

Yes, the low speed. That's the relay that F7 supplies power too that you have connected directly to the fan motor when you bypassed the two resistors.
If you pull the low speed relay out does the fan still run??
If it doesn't then put the relay back in and unplug the temp connector on the side of the radiator. Does the fan still run?

I'm trying to help you but you don't answer the questions I'm asking you. It's time for some answers otherwise I'm done.
It took 31 post to find out you had bypassed both resistors because they were blown.

[ninetyseven1]

Yes, the low speed. That's the relay that F7 supplies power too that you have connected directly to the fan motor when you bypassed the two resistors.
If you pull the low speed relay out does the fan still run??
If it doesn't then put the relay back in and unplug the temp connector on the side of the radiator. Does the fan still run?

I'm trying to help you but you don't answer the questions I'm asking you. It's time for some answers otherwise I'm done.
It took 31 post to find out you had bypassed both resistors because they were blown.

If i pull the low speed relay , then no the fan wont run. If i unplug the temp sensor then yes it still runs.

[JimLev]

Ok, so the fan is getting power thru the relay all the time. Then either the wiring to control the relay coil is screwed up which is keeping the relay energized all the time or the HVAC panel is keeping the relay energized like Mikyzz4 suggested a while ago.
So next would be to unplug the HVAC panel to see if the fan stops.

[ninetyseven1]

Ok, so the fan is getting power thru the relay all the time. Then either the wiring to control the relay coil is screwed up which is keeping the relay energized all the time or the HVAC panel is keeping the relay energized like Mikyzz4 suggested a while ago.
So next would be to unplug the HVAC panel to see if the fan stops.

ok will do Jim, so your saying to pull the big main power harness out of the HVAC unit then right? and also should i install both my brand new resistors during this test process or do i risk blowing them again?

[JimLev]

Big main power harness??
The HVAC panel in the center of the dash above the cup holders, only has 2 small connectors on the back side. Unplug them both.
Resistors don't need to be installed for this test.

[philly98540]

Bless you Jim.

[computiNATEor]

^ +1,000,000

[computiNATEor]

ok will do Jim, so your saying to pull the big main power harness out of the HVAC unit then right? and also should i install both my brand new resistors during this test process or do i risk blowing them again?

No, just disconnect the HVAC controls inside the car just below the radio. There are two connections on it, but the HVAC controls dictate how the entire HVAC system operates, including turning the auxiliary fan on or off.

[JimLev]

So ninetyseven1, what's the deal. A ton of posts and PM's and then you disappear.
What did you find out, the HVAC panel was the problem?????

[BimmrMeUpSnotty]

LMA OFF!!! Some people should know their limitations and bring the hacked up car to the shop...Poor E39...