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AUX Fan not working

 
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geminiys



Joined: 13 Oct 2004
Posts: 182
Location: SF, California

PostPosted: Sat May 11, 2013 1:01 pm    Post subject: AUX Fan not working Reply with quote

My AUX Fan is not turning on when AC is engaged. Before I attack fixing it I would like to know all possible things I need to check before purchasing them all.
Which relay in the fuse box is responsible for engaging the FAN when AC button pressed (Purple or Yellow and which yellow one) and how to check if relay is the problem? Could the problem be my Final Stage Resistor pack? The entire AUX Fan assembly is about 2 years old. It was replaced after I hit a wooden box on the freeway and cracked it. I will have to check if it still works by applying 12V to the socket but I want to see if there is anything else that can be causing it not to work.
The car is BMW 328is, 1997 and it has 290k on it.
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PJK



Joined: 14 Feb 2002
Posts: 1829
Location: Shingle Springs, CA

PostPosted: Thu May 16, 2013 2:05 pm    Post subject: Re: AUX Fan not working Reply with quote

I'll try to make time to study the Bentley in order to sort this out. It is not the final stage. That controls the HVAC blower. I'm pretty sure the aux fan is controlled by an electromechanical relay in e36s. It is a solid state "final stage" like box in an e46.

Phil

geminiys wrote:
My AUX Fan is not turning on when AC is engaged. Before I attack fixing it I would like to know all possible things I need to check before purchasing them all.
Which relay in the fuse box is responsible for engaging the FAN when AC button pressed (Purple or Yellow and which yellow one) and how to check if relay is the problem? Could the problem be my Final Stage Resistor pack? The entire AUX Fan assembly is about 2 years old. It was replaced after I hit a wooden box on the freeway and cracked it. I will have to check if it still works by applying 12V to the socket but I want to see if there is anything else that can be causing it not to work.
The car is BMW 328is, 1997 and it has 290k on it.
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PJK



Joined: 14 Feb 2002
Posts: 1829
Location: Shingle Springs, CA

PostPosted: Fri May 17, 2013 1:32 pm    Post subject: Reply with quote

Bentley shows in addition to the fan motor(s) fuse 16, fuse41, a double temperature switch on the radiator, a pressure switch (on the AC system?), a low speed relay , and a high speed relay. The fan motor is shown as two motors in Bentley but I'm not sure I believe that. The relays can be closed by the temp switch, the pressure switch. or the DME. I'm guessing the temp switch is not the problem since the fan does not come on with the AC.

The relays are in the power distribution box near the brake booster. The relays shown are in the row closest to the fender and are the rear relay and third from the rear. Page 170-5 in Bentley.

Phil
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geminiys



Joined: 13 Oct 2004
Posts: 182
Location: SF, California

PostPosted: Fri May 17, 2013 1:48 pm    Post subject: Reply with quote

Thanks PJK for looking into it.
I looked at the Bentley manual as well and saw exactly what you did. I went into my car and checked the relays. The Yellow color relay turns the AC Compressor and one of the speeds. The Purple color one is related to another speed. Don't remember which one is which. To understand better, I am trying to see which relay out these 2 controls the AUX Fan when AC button is pressed in the cabin. I don't have any spares to try replacing it. All I did is removed the Yellow color relay while AC was running and it stopped the AC Compressor but Purple did nothing while in or out. I am suspecting the Purple color relay is the problem but not too sure.
I have checked all my fuses and they are fine.
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