Blower Motor/Resistor Issues

**Bordom** · 08-23-2015 10:42 PM

Vehicle: 1996 2.8 12v A4 QM

Issue: Blower motor does not turn on with inputs from the Climate Control headunit (CCH). CCH registers that it is showing fan speed on the LCD screen and it responds to all commands. Blend doors etc can all be heard moving, as well as hearing the AC compressor turn on and up the engine idle.

The blower motor will work sporadically if I hit a big enough pothole. Reading up on this, it seems that the resistor that controls the blower motor may be fried and causing my issue.

I originally replaced a FEBI unit in the car with another known working unit from a pnp (pick'n pull) 96. Tested it before it went in and it seemed to work fine.

A few days later, I hit a bump in the road with the fan on med-high settings and the blower motor quit on me again. This was a few weeks ago.

Yesterday I hit a rather large pothole and the fan roared to life at full blast. Pulled over, looked for obvious damage from the pothole, and got back in the car. Shut it down and restarted to see if the fan would work, and it did.

Drove it to my destination and parked the car. Came back to continue driving and the fan was again dead.

I'm thinking this is a resistor fault, but I want to clarify with knowledgeable people. In looking for a possible replacement, it seems as though resistors are only available for 97+ model years.

A DIY fix may be in the works with this if it is indeed the resistor

**down_n_dapper** · 08-24-2015 03:54 AM

had the same issue on an E46 ( i know its not the same but it was a 2001 and had same issue) fan was ultra sporadic, woul work one second, go crazy the next and sometimes not turn on, had a mind of its own. replaced the resistor with oem unit and it was good as new. I'd be betting its the resistor again, might not be connector 100% but a replacement should handle it.

are you unsure if the 97+ resistor is the same as your 96?

**Bordom** · 08-24-2015 04:50 AM

I have yet to check if they are the same. I think it may be the same as the 90 seeing as it used the 90 blower motor

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**bhusted** · 08-24-2015 07:35 AM

To be clear, there is not a "resistor" that controls fan speed. To control fan speed the voltage is chopped by a transistor as in a PWM circuit. To protect from power spikes, the circuit is current limited.

I've fixed problems like this twice now by replacing the blower motor itself. As the bearings and brushes in the blower motor age, more power is required to run the fan. Eventually the current required exceeds the set limits and the circuit is shutdown to protect itself.

**Bordom** · 08-24-2015 09:28 AM

So then the items listed on ECS that "control fan speed" are not resistors but circuits?

I've found only these and nothing for pre-97
http://www.ecstuning.com/Audi-B5_A4-...cal/ES2143386/

These are from the 90 series which I think carried over to the first B5s.
http://www.ecstuning.com/Audi-90-Qua...cal/ES2525007/

I will be disassembling the glove box area to locate either of these today

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**seanf86** · 08-25-2015 06:34 AM

see if thats what you need

**bhusted** · 08-25-2015 07:06 AM

Originally Posted by Bordom

So then the items listed on ECS that "control fan speed" are not resistors but circuits?

I've found only these and nothing for pre-97
http://www.ecstuning.com/Audi-B5_A4-...cal/ES2143386/

These are from the 90 series which I think carried over to the first B5s.
http://www.ecstuning.com/Audi-90-Qua...cal/ES2525007/

I will be disassembling the glove box area to locate either of these today

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Just because ECS calls it a resistor does not make it so. The unit from the 90 series does appear to be the more traditional resistor with maybe 4 or 5 speeds.

**Bordom** · 08-25-2015 07:11 AM

Originally Posted by seanf86

see if thats what you need

So I basically gotta pull the dash for that thing? God damn.

Anyways, I solved my issue. On 96' the blower motors came with 2 pin connector type blower motors where 97+ came with 6 pin that was used throughout the model generation.

Upon dismantling everything, I found one of the connectors had melted into the rubber

There was also some play with the male end of the connector that would cut power to the blower if pushed too far some directions

I cleared the rubber out of the melted connector and re-attached it correctly instead of to the flat side of the female connector. Testing showed it now works without issue and I now have proper HVAC that is no longer a safety concern

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