[langsbr]

I thought my blower motor resistor gave out as I lost all blower speed. No matter what it was set on, there was no air movement. Ordered and installed a new resistor, and same issue - with an exception.

The blower works fine when the ignition is on, car not running. Never misses a beat.

Once I crank the engine, the blower slows until its stopped and then I have no air movement. No matter what I do, as long as the engine is running, the blower does not turn back on.

Stop the engine, ignition on, fan works like a champ.

I have ordered a new blower motor just in case its getting too much current and stopping, but I hate throwing parts at the car without any idea. I have yet to swap the old resistor back in to see if it works when the engine is not running (why would that normally be checked anyways).

There were no signs of any issues with the wiring - it looked perfect, not even any discoloration.

EDIT: Protools shows not a single code. I can adjust the fan speed to 50% and 80% and it responds properly when the engine is not running, no effect when running.

[gbalthrop]

Please post Last-7 Characters of your VIN, so we can provide correct wiring for your car, and suggest TESTS (you will need DMM/ Multimeter).
George

[langsbr]

Originally Posted by gbalthrop

Please post Last-7 Characters of your VIN, so we can provide correct wiring for your car, and suggest TESTS (you will need DMM/ Multimeter).
George

The VIN is VF50105.

I have a multimeter and can test. I guess the confusing part is that the blower motor is clearly receiving power when the engine is not running, but then slows and stops when the engine is running. Would a multimeter not simply confirm that it is receiving voltage in one condition and not another?

The fan doesn't immediately quit when starting the car - it continues for a bit, then begins to slow, and eventually stops completely.

Even the hvac control module wouldn't make sense in that scenario to me since the blower is responding properly to commands while engine off, it's correctly sending the command.

I was thinking possibly the fan is just not able to handle the load from the charging 14V rather than 12v battery only - but boy that sure seems sensitive.

[dave4]

I had a similar issue with my blower motor a couple years ago. While driving, I had low setting and high setting. Nothing in between, no matter what I set the speed at. I installed a new blower and same issue. After researching more, someone mentioned to get a new battery. I did, and the issue was fixed. Prior to getting the new battery and registering it, I tested the old battery in INPA and it said it was fine.

How old is your battery?

[langsbr]

Battery is less than 3 years old. Here's where nothing makes sense.

I figured I needed to see if the original blower motor resistor had the same symptom of working when the car was not running, but not while running. I swapped the old resistor back in, and the blower motor works perfect the whole time now!

Swapped the new blower resistor back in and it only works while the car is not running. So, at least that part is defective, but how/why does everything work again? I saw no loose wires, there's nothing that has even the slightest bit of discoloration from heat or poor contact like many of the other blower wiring posts. Very strange scenario indeed, but everything is back to a proper working state now.

[gbalthrop]

Originally Posted by langsbr

... I lost all blower speed. No matter what it was set on, there was no air movement. Ordered and installed a new resistor, and same issue - with an exception. The blower works fine when the ignition is on, car not running. Never misses a beat. Once I crank the engine, the blower slows until its stopped and then I have no air movement. Stop the engine, ignition on, fan works like a champ...

Originally Posted by langsbr

... I swapped the old resistor back in, and the blower motor works perfect the whole time now! Swapped the new blower resistor back in and it only works while the car is not running. So, at least that part is defective, but how/why does everything work again?...

Wiring diagram, with "Line ID", Location diagrams & Connector Views are attached to NEXT Post, so as NOT to ruin margins here. Explanations below related to the Connector numbers (X18722 at Blower & X14272 at JBE) used in wiring diagram, and pin #s and wire colors are also as shown in diagrams.

Apparently the Electronics in the "Replacement Resistor" (Blower Output Stage -- N2 on wiring diagram) are defective. My guess is that when voltage supply via Red/Violet wire is in 12.5V range (engine off, Alternator NOT charging) the "Replacement Output Stage" works as intended. When engine is running and alternator charging, the System Voltage increases to ~ 14.5V, and apparently THAT creates issues with Blower Speed.

THREE (3) things are needed for blower function at a particular speed:
1) Primary Voltage Supply via the Red/Violet wire at X18722/2 or Socket #2 of Connector X18722 at the Resistor/ Blower Output Stage.

2) Chassis Ground at Brown wire, X18722/1.

3) PWM (Pulse Width Modulated) speed signal via White/Brown wire at X18722/4. Note that wire from IHKA Module passes through the JBE (A4010a) from X14272/18 to X14272/23.

If ANY of those 3 things is absent, the Blower will NOT function. So the tests would be:
1) Battery/ System Voltage at Red/Violet wire, X18722/2 (KL30, un-switched battery power) which should be ~ 12.5V engine OFF, and ~ 14.5 Engine ON.

2) Continuity to Chassis Ground (Near-0 Ohms resistance) between Brown wire, X18722/1 and good chassis ground.

3) Changing signal at White/Brown wire at X18722/4. I do NOT know the RANGE of proper signal, but it SHOULD change depending upon blower speed selected manually on IHKA Control Panel. Simple Volt meter reading can be done. If you have a meter that can read "Duty Cycle" or "Frequency", that might be more definitive.

My GUESS would be that the X18722 Connector had corrosion or other issue in the Pins or Sockets, and simply disconnecting several times restored proper connection. If the problem recurs, I would clean pins & sockets with Electronic Contact Cleaner, and examine for any loose sockets or pin damage, paying particular attention to the X18722 Speed Signal connection, as the low current flow there requires better connection quality. Pins/ Sockets #18 & #23 at the JBE Connector X14272 can ALSO be a factor.

Glad it's NOW working! Since "Seeing is believing" for most of us, the "UN-seen" is usually "UN-known". Wiring diagrams and Multimeters or other Electrical Tests, together with some ANALysis/ thought can at least offer some theoretical explanations for 'strange happenings'. Meter tests can confirm/ rule out various theories. Reference to wiring diagrams, and a few meter tests, BEFORE throwing parts, is usually a good idea.
George

[gbalthrop]

ISTA ScreenPrints of Blower Motor/ Blower Output Stage wiring diagram for 2007B 335i are attached.
George

[megusd]

Beleivd it or not, I had exactly the same problem on e87 118d LCI 2011
The fix is exactly the same:
Check power on regulator- OK
Check signal-unknown, oscilloscope didn’t pick up any pulses
Replaced regulator-works only with engine off
Read this post- decided to try
Replaced regulator to original - works
Got some beer to celebrate another win