Quote:
Originally Posted by tboar
Hey, I see several folks have had this issue, so I'm going to share my experience with it. My car (F10 550i) started dumping huge amounts of heat into the drivers side footwell, but all the vents and the passenger footwell received cold air. BMW master tech said to have the system recharged, then if it persisted, bring it in. It persisted. I brought it in, ended up paying for 5 hours of diagnostics and a new heater valve. Two days later, the problem was back. Car went back to the dealer and they did a few more things diagnostically, put in new software, gave it back. Problem showed up on the drive home. So what I did was the following...
1. Electrically disconnect the heater valve (you might need to pull the cross brace and driver's side engine air intake to get there). Then I took it for a drive, AC on, set to vents and floor, both sides at 60 deg. Result, both footwells got extremely hot air. This means the valve defaults to the open position.
2. Multimeter time. With AC set to max, the voltage on two of the three pins of the valve connector went to 12V. Obviously, the third then is ground. AC off, heat set to max... Both pins were approximately 9V. Then I tested the valve side of the connector. Both coils measured 22 ohms to ground, and 44 ohms when both are in series. This means there's a signal being sent and there's neither a short or open circuit. In other words, the valves should both respond.
3. Quick control system check. Set one side to 60 and the other to max heat. I got 12V one one pin and 9V on the other. Change which side is set to 60/max heat and the 12V/9V should switch as well. It did.
4. Reconnect the harness to the valves. Set AC to max, check for magnetism on the coil. One had it, one did not. The further rearward one was the one that did not energize. You can generally test coils with a thin piece of metal (like a feeler gauge) by holding it to the top of a coil. If the coil is energized, the metal should be drawn towards it.
Conclusion... Signal is reaching one side of the connector, the coils are electrically fine, yet one valve is not responding. Hence, one pin of the connector isn't connecting. The bad news is that this connector is not commonly available, but can be bought for about $18 from BMW and it solved my problem immediately.
Moral of the story... At the end of the day, you might need someone with a $4000 diagnostic scan tool, or you might not. Underneath all the complex CAN, networks of sensors, actuators, and controllers, there are still basic mechanical components whose issues than can often be diagnosed with simple processes and tools. Check the obvious stuff first!
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May i ask for that sensor part number ? Thanks