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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Why no cabin heat?



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      07-21-2024, 08:42 PM   #1
Swamp Fox
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Why no cabin heat?

This has been a persistent problem for the last couple of years and I cannot narrow down where the issue is. The car is a 2013 E93 I owned since it was new and now has 147k miles on it. The issue is no heat in the cabin. The engine warms up okay, the A/C works, and the blower motor works and can be adjusted to blow air to the window, the middle vents, or below in the foot well. However, there is no heat but occasionally (but rarely) once the vehicle has been driven and warmed up randomly heat may come on and work fine. My thought is a plastic gear somewhere is stripped? Then I was thinking it was an actuator not opening the blend door. There are two actuators on the driver's side and three actuators on the passenger side. I can see the bottom actuator moving on the driver's side with an external armature and the middle actuator moving on the passenger side with an external armature when the heat is adjusted higher or lower. Which of the five actuators controls the blend door? Is it more likely to be either the control lever for the rear kinematics # 64116950996 or Rear Kinematics # 64116950994? Am I not thinking of something it could be? I am guessing other cars have had this same issue and are asking for your experience and expertise with the same issue. What part should I replace first? Is there a test I could do to narrow the problem to a specific part?
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      07-21-2024, 09:19 PM   #2
lowrydr310
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Do you have INPA? If so you can test and confirm the mixer positions.

Otherwise it's possible that you have a blocked heater core. I had this happen on an E90 325i. Flushed it both directions with water from a garden hose and it got the heat working again.
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      07-21-2024, 10:29 PM   #3
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Good idea! I have ISTA D/P from Rheingold but they went out of business and it is not working now and I cannot figure out why. I also have Autotel MX808S. I will check if it can do a position check.
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      08-16-2024, 09:11 PM   #4
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Several weeks later... I tested the mixer positions and they all pass. I also tested the inlet and outlet pipe temperatures to the heater coil on the left driver side. The inlet temp was 177 F degrees over the black insulations and 144 F degrees on the uninsulated pipe when the heat in the cabin was turned to 84 degrees. At the time I measured it was blowing hot air and everything appeared to be working well. However, this is an intermittent problem and by luck, it will reappear on a cold day. Could a mixer position be reading as though it is responding but this not be the case because of a stripped plastic gear? Where is the mixer position sensor getting its information from? From the actuator itself or is there a sensor on the mixer doors themselves? This is a perplexing issue chasing this gremlin. Which actuator controls the blend door for heat?
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Last edited by Swamp Fox; 08-17-2024 at 11:39 AM..
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