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      11-30-2018, 01:08 PM   #1
fixherz4
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03' BMW Z4 with No hot from heater

Car: 2003 BMW Z4 2.5i with no warm/hot air blowing through heater, only cold air. The Z4 has Automatic Heat & AC with temp gauge on knob.

There is no Hot air being blown. The heater/AC Fan blows as expected. Adjustment for directional air to upper, middle and lower works as expected except on cold air. Engine heats up properly, temperature gauge working correctly. Turning thermostat to highest doesn't make a difference.

Issue started when the coolant overflow box was replaced. Replaced unit due to crack in overflow box. Flushed system at time Multiple times. Coolant wasn't dirty at the time of flushing.

Question: does the thermostat direct hot water to heater core or is it automatically pushed/sent through the core ? Is there mechanism which precludes hot water to travel through heater core?

I am about to replace the Automatic Heater/AC unit.

I repair the car myself when possible.

Suggestions.
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      11-30-2018, 01:36 PM   #2
StickMon
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Want some of my hot air?
I have the exact opposite problem. Back in August I got stuck on full hot.
Everything else works, but I can't hear the blend flap actuator.
Not sure if actuator failed, controller failed, or temp sensor failed.
Maybe the temp sensor failed and the car thinks it's absolute zero.

But back to you:
I think water flows through the core at all times, and temp is controlled by the blend flap.
If you turn the car on, but don't start it, and stick your head under the glove box, you should be able to hear little gears whizzing when you move the controls.
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Last edited by StickMon; 11-30-2018 at 01:50 PM..
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      12-04-2018, 10:44 AM   #3
fixherz4
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Thanks for the update. I'll try that when I get a chance. I didn't want to pull out the air vent and radio just to replace automatic heat/AC control unit if it wasn't malfunctioning. That would make sense, the AC seems to be working fine when the AC is initiated (push on) and temp thermostat turned to cold (hard to tell when the ambient temperature is 35degrees.
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      01-20-2019, 09:03 PM   #4
TXBMRMAN19
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You might want to try flushing the heater core in case you have air trapped in there. Have you done any work to your cooling system lately?
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