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5-Series (E12,E28, E34, E39, E60) Chat relating to the BMW 5-Series of all generations. Specific models include: BMW 518, BMW 520, BMW 520i, BMW 530i, BMW 528i, BMW 530i, BMW 518i, BMW 524d, BMW 525i, BMW 525e, BMW 528e, BMW 540i, BMW 535i, BMW 520d, BMW 525td, BMW 525d, BMW 530d, BMW 525i/xi, BMW 530i/xi. (BMW 5-Series Forum)

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Old 07-03-2005, 08:34 AM   #1 (permalink)
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Bmmf40 is an unknown quantity at this point
1989 E34 535iSE Manual. 248K miles.

Has anyone any ideas on this fault:

Heater blows hot air all the time unless fan is switched off on the heater controls. I then can't get any cold air so I cook in the car! Doesn't matter what settings you select on any of the controls, it stays hot.

Have replaced the Heater control panel, model is the automatic version with seperate left\right edge controls and loads of push buttons.

Heater valves replaced.

Has spent hours hooked up to the BMW diagnostic system at my dealer and they cannot find the faults.

If I isolate the heater valve electrical supply on the valves themselves and feed 12v direct from another source then they switch off OK and the heater core goes cold. Wiring to the valves has been checked using the BMW diagnostic system and is OK.

On the verge of total hair loss over this................ ghead
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Old 07-03-2005, 11:38 PM   #2 (permalink)
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If I isolate the heater valve electrical supply on the valves themselves and feed 12v direct from another source then they switch off OK and the heater core goes cold. Wiring to the valves has been checked using the BMW diagnostic system and is OK.
Well if you supply power to the heater valves and the system goes cold then obviously the system/wiring was NOT checked correctly using the BMW diagnostic system.

The heater valves are powered closed meaning that they should have a constant power and ground present unless the heater is turned on, then the power or gound is taken away (I think ground) and the valve opens because it is built to be sprung open anytime there is no signal present (safety feature)

Sounds like you may want to take it back to whoever you paid to diagnose it and have then recheck it (should probably be free) since you did pay them to diagnose the problem and it sounds like they overlooked this.

Good luck,

DT
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