Heating not working correctly

[andynewton]

Hi, New to this forum so hopefully somebody knows about this and maybe some of what I mention might help others.  My E70 (2007) seems to have a mind of its own when it comes ot heating or climate control.  To get any heat I have to set the temp to full (28) on each side.. if I reduce to 27 it goes cool.. thats the first issue. But the weird one is if the passgener reduces theirs to say 24 the drivers side goes cold but when I reduce the drivers side only sometimes does the passenger side go cold. Now I have replaced the thermostat as engine would now reach above 73, and the EGR stat/valve..also replaced the heating control valve and had the air con re charged and cleaned.  I have no idea where to go on this one now.... I took the temp sensors from behind the vents out and tested them with hot water and they changed resistance so I assume they are ok... Really starting to pull out what hair I have left... so does anyone have any ideas please ... Thank you in advance

[Horizon]

There can be several causes, the most common is a blocked up probe grill or fan duct on the facia of the climate control unit, there is a ting grill which air is drawn into the unit, there is a temperature probe inside that tells the control unit if to heat or cool to keep the temp at the level chosen on the display.
If the air can't flow over the probe it gets confused.
Try blowing the vent out , with a low pressure blow gun, shine a torch in and see if the fans running.
Or it could be the Climate unit, or the heater valve block on the inner wing.
Try the grill/ fan first though
And welcome to the forum

[andynewton]

Hi thanks.. I did find the poll thing strange but it wanted those before I could post !!! Will know for next time.

Any way will take a look at this as I had the same thing on my old E53 ... but I didn't know if the E70 had the same so will take a look.

If its not that I might have to buy a new climate control IKHA module.....  I did replace the heating control valve on the inner wing...easy job , cost about 100 but didn't seem to work. 

So if this doesn't work ... is there anything else it could be do you think?  I was worried the heater core could be blocked ..

Thanks for the help

[Horizon]

The heater core won't be blocked.
Might have happened 30 years ago, modern coolants have an anti corrosion qualities, so you don't get the same corrosion and gunge build up these days.

[andynewton]

Thanks , I like your confidence, but I am sure you are right as it will get hot on both sides its more the control of that heat I think.... 

Going to remove IKHA tomorrow and check so I will let you know

Thank you very much for taking the time to reply

[andynewton]

Couldn't wait until tomorrow and a bit bored so took out IKHA earlier .. as suggested a bit dusty and the remains of an old insect.. so cleaned out the thin bar sensor and the small fan ... plugged back in and checked fan was running which it was...but still no good.

What seems strange is the fact that turning down drivers side effects /affects passenger side and visa versa ..not so much is air id directed to vents but very much when directed to floor

Tried swapping plugs on sensors in main dash vents, no good, tried swapping sensors over in vents ..still no good ... so now at a dead end ..I have no idea what this can be

If I turned down heating by just one degree both sides go cool...  Help !!! 

[Huxsta]

Well my 2p's worth is this. I had a similar problem yrs ago with my e39 530d and it turned out of all things to be fluff in the little air sensor on the front of the display. Hoovered it out and it cured the issue. Now I've just read your post and haven't bothered going to look at my e70 4.0d 2011 plate to even see if it has a similar little vent on the front like my old bus has. If it's the same you are looking for a little grill about the size of a small stamp!!!! Good luck anyway.

[andynewton]

Hi Thanks for the reply.  I have cleaned out the front sensor but still no good.  But I have got the BMW diag software so I plugged this in and it told me I have a sensor error, which I think is the right hand heater core sensor.

To check I cleared all the errors and used the car for a few days so tomorrow I will see if the error is in the memory again.  If it is then I should be able to find out which sensor.

Then the problem is ...how do I replace the heater core sensor... does this mean dash out... I hope not?

Anyone done this before?

[andynewton]

Ok so bit of an update.. I found how to use the INPA software and managed to check all of the heater/air circulation flaps are working fine. Also found the heater core sensors and they both report approx the same temp (1 degree off )  so all operations of the heating system check out ok... But i did find a repeat error in the logs which was for the AUC sensor, so going to replace that as its a 2 minute swap out and see what happens.

Interestingly the software showed up two other errors with the rear heated screen relay (which I cannot find for love nor money) and the passenger heated mirror faulty which I haven't looked at yet.. 

Will post again once I have replace the AUC sensor