Keeps the hot side cold and the cold side hot

[Sean H]

The wagon ('95 525i) has some funkiness with the climate control. The A/C seems to have developed a leak, as best I can tell. I get a can of parts store refrigerant down there, and it runs cool (not cold) for about a week or two, then back to the same. When i first picked it up back in October, it was full cold. Only change since then has been an aux. fan replacement. I'd like to give it a good, proper charge before switching parts, but if that doesn't do the trick, where are the usual suspects for these things? I was chasing ghosts on the 535 for awhile, and it ended up being the a/c line ports.
Now onto the heat: there ain't none. It's moderately warmer than fresh air, but nothing to write home about. I first noticed this yesterday, when it butt-cold outside, but the 535 handled it with no problem (of course, the 535 is an infinitely better car in very way, but still...). My gut is telling me that it's an aux. water pump, but I wanted to run it up the flagpole and see what the group thought.

[brosher]

Is the temp guage making it up to the middle? It should only take a few minutes to get up there. If it doesn't your thermostat could be stuck open, which would leave you with no hot air.

[Sean H]

Is the temp guage making it up to the middle? It should only take a few minutes to get up there. If it doesn't your thermostat could be stuck open, which would leave you with no hot air.

It's geeting up to temp in the normal fashion, so no luck there, I suppose.


The aux water pump function can only be recognized when engine runs in idle or low RPM. In such case the aux water pump ensures constant flow to the interior although the normal water pump runs at low speed. Some even kick out the aux water pump cpmpletely and heater works.

Measure the temperature sensors on each side and clean them, Bentley has the data. Or see here
it is from E32, but will help
http://bmwe32.masscom.net/johan/ihka/ihka.html

Ahhh... thank you. I will look into that.

[shogun]

The aux water pump function can only be recognized when engine runs in idle or low RPM. In such case the aux water pump ensures constant flow to the interior although the normal water pump runs at low speed. Some even kick out the aux water pump cpmpletely and heater works.

Measure the temperature sensors on each side and clean them, Bentley has the data. Or see here
it is from E32, but will help
http://bmwe32.masscom.net/johan/ihka/ihka.html

[shogun]

some more info
http://www.bimmerboard.com/forums/posts/220273/
http://www.bimmerboard.com/forums/posts/380566/
http://www.bimmerboard.com/forums/posts/402448/
http://www.bimmerboard.com/forums/posts/270285/
http://www.bimmerboard.com/forums/posts/171814/

[Ferret]

My Aux pump runs pretty much all the time... even with just the ignition on and the engine not running!?

[shogun]

Yes, that is correct. That is also a feature to use the rest of the heat of the engine cooling system to heat the interior after engine has been switched off.

[e34.535i.sport]

Is the temp guage making it up to the middle? It should only take a few minutes to get up there. If it doesn't your thermostat could be stuck open, which would leave you with no hot air.

Mine stays cool for a long time - temp reaches the mark before the middle and stays there when cruising at speed... If stuck in traffic it'll go to the middle is this a problem?

[whiskychaser]

Mine stays cool for a long time - temp reaches the mark before the middle and stays there when cruising at speed... If stuck in traffic it'll go to the middle is this a problem?
On the face of it your stat is stuck open and your fan clutch doesnt work properly:) Seriously, it may well be just a poor connection at the temp sender unit. But it would be wise to nail it down soon- any large variations in temp are cause for concern