ok so took my car on her first "road trip" to nashville (about 250 miles from atlanta) this weekend. everything was fine except for the air vent issue. i have both passenger and driver side temp settings set to cold, but once in awhile, the driver side would be blowing hot air while the passenger vent would be blowing cool air...and there is a big difference between the air temp. eventually i just kept it closed b/c otherwise it gets really hot in the car. it seems to happen after driving for a while, would go away, and then do the same thing again. and it doesn't seem to matter whether the AC was on or not.

any idea where to start with this?

Heater control valve... located on the firewall. It is a dual valve system designed to cut off the flow of coolant to your heater core when A/C is on or heat is off. One of the valves is likely failing. Electrically controlled...coolant leaks into them and they stop working. Sometimes you will smell antifreeze also. Not a cheap part but then is anything on a BMW?
Item 15 in the image below

http://bmwfans.info/original/images/8619_p.png

http://bmwfans.info/original/E34/Lim/535i-M30/JAP/L/A/1989/07/mg-64/%5D%5Bimg%5Dhttp://bmwfans.info/original/images/8619_p.png

http://forums.bimmerforums.com/forum/%5Burl=http://bmwfans.info/original/E34/Lim/535i-M30/JAP/L/A/1989/07/mg-64/%5D%5Bimg%5Dhttp://bmwfans.info/original/images/8619_p.png%5B/img%5D%5B/url%5D

Sorry to butt in... but could this be why it seems my hot air isn't very hot comming from the vents..?

Have you tried rolling the center dial on the front center vents to cold?

Heater control valve... located on the firewall. It is a dual valve system designed to cut off the flow of coolant to your heater core when A/C is on or heat is off. One of the valves is likely failing. Electrically controlled...coolant leaks into them and they stop working. Sometimes you will smell antifreeze also. Not a cheap part but then is anything on a BMW?
Item 15 in the image below
http://forums.bimmerforums.com/forum/%5Burl=http://bmwfans.info/original/E34/Lim/535i-M30/JAP/L/A/1989/07/mg-64/%5D%5Bimg%5Dhttp://bmwfans.info/original/images/8619_p.png%5B/img%5D%5B/url%5D
is there something i can look at before spending money on the control valve.

Have you tried rolling the center dial on the front center vents to cold?
yeah its on cold. does the center dial control both the passenger and driver center vents?

yeah its on cold. does the center dial control both the passenger and driver center vents?

Just to make sure, Im not talking about the dial near the OBC.

I had to turn on the heat for the first time the other day and the dial seamed to control, not only the center vents, but also the vents on the doors.

is there something i can look at before spending money on the control valve.


You can test them if you are electrically inclined. Somewhere here is a thread on it but essentially you disconnect the connector and apply 12V (or ground) and you can hear them close (or open, I forget)

Gee confused.....just general troubleshooting practice.:)

The dial on the ctr vent...controls the air temp of all of the dash vents (even the ones on the door). The diagram below shows the air distribution note how all of the vents along the dash are half-n-half...they receive warm and fresh air:

BTW....remember to close the vent at the rear of the ctr console during winter as not to freeze the rear passengers out with all that cold air from outside blowing on them. If they get to warm in the back, then they can open that vent to "cool" themselves down without you having to adjust the HVAC settings. ;)

http://memimage.cardomain.net/member_images/7/web/739000-739999/739005_8_full.jpg