Heater temp knob adjustment?

[imjusthere]

I can only get heat if I turn the temperature knob all the way to its max. Then it's hot as hell and if I move it even slightly lower it goes completely cold again. Is there a way to adjust the knob? Any ideas what could be causing this?

[reelizmpro]

Did you do any work to the cooling system/heater hoses, etc. prior to the problem?

[Das Delfin]

I actually just realized this same thing:

it's supposed to be like that

the way it works is pretty cool. If you turn the knob all the way to blue, it's just total outside air with no heat at all. If you turn the knob all the way to hot you get 100% hot out of all the vents. The key word is all.

BMW was pretty cool with their HVAC. Not only do you have complete control of which air goes where in the form of three different vent sliders as well as valves on each mid-level vent, they also built in an automatic climate control feature.

The round vent-looking thing above the temp knob is a sensor for the HVAC which determines the in-cabin air temp. The HVAC system then uses this figure, as well as where you place the knob (as long as it's not all the way blue or all the way red) to produce a temperature associated with the placement of the temp knob.

Most of our cars have merely two blue and red lines which intersect and don't display any kind of numerical temperature setting. But some cars do. And it's easier to guess what temperature you're setting the car to be at. But in the grand scheme of things it's not hard. Do you want it hot, cold, or somewhere in between?

Anyway it figures out how hot you want it to be and makes it that hot.

BUT!

They go one step further. BMW designed a system which, while the temp knob was in the middle section (so not 100% hot and not 100% cold) it would send warm air (depending on the setting of the knob) to the floor and the windshield vents, but cool air to the hand vents. This was so the driver could keep the cabin warm, but direct cooler air at his face to keep him aware. It's really cool.

The solution is to use any of the million vent controls to turn off or lower or direct away the cool air going to your face. So set the temp dial where you want and turn off the mid vents.

So to recap at full cold all vents will be cold. And full hot all vents will be hot. At anything in between the mid vents will be outside temp while the floor and windshield vents will be warmer to adjust for the temp set by the dial.

[JasonC]

Very few e30s had a sensor above the temp knob. Most of them have that little vent looking thing there, but there is nothing behind it.

[george graves]

Jason is correct. Almost none of the e30's have any sort of intelligent temp control with a sensor. (by none, I mean less then 1%)

The system is 100% mechanical. It seems as if they planed to build some electronic control but didn't get to it. You have to remember back in the 80/90's it took about 7-10 years to design a car, and build all the tooling to make it. So shortly after the e30 was released, they were already on to the e36. (now I think it's down to 2-3 years)

All HVAC panels have that little sensor thing(that I know of). As far as cool air on the center vents and hot on defost and feet, mine doesn't do that.

Someone correct me if I'm wrong, but the temp control is actually a mix knob. Of "full heat", all the air goes through the heater core, and on "full cold", none of it does.

The "only hot" or "only cold" issue OP is reporting could be a few things. Off the top of my head I would think an air bubble or poorly blead cooling system. That or a mechanical problem with the knob and it's associated lever and/or it's push/pull tubes that lead to the air valves.

[Das Delfin]

check pages 27 and 28 of your owners manual if you want to read the bmw script

[Das Delfin]

To follow up, the system is not 100% mechanical. When the temp control is on full cold there is an electronic valve that shuts off water flow to the heater core. The recirc controls are also electric.

When the temp control isn't on full cold there is a cable controlling an air flap between the evaporator and the heater core.

So while yes you could have a problem, what you want to do is check for normal operation before trying to track down a problem that isn't there. Put your temp control at 3 o'clock or 12 o'clock and stick your hand on the defrost vents or the floor vents and see if you feel warm air. Because like I said (unless your dash was taken apart and not put back together properly) it's designed to work that way.

[george graves]

^Oh yea. Forgot about those little motors. They also go bad and lock up.

[Das Delfin]

yeah. I thought mine was broken for the longest time. But then I learned that it wasn't and the car was designed a certain way. Saved me a lot of time taking apart the heater box looking for problems that weren't there.

[jeffnhiscars]

The recirc button just operates 2 small servos motor that move a pair of flaps which either allow fresh air in or not. It's an all or nothing flap. The temp knob is 100% mechanical as it just operates a "blend door" that directs air either thru the heater core or evaporator OR an infinite range of options from 0-100%. That, for instance, also allows you to run the AC while heating which is how you dehumidify in winter if you live in a cold damp climate (also in the owners manual)

The only part of the AC that's even remotely electronic is the evaporator sensor which will (or should) shut off the compressor at 37 degrees.

[imjusthere]

So I tested this again as recommended. I get a slight temperature variation between 0 and 90% on the temperature knob. Maybe just a couple of degrees. Then a huge temperature range from 90 to 100% on the temp knob. Is this just normal e30 behaviour? I don't remember it being this way and it seems like odd behaviour anyway. To answer some questions, the heater core was replaced and the dash was removed by the last place that worked on it when they removed the engine.

Sent from my XT1254 using Tapatalk

[reelizmpro]

So I tested this again as recommended. I get a slight temperature variation between 0 and 90% on the temperature knob. Maybe just a couple of degrees. Then a huge temperature range from 90 to 100% on the temp knob. Is this just normal e30 behaviour? I don't remember it being this way and it seems like odd behaviour anyway. To answer some questions, the heater core was replaced and the dash was removed by the last place that worked on it when they removed the engine.

Sent from my XT1254 using Tapatalk

That's the answer I was looking for. They probably switched the inlet and outlet hoses at the firewall. I did that once and got the same result you're describing. It's easy to mix them up so first verify that the hoses are correct. The hose from the head goes to the bottom pipe (inlet).

The other possibility is when they pulled the dash/climate control panel they misadjusted or didn't secure the air mix bowden cable. I've done that also.

http://www.r3vlimited.com/board/showthread.php?t=203038

[imjusthere]

The hoses appear to be correct. The top one goes to the thermostat housing.

Sent from my XT1254 using Tapatalk

[Das Delfin]

the temp dial pulls a cable which opens a flap allowing air into the heater core. If you feel resistance in the temp dial then the cable is most likely connected and working properly

turn your temp dial to 3 o clock and stick your hand on the defrost vents once the car has warmed up. Not the mid vents - the defrost vents

[imjusthere]

The temperature dial has very little resistance but it feels the same throughout the whole range. I definitely get warmer air out of the defrost vents than I do out of the face vents. I guess I'm going to chalk this up to normal e30 behavior even though I don't remember it being like that before. It sounds like the alternative is to remove the dash which I'm not excited about.