My baby's too cold, my baby's too hot...

[RITmusic2k]

My baby's too cold
After taking part in the 19.7.00 diagnostic thread it's been determined that my thermostat seems to be stuck open; operating temperatures never get higher than about 85ºC as opposed to the 97ºC or so that it should be reaching. I'm already familiar with this issue and I think I know everything I need to know to handle it... I only bring it up because it let me make a clever thread title.

My baby's too hot
This is what I actually wanted to ask about: I rarely use the climate control system with A/C on. When I do turn A/C on everything is hunkey dorey and nicely cold.

But, when I go back to bypassing A/C and I just let the vent fan blow, lately I've been getting hot air out of the footwell and windshield defroster vents, even with the temperature set all the way down and the center vent dial turned to full blue. The air coming out of the main vents is just slightly warmer than ambient, and it gets hotter if I raise the temperature setting or turn the dial toward red. So, I have some control over the temperature of the main vents, but above and below seem stuck on 'hot'.

Is there a separate blend door that might be stuck, or what sort of condition do you guys think could cause something like this?

[Oli77]

I think what you describe is pretty normal. I too feel like just with just blowing air function (no AC), it is a tad warmer that outside.

Always thought it was that the path of the air intake for the system (through the cabin air filter) that contacts a bit of the motor heat.

How's your mpg?

[RITmusic2k]

It hasn't always been this way though - usually all the air coming out is at ambient+a little, but the defroster and footwell air is straight up hot.

As far as my mileage goes, I usually get ~25mpg tank average with 80% city driving, but I'm a bit of a hypermiler. I don't know if I should be getting higher than that, driving the way I do...

[telijah]

OK, let's get clarification on something... When you say bypass the A/C, are you turning the compressor off (snowflake button) or are you turning it from circulation to fresh air? If turning the compressor off, it is no longer attempting to keep the air "conditioned", and if you have is set to vent mode, it will just be drawing in outside air.

[RITmusic2k]

Correct, I'm deactivating A/C by pressing the snowflake button -

The air coming out of the vents is *hot*, even on a cool day - definitely not in the neighborhood of ambient temperatures.


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[llll1l1ll]

Either your heater valve maybe is stuck open or perhaps the air just feels hot because you've been blasted with cold air for so long.

[RITmusic2k]

Okay, so here's a line of inquiry I can pursue. Anyone have more info offhand on this heater valve?


... perhaps the air just feels hot because you've been blasted with cold air for so long. I think you misread me. I usually drive with A/C disengaged. I only put it on during the hottest of days; probably been used fewer than 20 times in the year-and-change I've had the car.


EDIT: within a minute of google searching I came upon an e46fanatics thread describing my exact problem, and I've got a part number for the replacement heater control valve. Thanks, llll1l1ll!

" Part number is 64118369805. They call it a "Hvac - Heater Control Valve". It is $59.80 from Tischer BMW. "

EDIT EDIT: after further reading, the heater control valve hasn't always been successful at resolving this issue when others have attempted the fix. Other points of interest are the function of the vent flaps behind the dashboard, and the status of fuse #62.

[llll1l1ll]

Heh well I hope I at least led you in the right direction! I'd check that fuse, if anything. Nothing is worse than spending a ton of money on other hard to fix things only to find out it was something really easy and cheap.

[RITmusic2k]

Update 6/2/12

Sure enough... fuse 62 was blown. While in the back of my mind that suggests there's still something wrong with a component for it to be drawing enough current to blow the fuse, sometimes fuses just blow. Not gonna take a test drive just yet, but I'll let you guys know whether that solved the A/C problem.

[Oli77]

Cool beans, slash slash slash slash one slash slash one slash slash!

[RITmusic2k]

Yep, that did it!


Went for a short errand, and with the new fuse, the air from the windshield/footwell/dash is now as cool as the outside air when my temps are set low.

Problem: hot air coming from windshield and footwell vents (dash vents slightly warm, but cooler than above & below), even with temperature set low.
Solution: Checked for blown fuse #62 (7.5 amp blade); replaced fuse with provided spare.

My baby's too hot: CASE CLOSED.