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Discussion Starter · #1 ·
Have a HVAC problem with my 2005 E46. Dash, floor, or defrost vents were always blowing heat in the last 3-4 months (during summer or winter), unless A/C turned on. With A/C turned on, and face-level vents selected in Summer, I can get A/C cold air from vents. With A/C off, vents blow HOT. This is NOT a center vent "setting" issue. I know to select the blue or red dots depending on what temp I want the center face-level vents to blow.

It's currently winter, so having heat all the time, wasn't a problem - I would adjust fan speed to find a comfortable temp. However, 2 days ago, the heat stopped blowing, and all I get is ambient (cold) air from all vents (floor, face, or defrost) vents. The A/C is off and not running, it is just cold outside air coming in.

Doesn't matter what temp I set the controls to (59 deg - 91 deg) - always blows cold (last week, was always blowing hot no matter what temp it was set to). Doesn't matter if I have it on "Auto Temp Control" or "manual", and doesn't matter if I have it on "Auto Recirculate or Manual Recirculate". Always blows cold now. I have absolutely no heat coming into interior.

Car runs at steady 90 deg C, temp guage right in middle. Replaced radiator, thermostat, hoses, expansion tank a year ago and flushed cooling system. It is NOT a coolant bleeding issue.

Assuming it must be outside air sensor, inside temp sensor, or defective water valve. Is there any way to check operation of inside temp sensor without special equipment or software? All I have is std. OBD2 tool - haven't checked to see if it can read outside air temp yet.

- where is inside air temp sensor?
- where exactly is outside air temp sensor?

I know there are a ton of posts about this. . . . but haven't seen anyone with this same problem - always blowing hot. . . then NO heat. Assume that helps diagnose the problem or helps ID the problem part? Any guidance or suggestions would be appreciated. Thanks!
 

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Sounds like a wonky heater control valve. Right under the intake elbow, behind the airbox. Super easy to replace.
 

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Sounds like a wonky heater control valve. Right under the intake elbow, behind the airbox. Super easy to replace.


Would this fix my issue? In both my e46’s, it has always felt that I would need the AC to get ambient air temp in. I just always assumed it was just an E46 thing, like heat from the engine just coming in, but it’s really frustrating


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Would this fix my issue? In both my e46’s, it has always felt that I would need the AC to get ambient air temp in. I just always assumed it was just an E46 thing, like heat from the engine just coming in, but it’s really frustrating
Possibly. My symptoms were:
  • A/C would blow warm (air was demoisturized so I knew the A/C was actually working---besides being properly charged) from time to time. Usually after a hot start when running errands.
  • Heater would occasionally blow max heat even when set to a lower temp like 68 or 70. Like, my feet would inexplicably get REALLY warm.
Replacing the heater control valve fixed both issues.
 

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How important is it for replacement heater control valve to be a genuine BMW part? There are cheaper aftermarket valves available.
 

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Possibly. My symptoms were:

  • A/C would blow warm (air was demoisturized so I knew the A/C was actually working---besides being properly charged) from time to time. Usually after a hot start when running errands.
  • Heater would occasionally blow max heat even when set to a lower temp like 68 or 70. Like, my feet would inexplicably get REALLY warm.

Replacing the heater control valve fixed both issues.


That second one sounds like my issue. Sad coolant needs to be drained, but would so be worth it. Probably will set it aside for the summer
 

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That second one sounds like my issue. Sad coolant needs to be drained, but would so be worth it. Probably will set it aside for the summer
:shhh: I didn't drain my coolant. ;) The replacement heater control valve comes with plastic caps over the ports that you can use as you move the hoses one-by-one. I put a catch pan underneath the car and lost maybe a few cups of coolant. Topped it off and all's been peachy for the past 3 months.
 

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:shhh: I didn't drain my coolant. ;) The replacement heater control valve comes with plastic caps over the ports that you can use as you move the hoses one-by-one. I put a catch pan underneath the car and lost maybe a few cups of coolant. Topped it off and all's been peachy for the past 3 months.


Now that is some erotic car literature
 

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Interior temp sensor is in the panel behind the little grill. There is a small fan/blower visible from the back side that draws air through the front over the sensor. The grill, blower and passage get clogged up with dust and dirt over time. Blowing out with compressed air will clear out the buildup. You need bmw specific diagnostic program or scanner to be able to see what the sensor is reading. Cleaning it is good maintenance and I recommend doing this. Your problem seems like a stuck open heater valve though. Remember that the heater valve is normally open (spring) and powered closed so if it is disconnected or not being electrically operated for any reason, it will remain in the open position (full heat) no matter what setting.

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Discussion Starter · #11 ·
Had full heat the last 3 months, now there is no heat. Tried disconnecting plug to HCV tonight, but still no heat. Not sure if stuck in closed position now. One water line to heater core hot, the other cold. Didn't seem to be getting 12V to connector, but need to try smaller probes on my voltmeter and double-check.
 

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Discussion Starter · #12 ·
Just blew compressed air into both vents on climate control panel. Didn't seem dirty or dusty at all, but figured, it can't hurt. Will check operation on drive to work in morning.
 

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Discussion Starter · #13 ·
FYI - outside temp probe seems to be working OK - proper outside temp reading on dash/display.
 

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Don't force anything into the connector. The terminals are small and if you spread them you will have connection issues. You can plug in another valve without connecting the hoses and see if it opens and closes properly. You can also replace the current heater valve with a hose connector bypassing it. Should have full heat then. If not, your cooling system is not bled properly or the heater core is plugged and needs to be flushed. You have checked the coolant level right?

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Discussion Starter · #15 ·
Thanks. Was going to probe terminals from the top "wire" side, but needed skinnier probes, which I have on another voltmeter.

Yes, coolant level is OK. Heater core flushed last year and all new coolant last year.
 

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Discussion Starter · #16 ·
Checked small fan behind interior climate control panel - cleaned all dust from fan blades and sensor. Was spinning just fine. Checked all connectors - plugged/unplugged to be sure.

Ordered new heater control valve - waiting for it to arrive. Weather getting cold again - might take old one apart today and gut it so I get constant heat at least for now??
 
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