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Hi forum members I hope this hasn't been repeated. But I really have a strange problem

I have a 2001 318i se E46 and my issue is that I am getting hot air coming out of the the air vents on the front windscreen. When the climate control is on and at it's lowest of 18c I am only getting warm air but when I press the AC switch further down I get cold air coming out from the front vents but still warm air coming out from the front windscreen vents cancelling each other out??:ben:

Even with the ac unit off I get a trickle of hot air on the front windscreen vents:banghead:

I went to a back street garage that topped up the ac which didn't make any difference but mentioned that my air con control unit might be at fault and should be replaced as it should read 0 degress. But it's never been lower than 18 degrees. Could it be the unit?
 

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I read this in my owners manual, it's by design so you don't get condensation building up on the outside of the windscreen. AC will remove the humidity still

Sent from my PC36100 using Bimmer
 

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I currently have exactly the same problem with my 2001 BMW 318i. I have read several post on this forum but none of them seem to have a clear answer why this is and how to fix it.Did you ever get this problem fixed?
I changed the heater control valve but this did not fix the problem. I wonder if anybogy has a diagram for the air/ heating system.
 

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Sending cold air to the windshield (windscreen as you Brits call it) would actually defog the glass. That what my car does when I press the windshield defog button. What is the temperature of the air coming from the dash vents when the AC is off? Is it warm? If it is the heater control valve is suspect. It could also be an issue in the climate control module in the dash. You might want to spend the £ to have the IHKA (automatic climate control) or IHKM (manual climate control) scanned for errors. Find another bimmer (beemer for you Brits) owner who has INPA. This is BMW’s diagnostic software. Offer him (or her) a pint to scan the module.
 

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It is blowing hot air regardless whether the AC is on or off. All other dashboard vent are blowing normal/cold temp air. i not sure about the temperature but after 15-30 min driving, the car feels like a sauna.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Could be issues with the control unit. However if/when warm air is NOT requested (control unit functioning correctly) it powers up the heater control valve.
The valve is powered shut and all hot coolant is not allowed into the heater core.

You need to find out if the command to shit the valve is present?
If it is and hot coolant is still entering the heater core touch both (VERY HOT) coolant pipes in/out and if flowing AND the signal is present, the valve itself is bad.

By default, the hot water is always allowed entry, if the system suffers a complete failure. That's very typical German think for windscreen defrosting available at all times. Been that way for over 30 years.
 

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Could be issues with the control unit. However if/when warm air is NOT requested (control unit functioning correctly) it powers up the heater control valve.
The valve is powered shut and all hot coolant is not allowed into the heater core.

You need to find out if the command to shit the valve is present?
If it is and hot coolant is still entering the heater core touch both (VERY HOT) coolant pipes in/out and if flowing AND the signal is present, the valve itself is bad.

By default, the hot water is always allowed entry, if the system suffers a complete failure. That's very typical German think for windscreen defrosting available at all times. Been that way for over 30 years.
Thank you for your post. I will need to have a look at this. It seems the valve stays open. I was going to check if i could get the old valve to close by putting a voltage across the valve. In the mean time i also found a post that suggests it may be a simple as a fuse that i need to replace. unfortunately. I will only be able to check this in 2 1/2 when i will be back home. I am hopeful it is a fuse.
 

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2004 330Ci 85k miles
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It seems the valve stays open. I was going to check if i could get the old valve to close by putting a voltage across the valve.
The heater valve is normally open, via an internal spring, when unpowered. The controlling voltage is PWM (pulse width modulated) I believe to achieve varying degrees of opening. Applying 12V should slam it shut as a bench test.

Wiring Diagram

Heater Control Valve
 

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I have a similar issue with my 2005 330i. Hot air blows through the defrost vents, regardless of how the HVAC controls are set and the temp wheel between the center dash air vents is adjusted.

Examples:

Action: I set the HVAC to blow on the floor only, set the temp to its coldest setting, adjust the temp wheel to fully cold, turn on the A/C compressor by pressing the AC button.

Result: Very cold air blows on my feet, no air blows through the dash vents, side or middle, hot air, at lower velocity than the floor vents, comes of out the windscreen/defrost vents (vehicle is in motion). Same settings, vehicle not in motion, very little hot air comes out of the windscreen/defrost vents but there is definitely hot air venting out of the windscree vents, lots of cold air on the feet.

Action: I set the HVAC to blow on the floor, dash vents, and windscreen/defrost vents (i.e. all 3 vent selection lights are lit), set the temp to its lowest setting, adjust the temp wheel to fully cold, turn on the A/C compressor by pressing the AC button.

Result: Very cold air blows out on the floor and through the dash vents, warmer, but still cool air blows from the windscreen defrost vents. Air velocity is close to the same from all three levels of ventilation, floor, dash, windscreen. There seems to be a little more air volume moving through the vents when the vehicle is in motion, relative to parked, which I would expect.

I suspect that the mechanism that adjusts or blends the amount of outside air passing over the heater core has malfunctioned, leaving the vent to the dash always open and drawing hot air off the heater core. If someone knows of way to test air duct functionality without disassembling the dash, I'd love to know.

Preliminary research on this forum and others suggests the heater valve. I'm going to research further. If others have had a resolved a similar issue, I'm interested to know how.
 

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Set up BMW Standard Tools software on your Windows laptop, run INPA, look at the IHKA eror codes, live data for flap position, fan speed, etc.
Makes it really easy to troubleshoot.
Hit the link below in my sig.

Thank you, sir. That is exactly what I was looking for.
 

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It’s usually one of two things. I just recently fixed this once and for all. First and foremost check your fuses! It’s a 7.5 amp fuse I believe #63. This is direct to the power for the Heater Control Valve. If it’s blown you will get 0V continuous to the valve and will stay open 24/7.

that was my issue.... or so I thought...

replaced fuse and it blew again in little time. Now I started real diagnosis. First measuring voltage at the connector showed 12V constant when set to fully cold . Good. That confirms computer is functioning properly. If not it’s likely a HVAC controller issue. If so move to next step.

I then probed the wires with the valve hooked up and strangely it was cycling open and closed and only reading 0-6V while cycling with controller set to fully cold. I removed the Heater Control Valve and disassembled and thoroughly cleaned all moving parts and contacts. No improvement.

replaced with a new heater control valve and confirmed constant 12V when set to cold and valve closed.

my issue was the valve and I believe high internal resistance was tripping something in the computer And it was fail safe to off condition then trying again. I suppose it does this until the fuse ultimately blows.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Likely the winding in the mono valve (heater control valve) was shorted. I've seen it okay cold, however would short after warming up.
FYI.
 
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