Heater problem

[amw662158]

Hi, I have a 1999 540 wagon with a weird heating issue. The heater blows heat (in fact, alittle too much heat) for about 10-15 minutes then switches to cold air. Even though I live in the Bay Area and a cold morning is 46 degrees, that is still cold in the car. Temp gauge is in the middle always. The center vent is set to block fesh air, i.e. three red dots.

Any help will be appreciated.

[TheAngryBear]

What temperature do you have the IHKA set to? Do you have it in auto mode?
I have noticed that even with it being out of auto mode it does what it can to achieve the temperature setting. Say you have the fan on low, it does high heat output. Fan on high, low heat output.


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[amw662158]

75 on both sides and on auto.

What temperature do you have the IHKA set to? Do you have it in auto mode?
I have noticed that even with it being out of auto mode it does what it can to achieve the temperature setting. Say you have the fan on low, it does high heat output. Fan on high, low heat output.


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[TheAngryBear]

That seems normal. 10 mind to heat up the cabin to 75 then it maintains that temp and doesn’t have to push out super hot air. Also keep in mind that the system (during steady state) tends to push hot air out the floor vents and cooler air out the top. This does two things: 1) hot air rises and 2) humans tend to feel refreshed with cool air on the face, warmth tends to make us drowsy.


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[geargrinder]

Amway - there's a number of things that might be wrong.

Would be ideal to scan the car for codes in the Climate Control head aka "IHKA". It might tell you just what is wrong. If not it could be the 'sampling fan'. That little port in the CC unit has a fan behind it that sucks in air to determine the interior temp. That can get clogged with lint and garbage and go wrong and it tends to look like what you see, because the inside of the console starts to warm up before the cabin, but because its not sucking a good air temp sample in, it doesn't know that. That might not throw a code... if its a flap actuator or something else then it indeed would likely throw a code. If you have INPA you can look at live readings and could tell for isntance what temp the module is reading... if it says "75F" but the car is 46F inside, you know there's something there.

There's some threads on this, some in the E38 or M5 or X5 world, same modules so it all applies.

[TheAngryBear]

There certainly could be something wrong with the system but the description of “heat for 10-15 minutes then cold air” is in-line with standard operation that I don’t think that is the issue. Likely the “cold air” is in contrast to the hot air that had been blowing. Similar to immersing your hand in hot water for a bit then room temperature water feels “cold”.
Maybe I am off base on the cold air on top theory but that is how my system works with no scanned errors...
More on the IHKA here http://www.e90post.com/forums/attach...1&d=1327080092 which discusses the valves being pulsed to control temperature of IHKA airflow to meet the settings on the IHKA (pg 11).


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[amw662158]

I think I will start with Geargrinder's suggestion for clening the IHKA unit. I have 2 other e39's and neither of them do this, btw.

[TheAngryBear]

Fair enough, just providing my perspective and experience.
How do the other two behave in comparison?


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[OldCarGuy]

Did you ever resolve this? My car has started doing the same thing- too hot for 10-15 minutes, and then too cool, to sometimes no heat whatsoever. No INPA so I can't read codes.

[Qsilver7]

Did you ever resolve this? My car has started doing the same thing- too hot for 10-15 minutes, and then too cool, to sometimes no heat whatsoever. No INPA so I can't read codes.

If the IHKA is set to AUTO (air distribution) as well as AUTO (fan speed control)...make sure that the dash's center vent is NOT blowing air downward.

You wrote that you have the stratified air dial set to the neutral...so make sure that the louvers in the dash's center vent is blowing outward/upward....and NOT downward. There is a phenomena that can occur when air is blown downward or sucked into the little vent on the lower left side of the IHKA control panel. There is a small thermistor inside the left grid that helps the IHKA regulate the cabin's temperature based on what is set on the display.

See the data below for more details about what was mentioned above. If air from the center vent is being drawn into the IHKA and it is hotter or cooler...then it can affect the IHKA in determining how to maintain the selected temp:

[geargrinder]

You wrote that you have the stratified air dial set to the neutral...

Actually OP has his set to full hot. I kinda breezed over this before:

The center vent is set to block fesh air, i.e. three red dots.

OP - the center vent control isn't a traditional 'fresh air vent' really. Its a "manual override blend" switch. It is basically to give you cool or warm air up on top to fine-tune comfort while letting the main HVAC head actually stabilize the whole cabin temp to the requested setting. It's not just a 'fresh air' switch, but AC-air vs heater-core air. One of my favorite in-cabin BMW features actually. Middle between red/blue means "don't override the HVAC for warmer or colder". Setting to all reds means "send heat ALL THE TIME out the center vents, regardless of what is required at the lower vents to manage total cabin temp".

Noting that you're on 3 reds would:
1. Definitely explain why you get too much heat at first
2. Not explain why it goes too cold which still says something is wrong

Imastick w/ my recc to scan the head for codes. That thing isn't dumb, it might very well have noticed what the problem is.

[amw662158]

So, I took out the climate control unit to remove the lint that gets into the vent, but someone had already done that. Then, i tried the control unit from my 2000 540i, but, even though the RealOEM parts numbers were the same, the stickers on the two units showed several different numbers. The unit from the 2000 didn't work at all in th 99. Tried driving without a control unit installed while I suffered from the paralysis of analysis, but the the footwells became uncomfortably warm here in the Bay Area. I finally bought a used unit with identical sticker numbers on it and now have constant, controllable heat -- the unit works as it should.

Thanks to everyone for their comments. A scan of the unit showed four codes which I don't remember, unfortunately.