Troubleshooting my HVAC

[Alpinewhite]

Hi All,

I am always getting hot air blown in the leg room and wind shield vents. I tried all positions in the temp knob; incl detents on both sides. Even when I switch of the temp setting by turning completely to the left side I get hot air blown! What could be the problem. I am thinking heater valve or temp setting micro switch. How to check if the heater valve and temp setting micro switch works?

What are the different components that are in the HVAC? How does it work? I saw that this is a good link, http://www.bmwe34.net/e34main/trouble/Heating.htm, but I dont get a complete picture out of it.

Its already 80F in the place I live; help me I am getting cooked.

Mine is a 1995 530I M60 nikasil enhanced car (like onewhippedguy puts it :) )

Thanks
Arun

[shogun]

Is it on both sides the same? Driver and passenger side have separate heater valves.
Heater vales are fully open if they do not get power. So first thing to check if they get power, power is pulsating. Remove the plug from the heater valves and check that. Here is the system explained from an E32, but it will help you.
http://bmwe32.masscom.net/johan/ihka/ihka.html

[Alpinewhite]

Thanks very much for your info and the link. Please update this link in the e34 page of www.e38.org

I will update the results of my troubleshooting as and when I get an answer.

Thanks Again
Arun


Is it on both sides the same? Driver and passenger side have separate heater valves.
Heater vales are fully open if they do not get power. So first thing to check if they get power, power is pulsating. Remove the plug from the heater valves and check that. Here is the system explained from an E32, but it will help you.
http://bmwe32.masscom.net/johan/ihka/ihka.html

[Alpinewhite]

Hi Shogun and others,

I put multimeter on the heater valve connectors when the engine is running. This is what I observed

1. When the temp setting knob is completely on the left (Cold setting detent). 13 to 14 V between the common lead and passenger side lead, 13 to14 V between the common lead and driver side. Is 13 to 14 V reading is good; I thought most electric parts in car works on 12 V

2. When the temp setting knob is completely on the right (Hot setting detent). 0 V between the common lead and passenger side lead, 0 V between the common lead and driver side.

3. When the knob is inbetween cold and hot detent say 78F multimeter shows 13 to 14 V between the common lead and passenger side lead, 13 to 14 V between the common lead and driver side. Should it behave like this in this case?! I thought the reading should fluctuate between 0 and 12 V.

And also I found that the exposed top part of the heater valve is hot to touch, when I have been driving for around 8 miles with temp setting totally off (cold side detent).

I think I have to conclude that the heater valve is gone or stuck somewhere. Is this heater valve serviceable? Heater valve says Bosh on top.

My car is a 1995 530I. I am not sure if I have a IHKA or one of the IHKRs how to tell? Bently says that all 1995 530I has IHKA; I doubt it, I dont have a auto button all I have is the three slides and three circular knobs with AC button and recirc button.

I am a first timer to diy; kindly bear with my questions.

Thanks
Arun

[shogun]

If I understand what you are saying correctly, you cannot turn the heat off regardless of the position of the tumbwheels.

If so, there are several common problems, from most to least common:

1 - Failure of the heater valve assembly

2 - Failure of the solder joints of the two power resistors on the PC Board inside the IHKA Control Module.

3 - Failure of the microswitch inside control head. This is the one on the drivers' side thumb wheel that clicks when you move the wheel to the full cold position.

Some background on how the system works ... by default without any power the heater valves are open. So if you are in Norway in the winter and the system fails, you will have heat and will not freeze to death. How thoughtful.

There are three pins on the heater valves. The middle one shoudl have +12 volts all the time with the key on or engine running. It is not always enough to measure the voltage alone. This signal comes through the microswitch in 3 above. It is possible that a dirty switch could stil show 12 volts with no current flow under load. Better to measure the current draw, should be around 2-3 amps if I recall correctly.

You can also check the continuity of the switch, remove the control panel. There is a small 2 pin connector on the back. There should be close to zero ohms in all but the hottest setting. Full heat is acheived by removing the +12 volts from the heater valves.

The ground signal(s) to close the heater valves comes through the two resistors (40 ohms or so if I remember correctly) in the IHKA control unit. Due to the high current and related heat, the solder joints fail. Many times resoldering these connections will solve the problem. However, I have had some where I've had to replace the control units.

To test the heater valves, you can try (at your own risk all usual disclaimers apply) removing the connector and jumping +12v to the middle pin, and grounding the other two pins with a jumper. (might want to check the resistance first, if either of the solenoids is shorted this is not a good idea. Resistance should be +/- 13 ohms or so).

If the heater valves are working ok, then doing this should shut the heat off.

LMK if you have any questions about how to troubleshoot the system. I still don't fully understand it and its operation, but probably understand it better than most.

Jeff - Sponsoring member IATN (www.iatn.net)

How to open the heater valves
http://www.bimmerboard.com/forums/posts/111837/

And check the IHKA module at these places where the red arrows point. You might have to resolder there
http://www.voss-tronic.de/bmw/IHKA.jpg

[Alpinewhite]

Hi Shogun and others,

I did the heater valve test by jumping +12v to the middle and grounding the other two. I hear a click when I close the circuit and I can get cool air inside. Good news is I did not buy a new heater valve and put it on (thanks to Shogun). Bad news is it is not the heater valve, it should be the control module :(.

Problem specifically looks like that there is no proper current flowing through the heater valve for the solenoids to get activated and close the valves. I confirmed that the potential diff (voltage) is good 12V with a multimeter.

I will remove the control module this weekend and let me have a look at it. With out a schematic I can't do much. Does anyone know how the heck this control module work?

Mine is a IHKR III. Now I am glad it is not a more complex IHKA.

Any tips / help will be highly appreciated.

Thanks
Arun

[Alpinewhite]

I can rule out the temp setting knobs right? Since I am getting 12V in the leads and just not enough current it should be control module right?

Thanks
Arun