HVAC Nightmare: Heater Control Valve

[Frankie]

Searching the archives (keywords: "heater control valve"), I see those afflicted by a hot-air-all-the-time HVAC problem. Well, now I have it too .

In my case, it's hot air at the left (driver side) defrost/footwell. All other controls function normally.

Archived posts say: replace heater control valve. Fault code readout confirms: left side heater valve. So I replaced the HCV with a new one. No change. Other posts say disconnect batteries to reset IHKA controller. Did that. No change. Fault code remains: left side heater valve.

What the....?

So I tested the new HCV. Using 12 volts, the solenoids ground just fine. In fact, my old HCV does too!

I'm beginning to suspect this is an electrical problem with the A11 control module, NOT a hardware problem. The ETM shows A11 pin 21 controls the left solenoid. Apparently, it's simply not receiving a ground signal from that pin.

Archived posts indicate some of you had this exact same problem but no one reveals how it was ever resolved. This is my worst nightmare: an HVAC problem buried in uncomprehensible and outrageously expensive circuitry.

[Timm]

The heater matrix (both sides) is always hot - even when no heat is demanded, it is the mixing flaps that control the heat into the cabin. The mixer flaps are moved by stepper motors under control of the IHKA unit. Disconnecting the battery re-initialises the flap positions so that was worth a try.

The question is whether the mounting points for the stepper motor is damaged or the IHKA is not demanding the motor to move. The most common fault is that the mounting gets damaged.

[Imndeep]

Frankie, I have the same issue as you. The next step I was going to try is to replace the IHKA controller itself 64 11 1 392 082, if that doesn't work then the sword 64 11 8 390 015 then try the limit switch, 64 11 8 367 838, all of which are not cheap to replace!.

Good Luck,

Chris

[cartoonz]

both of you need to read Timm's post again....

[91e34M5]

Good luck....I have a 91 M5 and a 91 850 both with the same issue. On the M5 I clamp off the heater hose to the interior in the Summer. On the 850, it slowly and eventually transitions from heat to AC or from AC to heat.

[Bryson]

The IHKA controller in the console was the culprit in mine. I broke down the circuitry and found where there was a supply voltage issue so that it wouldn't ground and close the heater valves. I supplied voltage to the pin and all has been 100% for the past four years or so.

Sorry, since it was so long ago and I didn't document it, I can't recall exactly what the fix was. But it is possible! I had never seen it mentioned before on the boards at that time either, but I knew that there was an issue with the e32s so I plugged on anyway.

Good luck, I would replace the IHKA controller or start digging into wiring diagrams

[Wuffer]

Likewise, mine was also the console unit - replaced and all is well.
Bryson, wanna fix my old one? 8-)

[Frankie]

The heater matrix (both sides) is always hot - even when no heat is demanded, it is the mixing flaps that control the heat into the cabin....

This makes sense....it's how a water faucet works.

But then, what's the purpose of the heater control valves? That is, if water flows all the time and the blend flap controls the output air temp, why the need for a valve?

Presuming the valves are for some other purpose than to regulate vent temp, why do I have a fault code that reads: left side heater valve?

So...please confirm my understanding:

1) Heater control valves are either fully open or fully closed (no intermediate positions) and therefore do not regulate vent temperature, right?

2) The aux water pump, then, must come on when HCVs are open and turn off when closed, right?

[NickF]

From the IHKA manual:

"Temperature regulation on E31 vehicles is accomplished by solenoid actuated water valves,
normally help open by spring pressure, are pulsed closed by the IHKA E31 control module
to regulate the flow of how coolant through the heater cores (and, thereby, the core
temperatures)."

The manual is on e31faq on Wuffer's site BTW.

I had the same problem, it was the heater controls on mine too. I still have a problem in that the temp changes are much too sudden and the fan control is mad, so I think that's the sword. If you have access to DIS then you can get diagnostics from the IHKA module. It tells you what each sensor is reading (including core temps, ambient, etc) and what position each control is set at (at least what the module thinks they are), plus it gives you fault codes. I did a lot of digging on this problem and it seems that the IHKA control module itself is rarely at fault, it's normally the heater controls.

[Bryson]

The sword repair is also a DIY if you feel like getting involved in some fairly simple circuitry. I just did mine a few weeks ago and it works great Search for the e32 DIYs and you'll save yourself a pretty penny!

Tom, I'll be sure to crack my HVAC panel open next time I have the console out for you

The heater valves do more than just open/close. The aux pump is only needed at low rpms as there isn't enough pressure to drive flow through the heater core. My understanding is that it is not tied to the opening/closing of the heater valves, can't be sure where this impression came from though

[rchan11]

How much is the IHKA?

[Timm]

This makes sense....it's how a water faucet works.

But then, what's the purpose of the heater control valves? That is, if water flows all the time and the blend flap controls the output air temp, why the need for a valve?

Presuming the valves are for some other purpose than to regulate vent temp, why do I have a fault code that reads: left side heater valve?

So...please confirm my understanding:

1) Heater control valves are either fully open or fully closed (no intermediate positions) and therefore do not regulate vent temperature, right?

2) The aux water pump, then, must come on when HCVs are open and turn off when closed, right?

The heater control valves maintain the correct core temperature in each side of the matrix. The temperatures are monitored by two thermocouples, one for each side of the matrix. Once the matrix is up to temperature you will hear the valves clicking away maintaining the correct temperature.

This set temperature is needed by the IHKA to approximate the correct settings for the mixer flaps (as it takes a while for the heat to be measured by the 'sniffer' in the control panel).

If the water valves were left open all the time, the matrix temperatures would constantly change and the correct flap settings could not be approximated. You would also end up with very hot air coming out of the vents when pushing the engine hard - just at the time you least need it!

The water valves and thermocouples essentially provide a 'thermostat' for the matrix. The mixer flaps can then be finely controlled to provide the correct cabin temperature - without this 'thermostat' the cabin temperatures would fluctuate quite considerably.

[TxGR8White]

Frankie, I have the same issue as you. The next step I was going to try is to replace the IHKA controller itself 64 11 1 392 082, if that doesn't work then the sword 64 11 8 390 015 then try the limit switch, 64 11 8 367 838, all of which are not cheap to replace!.

Good Luck,

Chris

the "sword" controls the fan speed.
I agree, most likely the stepper motors are not securely mounted anymore. You can remove the MID and look back there to see if the flapper linkages are actually moving as you switch the HVAC control between the different settings.

[taylorpatterson]

The IHKA controller in the console was the culprit in mine. I broke down the circuitry and found where there was a supply voltage issue so that it wouldn't ground and close the heater valves. I supplied voltage to the pin and all has been 100% for the past four years or so.

Bryson, I too have this issue of heat always on. I defeat it by pressing the recirculation button which seems to also turn on the A/C to some extend. But then it gets too cold eventually so I would really like to learn more about how you fixed this by "supplying voltage to the pin."

Can you elaborate? Was this a pin INSIDE the IHKA or something leading TO the IHKA? Were you able to determine why the voltage was not being supplied, as in, was this a broken lead or do you believe there might have been something else wrong but you found this to be a viable workaround?

Where is the IHKA located - meaning are there 'brains' in the form of some other module behind the main Control Module located below the OBC?

Sorry for all the questions - just trying to understand things before I start tearing apart the car. Thanks in advance.

[TxGR8White]

IHKA controller is located on the firewall (in the cabin), accessible from the passenger footwell

[taylorpatterson]

Is it one of the three black boxes located in the 'rack' with the LKM?

[Timm]

You can remove the MID and look back there to see if the flapper linkages are actually moving as you switch the HVAC control between the different settings.

Now, that's a good idea!

[Frankie]

...The [IHKA] manual is on e31faq on Wuffer's site...

Thanks Nick! I forgot about this resource. (Good to hear from you. If you remember, you gave me moral support about a year ago with a front-end vibration problem.)

How much is the IHKA?

Over $1000. This is what I meant when I said "outrageously expensive circuitry".

The heater control valves maintain the correct core temperature in each side of the matrix..

Informative again, thanks Timm! Your new info has changed my take on the problem.

The concensus seems to point toward the left temperature control wheel as the culprit, not the IHKA module. Perhaps this is the chain of events:

1) Left temp control wheel malfunctions. "Shows" full hot to the IHKA module.

2) IHKA commands left HCV to full open and mix flap to full hot blend.

3) IHKA throws "left side water valve" fault, since valve is open even when engine is cold.

I will perform some wiring tests next week on the HCV and look at the left mixing flap motor. I will also see if more diagnostic readouts of the IHKA are possible.

Thanks to everyone who chimed in. This help makes these forums such a great resource.

[Timm]

The driver's control wheel will over-ride the passenger's setting when at the extremes of travel (past the detent). If you feel the passenger's control wheel is the problem, adjust the driver's control to fully cold, the passenger temperature should now drop.

[TxGR8White]

Is it one of the three black boxes located in the 'rack' with the LKM?

nope, it is in the passenger footwell

[Bryson]

Bryson, I too have this issue of heat always on. I defeat it by pressing the recirculation button which seems to also turn on the A/C to some extend. But then it gets too cold eventually so I would really like to learn more about how you fixed this by "supplying voltage to the pin."

Can you elaborate? Was this a pin INSIDE the IHKA or something leading TO the IHKA? Were you able to determine why the voltage was not being supplied, as in, was this a broken lead or do you believe there might have been something else wrong but you found this to be a viable workaround?

Where is the IHKA located - meaning are there 'brains' in the form of some other module behind the main Control Module located below the OBC?

Sorry for all the questions - just trying to understand things before I start tearing apart the car. Thanks in advance.

Taylor, I'm referring to the controller beneath the head unit - the one in the console.
The pin was indeed inside the IHKA controller (the one I'm referring to in the console) and my fix was a viable workaround for some internal failed circuitry that reflowing the solder joints did not fix. As the pin is supposed to get voltage at all times, bridging it with another has solved my problem.

I seem to remember that there was something to do with the AC and/or recirc that would force the system cold again, but it was so long ago that I've forgotten now.

I'll be pulling the console out to remove all the automatic wiring harnesses, so I'll be sure to open it up, get some details, and snap some pictures then. I'll probably just update this thread, so make sure you've subscribed to notifications

[taylorpatterson]

I'll be pulling the console out to remove all the automatic wiring harnesses, so I'll be sure to open it up, get some details, and snap some pictures then. I'll probably just update this thread, so make sure you've subscribed to notifications

You doing it this weekend? Want some company/help?

[Bryson]

I wasn't planning on doing it this weekend, I suppose I could tomorrow, but are you still up north near SLO or are you going to be in SD? I'm leaving on Sunday afternoon for a week in San Diego

[Frankie]

...The IHKA controller in the console was the culprit in mine....

...Likewise, mine was also the console unit...

Uh....after re-reading this, I think we have a terminology problem. Are you guys referring to the control panel (head unit, with temp control wheels and push buttons) or the control module (behind the dash, in front of heater box)?

[Wuffer]

I am referring to the unit on/in the center console, with the roller wheels and fan controls.
Located below the radio, above the shifter - the one with crummy roller wheel lighting... 8-)