Heater Control Valve Troubleshooting

[Frankie]

For those who would like a practical summary of the lessons learned in my HVAC Nightmare thread, I offer my latest write-up:

Heater Control Valve Troubleshooting

Feedback welcome.

[8eights]

Awesome stuff, Thanks again Frankie for yet another awesome remedy!

[EEDegreeToDrive]

For those who would like a practical summary of the lessons learned in my HVAC Nightmare thread, I offer my latest write-up:

Heater Control Valve Troubleshooting

Feedback welcome.

Frankie-- Nice writeup, I commend your effort. Here's some feedback

Troubleshooting procedures should start with the most common failures, and then work down to the more obscure procedures. You should also supply instructions and you left out the most obvious cause.. A= Action, D=Decision

D1) Is Fuse 1 (or is it F3? It's not clear on the diagram) blown? Yes, replace fuse, No, continue (Note: this procedure may be used for other BMWs with dual climate control, so F1 is used in the 8 series)
A1) Measure the from Pin1 to shassis ground
D2) Is there 12V at the HCV connector? Yes, go to A2; No, Probably a broken wire, bad connection, or a fault in the PCB microswitch of the IHKA

A2) Measure resistance of HCV pin 1 to Pin 2; then Pin 1 to Pin 3. You should measure xxx ohms (probably ~10-50 ohms if I had to guess)

D3) Is either valve open circuit? Yes; Rebuild/Replace HCV No; Proceed to A3

A3) Apply 12V to HCV Pin1, Ground the two other pins repeatedly. Listen for noise
D3) Can you hear the solenoids ticking? Yes: Go to A4 Temp test; No: Solenoid is not moving, Rebuild/Repace HCV

A4) Temperature Test: Apply 12V on HVC Pin1, and Ground the two other pins securely. Start car and check if car blows heat.

D5) It it getting hot in the car? Yes: Your HCV is not closing properly; Replace/Rebuild HVC No: Your HCV is working properly, there must be a control problem or broken wire. Proceed to A5

A5) Remove 12V and ground connections from HCV. Reconnect HCV connector.

A6) IHKA Wiring Test: Remove connector at IHKA. Ground Pins 21 & 23 on IHKA connector (not on the IHKA). Start car and verify temperature again:

(This next one is just an idea...)
D6) It it getting hot in the car? Yes: Your wiring is damaged and your HCV's path to ground is broken. Troubleshoot broken wire. No: Your HCV is working properly, there must be a control problem on the IHKA

Potentially add additional options for troubleshooting the IHKA, including bad transistors, broken traces, misbehaving MC, etc
<end>

I also don't know what you were trying to say with "Continuity at pins 2 and 3". I'm not sure what you're asking, is there continuity between the two pins? On the connector, or on the HCV? If measuring back to the IHKA via 2&3, you won't be able to easily measure that because the transistors act like opposing diodes. I'd measure each half of the solenoid, (as suggested above) and then measure the voltage at pin 2 & 3 using a 1K pull up resistor to 12V.


Anyway, wife is beconing me, will contribute more later!

[rchan11]

Thanks for the write-up Frankie!

[Timm]

Thanks Frankie, another great addition to your site.

[Frankie]

Thanks for everyone's feedback!

Troubleshooting procedures should start with the most common failures, and then work down to the more obscure procedures....

Thanks EE. I appreciate the help you've given me in the past!

My objective is to keep the DIY as simple as possible, and therefore some assumptions are noted in my write-up: 1) you won't be reading my DIY if you weren't having a hot-all-the-time problem and 2), no wiring faults are present.

The later is a mostly safe assumption, I think, because I have not really seen this within our group. Nonetheless, my write-up states wiring continuity should be checked for those who want to be absolutely sure.

Potentially add additional options for troubleshooting the IHKA, including bad transistors, broken traces, misbehaving MC, etc

As mentioned, I have intentionally NOT included this stuff as it is simply beyond most of us (I wouldn't know how, anyway!). I'm targeting the amateur DIY'er. In most cases, parts replacement is the only practical alternative.

I also don't know what you were trying to say with "Continuity at pins 2 and 3"....

You're right. I have changed the wording for that test and added a brief explanation of exactly how to perform each of the 3 tests - at least, how I performed the tests .

[AJe31]

Thanks for the write up gentlemen- I replaced heater control valve on AJs car...I have 12v output at the power pin, but open circuit at the other two inputs indicating the control board is bad.
I have seen them for sale with a pink/purple connector instead of the yellow connector.

Any idea if this board is the same? P/N 64118367838 appears correct.

[Timm]

The 12V supply comes from Fuse 1 (Hot at all times) and if the drivers temperature control is set to anything but maximum it will reach the heater valves. The two other connections to the water valves are transistor controlled by the IHKA - and they will appear as open-circuit if measured by a multimeter.

The two transistors pull the other side of the valves low (to 0V) to CLOSE the valves.

So, if you are not getting HOT water it is very unlikely to be the IHKA and more likely coolant is not reaching the heater matrix. More info here:

https://www.meeknet.co.uk/e31/E31_He...eplacement.htm

[AJe31]

Thanks Timm
Dash Vent and driver door vent are hot all the time...I tested at harness with coils unplugged...appears I need to retest with Heater valve coils connected to circuit.
I was getting 0V, 0ohm and intermittent ground one side and open on the other regardless of temp setting. I suspect a mixing flapper may be broken as well...but was a place to start.

[Timm]

If you have heat when you don't want it, set the drivers temperature wheel to the coldest setting (past the detent 16C) - probe the three connections with everything still connected in respect to chassis (have the negative probe on the chassis jump ground-point on the suspension strut housing). Using a really sharp probe pop through the three wires - you should have 12V, 0V and 0V.

[AJe31]

Heater on
Pass coil 14V, 156F water in 150F water out HCV (optical pyrometer)
Driver coil 14V, 168F water in 138F water out HCV

AC on (max detent)
Pass 14V 166F water in 148F water out HCV
Driver 14V 171F water in 162F water out HCV

Same results- resistance test 0 ohm reflects open circuit- then no change when voltage applied, maybe bad power supply or ground etc as common to both circuits... IHKA control board not dropping HCV pin to 0 is culprit and requires replacement?

From photos the purple connector on available boards appears to be same shape as yellow connector...seems odd

thanks...AJs Dad

[Timm]

I'm not sure if 'AC on (max detent)' is 16C or 32C - if it was 16C then quite likely the IHKA output stage has failed - if it was 32C then test at 16C

[EEDegreeToDrive]

I'm not sure if 'AC on (max detent)' is 16C or 32C - if it was 16C then quite likely the IHKA output stage has failed - if it was 32C then test at 16C

A few things...
Reminder, As many of you know, the HCV is fail open. Disconnecting the plug, or failure of the +12V or the transistor switched ground(s), leads to full heat. Additionally, the valves seals actually can fail, and this will 'leak' coolant through the HCV.
A second thing that happens is the blender doors get stuck and/or servo motor actuators come loose, and certain vents can end up with no heat or full heat.

There is a Common Problem where the microswitch for the MAX HEAT indent fails.
Normally, when set to max heat, the microswitch cuts the +12V supply to force the HCV to heat.
The opposite of that is: when NOT set to max heat, the +12V flows through the microswitch to allow the HCV to switch.

Often times, if you disconnect the HCV and measure it, you'll see +12V, but if you stick an actual load on there (like a test light, or a parking light bulb w/ wires), you'll find that the +12V is pretty high impedence.

EDIT: This is caused by a bad MAX heat microswitch, it doesn't conduct enough after years of a ~1-2A load.

The easy solution (what I did with my car) is to simply drag a solder ball across the microswitch terminals in the IHKA control board (the knobs/dials), effectively disabling the MAX HEAT function and guaranteeing that the HCV has the 12V it needs on the 'common +' terminal.

[AJe31]

ah thanks Scott...that may explain why both circuits are calling for full heat..worth a try first prior to the IHKA control board replace...
HCV is new...old one had electrical functionality
Would not be surprised if there are some issues with blender doors as well..

[AJe31]

Removed control board today-
Pins 11-12 open on full heat (on bench- no continuity)
closed (continuity) on bench in every other setting

Soldered pins together ran car- 14V both solenoids in all positions
Unsoldered jumper from board

Began removal of "rear" board that contains micro switch..appeared that may cause damage so stopped & sprayed micro switch plunger with de-oxit from front.

Appears I am back to buying a new control module (computer board)..unless anyone has a recommendation!

[AJe31]

Purchased used 1995 850ci computer control module board 64118367838 on ebay $360 (+ tax )- spent today upside down installing it.

Results car running (volts to ground at strut mount):

Heater on
Pass coil 0V, 184F water in 165F water out HCV (optical pyrometer)
Driver coil 0V, 184F water in 165F water out HCV

AC on (max detent)
Pass .9V 156F water in 126F water out HCV (hose cool- likely no flow)
Driver .9V 156F water in 126F water out HCV

I'm an ME so the water temps were helpful ...I anticipated full voltage (14V) in one of the settings (likely heat) similar to what I had with bad board, that didn't happen.

The driver side center vent blew hot before and is now cold (AC on), driver door vent was hot and is now cold..heat and AC appear to function ok..so perhaps internal flaps are ok as well.

Scott do you want old board for research/repair? Two output pins in yellow connector slightly bent...assume they were "connected"..otherwise would be pushed over.
Anyway everything appears to work! thanks for help..

Ajs Dad