HVAC Nightmare: Heater Control Valve

[pollack137]

Hi Frankie, That corrosion on the connector would be the first thing to fix. I wouldn't be suprised to see your problem fixed once you clean it up.
"I cleaned this off as best I could and will re-assemble in the morning."- YES! try this before tackling any re-soldering. Also, EEdegree To Drive said "In the old Mercedes and Ford's I've owned, there's also a temperature sensor... For the BMW's, there's likely 2 or more." this is true, there are two of them in the main heater box that will need to be tested, they may be able to be swapped from side to side to check them but look after the corrosion problem first.

[Frankie]

I'm ready to declare this effort a total loss and a most disheartening outcome .

With everything back together, there is still no signal at pin 21, x610 (left HCV).

I have to conclude the problem lies buried in the control module - like I suspected all along. This is beyond repair for people like me. I looked at all the solder joints and traces. Nothing looked unusual to my untrained eye. Actual testing of the board will require skills from beyond.

...there's also a temperature sensor

Doubtful: this would throw a fault code. The only fault indicated is "left side heater valve".

Like I said in my opening post, this is a nightmare problem whereby the issue likely lies obscured in incomprehensible circuitry. It's problems like these that will eventually force many modern cars to an early grave as they become unserviceable.

For now, I will use my heater-hose-disconnect as a workaround until the cold season returns. In the meantime, I will keep an eye out for salvaged control modules and perhaps look into the "voltage follower" idea suggested by Bryson....

...and add this to my list of unrepairable E31 problems.

Oh, and a grateful "thanks" to all those who offered assistance!

[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.

Dont feel bad about it... i gave it up too...join the club!

[91e34M5]

UPDATE- I was troubleshooting my full time heat to the passenger side this week and found my problem. Both of the solenoids in the HCV were clicking like they were supposed to, but regardless of how I had my passenger temp wheel set, it was blowing full hot on that side. Driver's side seemed to be working properly. I was assuming it was a sensor or circuit board issue. I decided to just remove the HCV and block it off for the summer. Being the industrious person I am, I disassembled the HCV to take a look on the inside. I found that the plunger tip that seals on the seat was broken which left the valve on that side in the full open position. The heater core is currently disconnected but I will follow up when I install a new HCV.
Cold AC...here I come!

[pollack137]

I found the same thing had happened on my driver's side valve except mine didn't click.

[taylorpatterson]

UPDATE- I was troubleshooting my full time heat to the passenger side this week and found my problem. Both of the solenoids in the HCV were clicking like they were supposed to, but regardless of how I had my passenger temp wheel set, it was blowing full hot on that side. Driver's side seemed to be working properly. I was assuming it was a sensor or circuit board issue. I decided to just remove the HCV and block it off for the summer. Being the industrious person I am, I disassembled the HCV to take a look on the inside. I found that the plunger tip that seals on the seat was broken which left the valve on that side in the full open position. The heater core is currently disconnected but I will follow up when I install a new HCV.
Cold AC...here I come!

Is the HCV the "Heater Core Valve"? Where is that located?

[pollack137]

I'm refering to the heater control valves (beside the aux water pump), I assumed 91e34M5 was as well.

[Dr. T]

My HVAC update:

After mounting and remounting and re-bonding and re-epoxying my passenger-side stepper motor a dozen times, I figured something must be wrong with it and ordered a new one from Gault to give it a go...

Well, now 2 weeks later...all it well with temperature selection and there's no more 'stuck flap' sounds coming from the center dash. Guess there was an internal problem whereby it wouldn't respond to the "ends of travel" resulting in overtorqueing and breaking itself right off the mount.

[91e34M5]

Is the HCV the "Heater Core Valve"? Where is that located?

Yes. The Heater Control Valve under the hood, driver side near the firewall adjacent to the auxiliary pump. If you want to block off the piping after removal, 1/2" threaded galvanized plugs using the existing clamps work perfectly for a summertime fix or while you order parts.

[Frankie]

I think my car is mad at me for plugging the aux pump heater hose:

For weeks now I would - occassionally - see a puddle of coolant on the ground under the HCV area. This made no sense. How could water be leaking downstream from a plugged system? I reasoned system back pressure must be pushing water out, past the plug. I removed my steel plug and noticed that I had also neglected to consider something important: steel rusts.

After cleaning the plug and painting it with high-temp spray paint, I re-installed it. This time, I used two hose clamps to better contain system pressure.

It still leaked. What the...?

In disgust, I completely removed the HCV to get a better look. I then saw the problem. When I removed the HCV passenger-side supply hose, hot water came out. Wow! There was water, under pressure, still present in the HCV circuit. And with the HCV's wide open, water was leaking out the aux pump, easily getting past the tin foil wrap I had put over the end of it.

Apparently, water pressure makes its way up the heater core return line, out the heater core and into the L/R supply hose from the HCV and then, out the aux pump. So....for anyone wishing to plug-off their HCV system, be aware that you'll need three - count 'em three - plugs: one for the main aux pump supply hose, and one each for the L/R output hoses from the HCV itself! And paint those steel plugs! Who'da thunk?

P.S. I have decided to try getting my circuit board repaired locally before attempting other options, but won't worry about this until the 104 degree heat passes, probably sometime in...October?

[Imndeep]

I replaced the HCV valve and still have the hellfire hot air.

[EEDegreeToDrive]

Well folks-- I'll be drudging this topic back into the foreground..

My climate control has some similar effects.. Main symptoms:
1) Turn everything off and it gets really hot in the car, even with the sunroof/windows open (forced hot air through the vents)
2) Turn on climate control with reasonable temperatures set (70, each side), A/C turned on, and the car stays nice and comfortable
3) Turn on climate control low temperatures set (driver's side to the MAX cold position) , A/C turned OFF and it gets nuclear hot in the car. Main vents blow outside-air temp, windscreen/door defrost vents are so hot it almost burns to leave your arm on the door.

I'm suspecting I've got a bad heat control valve, which is always allowing heat circulation and that with my A/C on, the cool air happens to overpower the hot air.. Regardless, as 'ol Arnie Sperminator would say.. "I'll be back" to share my findings.

I've also noticed a slight, periodic change in engine pitch at around 3000 RPM, I believe caused when the compressor kicks on/off.. It sounds and feels good when it's running, but then it seems to purr extremely smooth.. On 30 seconds, Off 30 seconds, etc.

[thelongeride]

I had the hot foot from hell symptom. I replace the heater control valve...problem fixed.

[Frankie]

Hi EE! I appreciate your helping me back in April. Now, maybe I can help you:

...I'm suspecting I've got a bad heat control valve, which is always allowing heat circulation and that with my A/C on, the cool air happens to overpower the hot air...

First, get your HVAC fault codes read. (Alternatively, you could do some electrical testing out at the HCV. But if your tests return OK, you'll need to know what your mother board "thinks".)

Second, when your a/c is off, the defrost (upper) vents open, even though uncommanded. (The Germans seem to think you always need air coming out up there.) Only when your a/c is on do those vents close, concentrating cool air thru the dash vents. So, your a/c is not simply "overpowering" the heater. If you have an HCV failure, you'll always get hot air out the defroster with a/c off.

Third, with HVAC off and windows or sunroof open, the air compensating flaps (which adjust ram air effect) do not work, and allow air into the cabin based on road speed - the faster you go, the more air thru the vents.

This should explain #1-3 of your situation.

So now....is the hot defrost air coming from the driver or passenger side or both? The answer may help you locate the offending valve. Use this info in conjunction with your fault code results.

[EEDegreeToDrive]

I had the hot foot from hell symptom. I replace the heater control valve...problem fixed.

Yup-- I like that description "hot foot from hell symptom", I've got that.
Interestingly, With the A/C switch off, I can feel the hot air coming from the defrost vents (windscreen & both doors)
I don't recall if my feet are hot all the time, or only when the A/C switch is off, but I kind of recall they are hot all the time.

Hi EE! I appreciate your helping me back in April. Now, maybe I can help you:

First, get your HVAC fault codes read. (Alternatively, you could do some electrical testing out at the HCV. But if your tests return OK, you'll need to know what your mother board "thinks".)

Second, when your a/c is off, the defrost (upper) vents open, even though uncommanded. (The Germans seem to think you always need air coming out up there.) Only when your a/c is on do those vents close, concentrating cool air thru the dash vents. So, your a/c is not simply "overpowering" the heater. If you have an HCV failure, you'll always get hot air out the defroster with a/c off.

Thanks for this insight-- The car is nice and comfortable with the A/C switched on making me believe the flaps are working OK AND the control unit is doing what it is suppose to.

It seems like my issue is that one or more of my solenoids are not closing. So I'm thinking one of the following possibilities:
a) The solenoids are damaged (my cooling system was in pretty bad condition, non-BMW fluid, so this wouldn't surprise me at all)
b) The solenoid driver transistor/circuit in the control unit is bad
c) The wiring to the solenoids is bad
d) The 7.5A fuse is blown

Third, with HVAC off and windows or sunroof open, the air compensating flaps (which adjust ram air effect) do not work, and allow air into the cabin based on road speed - the faster you go, the more air thru the vents.

This should explain #1-3 of your situation.

I'm glad to know how that works. I like cruising down the road with sunroof popped and not having to run my HVAC system and days-numbered sword. I wish there was a position for fan OFF where the HVAC would stay on. In my E32 I had a damaged sword so I cut the transistors out of circuit leaving only the bypass relay. I then had three positions: OFF, Forced Ventilation, FULL BLAST. If I have to pull the control head unit, perhaps I'll bias the fan-speed potentiometer so that low is actually 'stopped' ...

So now....is the hot defrost air coming from the driver or passenger side or both? The answer may help you locate the offending valve. Use this info in conjunction with your fault code results.

I have only witnessed the heat coming from the defrost vents on both sides, which I suppose is the driver's side valve. Based on mine and Nevile's non-directional hot feet, I suspect the immense, unregulated heat is radiating from the heater core to the foot well area.

This *could* also explain the nuclear hot CD player and MID (which subsequently fades to amber when hot)

Thanks for the tips everyone! I'll try to take some pictures to post with my electrical troubleshooting ;-)

My plan is to:
1) Check the 7.5A fuse that drive the solenoids
--If this is the case, then stop, enjoy a beer.
2) Disconnect the connectors to the HCV's and provide 12V (after checking with the ETM first) to each solenoid.
--If I'm right and the solenoids are in-fact bad, I'll still have a bunch of heat inside the car. Stop, have beer, order new valve from Charlie. If the 12V actuated solenoids stop the heat, then I've got a control issue...
3) Connect meter/scope to solenoid outputs and verify control unit is varying solenoid signals
3a) turn to full blast heat, signal should be nill
3b) turn to setpoint less than current temperature, signal should be modulating, or even constant
--If output signals aren't varying as predicted, its time to [have several beers and put off] tear into the control unit...

I'll try to get to it this week, but the wife wants me to refinish a table first.

[ByMW]

Yes, it really does take an electronic engineering degree to drive one of these cars...
What does it take to refinish a table?
(Enjoying all the educational gems in this thread.)

[EEDegreeToDrive]

I went ahead and replaced the HCV, it was ~$150 on E-Bay for a genuine Bosch part.

1) Disconnected battery ground, Moved +Batt jump start block out of the way, Moved engine harness connector out of the way
2) Removed Cabin-Air Filter assembly (5 bolts + plastic nubbin) (Some imbecile had removed/reinstalled the cabin air filters backwards! Dirty side toward passengers!)
3) Disconnected electrical connector for Aux Water Pump and HCV
4) Started to remove HCV/Aux water pump assembly...

...Then...


<SNAP>

Aux water pump stem broke off... I should have listened to the advice and ordered the aux pump too! I have to place an order to Gault anyway to order a pair of heater core hoses I forgot, so I'll just add the pump to my list.

'Tis OK though, I just installed the new valve without the aux water pump. The hose positions allow one to easily bypass the Aux pump.

While I've got the cabin-air assembly out and the back of the engine exposed... I noticed 3 sensors on what appears to be a coolant manifold. (in addition to the two intake manifold-mounted sensors). What do they all go to? Should I replace them?
EDIT: Found Em:

05Temperature sensor, water3-POL-2500-OHM1

13621707366$71.05
06Gasket ringA12X15,5 AL1

07119963130$0.09
07Temperature sensor, waterM14X1,51

12621288158$40.02
08ENGINE COOLANT TEMP SENSOR2-POL1

12621747281$31.72
I suppose one is for the HVAC system, one for the ECU's, and another for the dummy COOLANT-TEMP MID message... Anyone ever have to change any of these?

[Fiiz]

Gentlemen, without further ado, I present to you my fix for the HVAC control. It bypasses the transistor that controls the driver's side heater valve. I can't recall exactly what it's doing other than that, but I'd be glad if someone retraced my steps in order to provide more information. I bridged terminals 11&12 at the HVAC control panel (with temp, fan wheels) connector (blue). This can be done by soldering the two terminals together as seen in my photos below, or by simply connecting the two corresponding wires and not opening up the controller at all. Like I said, this has fixed my problem for the past 4 years and I was having the same symptoms as most mentioned in this thread.

Good luck all, hope this helps!!








It looks like I'll have to upgrade from my $5 radioshack multimeter

For the less-electrical-sound mind, what does the soldering achieve?

[Bryson]

the soldering just bypasses a switch in the driver's heater control which puts the system in "full heat" mode. It allows the HVAC system to operate in the normal temperature control range

[Frankie]

Here is some great news for those of us having HVAC issues. If you're like me and have determined the heater control valve is NOT the problem, read this thread. Info courtesy of Max Lumens may illuminate a path (sorry) towards a switch on the front panel controller.

I will be looking at this switch soon...

[Bryson]

Yes, fixing the switch is the right way to solve the problem! Thanks Frankie

[CaifanSC]

so, if I gather correctly....there can now be TWO explanations to the "steaming foot" syndrome instead of ONE?

It used to be that everyone immediately recommended replacing the heater valve when this problem was present. Now, it appears that the small switch in the IHKA controller is just as much the culprit for this issue. So, for the purpose of consolidating a procedure...where should someone start to troubleshoot?

At first I figured that the first step is checking if the heater valves are working by applying 12V to each side...but even if you hear each side clicking as they are supposed to, that doesn't mean the valve is in full operating condition. It could be the case that the valves are damaged and they are not closing/opening correctly. See post/pix:

http://forums.bimmerforums.com/forum....php?t=1671645

So then, is the first step removing the IHKA controller, cleaning the switch and re-soldering? That way, the controller is scratched out as a possibility and, worst case scenario, you do a preemptive fix on the switch. If the problem persists, then you proceed to troubleshoot the heater valve.

If after applying 12v to each side of the heater valve you verify that both sides work you can:

a - (assuming the plastic coolant inlets are still fine and have not snapped broken) repair the heater valve with one of wokke's kits http://forums.bimmerforums.com/forum....php?t=1712949 $59

b - just buy new valve (and matching aux pump just for good measure) aprox $150 for the valve plus price for the new aux pump.

Are these correct assumptions?

[Bryson]

I would start by checking to see if you have 12v at the heater valves with the ignition on, fan on, and HVAC set to full cold. If so, I would point to a failed heater valve, if not, I would point to the switch on the circuit board. Otherwise, yep, two main potential sources to this problem.

[Frankie]

Here is some great news...read this thread...

Well, after pulling my control panel and performing the heater switch test shown in the thread above, I realized it's just a more complicated way of performing a test I've already done. This was my last hope . I now must conclude my problem lies buried in the main control board (mother board), specifically at pin 21, x610, as I feared in this post.

As best as I can figure, there's a bad transistor (or whatever) on the other side of pin 21, shorting the signal and preventing current from flowing thru the driver's heater valve. A complete dead end, literally and figuratively.

[Bryson]

You can try bridging those two pins if you can't locate the source of your failure. It's not the perfect fix, but it's better than what you have now! Plus it is extremely easy to reverse


edit: Just saw your other post, never mind