First off, thanks to everyone on for their previous advice and replacing the DCCV valve. I don't know if anyone has posted the internals before...if not, some of the photo show the key internal parts.

When I opened the valve, I had coolant that leaked into the coils section - the exterior metal cans. Upon further examination, a slight coolant leak or coolant over the coils may not be as destructive as everyone thinks since the coils are in a waterproof potted environment that contain the electrical connector. I think its designed to operate with coils exposed to moisture. Furthermore, when you look at the valve assembly, the return spring is pretty weak. At first, I thought my seal was worn out since the plunger was pretty loose, but the return spring doesn't seem to be designed for a tight seal (may explain the tendency to get stuck). Lastly, there is no seal between the top of the plunger and the metal can that covers the coils so if coolant does get past the plunger and fill the coil section, its possible it can leak or seap out. In any case, due to the potted nature of the electronics, it should operate as designed.

Thoughts on shorting out the HVAC controller: The HVAC controller closes the valves with a FET or transistor between the coil and ground. This pull down transistor would have no current flow if it was shorted to ground.
The high voltage is supplied to the middle pin via the B+ buss. The DCCV is isolated from the chassis and lets assume the coolant is at GND potential. If the potted electronics were to fail and let the coolant in, it could ground the coil somewhere between the B+ to the HVAC terminal - where the insulated wires are connected. If it shorts near the HVAC terminal, the current between B+ and the coolant ground would keep the coil energized, the current in the HVAC controller would be zero and the voltage zero when Lo (no way to damage trace). On Hi, the FET would switch off, current would still be zero but the voltage would not go up to B+ but no way to over current and damage the trace). If the coolant shorted it out near the B+ terminal, it would draw more current thorugh the B+ line that may blow the fuse. If not, when HVAC goes to LO, coolant has shorted the line, terminal should see 0V and 0A (no PCB damage). On Hi, FET is off, so 0V and 0A (no PCB damage). In short, the controller has a pull down FET so if the terminal is shorted to ground, the current is reduced not increased. I think the potted nature of the coil and the pull down design of the controller suggests that its unlikely that the coolant will short anything out and even if it does, it will not cause more current to flow into the controller to damage the trace.

On the other hand, if the epoxy insulation on the wire of the coil is substandard and breaks down (usually due to excessive heat), the resistance of the coil will drop which will increase the current seen at the controller terminal leading to over current failure. This failure mechanism can happen in the unlikely event that Bosch is using epoxy that dissolves with coolant. Aside from that, I don't think seeping coolant will lead to a blown controller...there is another failure mechanism out there.

So contrary to public option, IMHO, 1) leaking coolant may not imply a DCCV thats about to fail and 2) leaking coolant doesn't cause high current and the controller leading to a failed PCB trace

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Unlike most, when HVAC is showing Lo-Lo one side is hot the other is cold, in my case, HVAC is showing Hi-Hi, driver side is cold, passenger is hot so valve may be stuck open. Measuring the pins 9 & 10 on the side of the dash showed on off impedance of 32 ohms (two 16 ohm coils in series), on voltage of 0.26V and off voltage of 13.56V. The on (active low) voltage is the same on both side so I don't think this coil is pulling more current then normal else the voltage would rise due to the Rds of the pull down FET.

So after replacing the DCCV, on Hi-Ho, the driver side is warm and the passenger side is hot...any suggestions on where to look next. I assume that on Lo-Lo, Hi-Hi, all of the temp sensors are bypassed. The voltage and current measurements show that 1) the controller is working and 2) the wiring harness is not compromised. Would be nice to get this fixed so car can heat up quicker on those cold mid 50F winter mornings when winter finally gets here.

 

I haven't managed to work through that properly, sorry, but aren't the coils separate? So, never in series? I thought each was operated individually so you'd have two each of 16 (or however many) ohms. If you considered both then I suppose 8 ohms, i.e. parallel not series.

 

ccc, you checked the vent discharge sensors correct? they are both on the evap box one on each side.

 

Each coil is 16 ohms. The first coil is between pin 1 and 2 on the DCCV and the second is between pins 2 and 3 (they share a common terminal). When connected, pin 2 is tied to a switched positive rail. Pins 1 and 3 on the DCCV maps to pins 9 and 10 on the side of the car. WIth the power off, measuring the resistance of pin 9 and 10 will measure the resistance of both coils in series so its 16+16=32 ohms. If you short pins 1 and 3 then measure the resistance from 2 to 1 or 3, then it would be 8 ohms.

 

No I haven't, I've read that the HI-Hi or Lo-Lo setting bypass the sensors. Perhaps its just the cabin sensors not the protection sensors. Will check these right away. THey should be the same so I can just swap them to see if there are any changes?

 

That is correct my 02 was acting erratic (random cold to hot in different positions )

Changed out dccv twice changed out CCM finally I changed the evap sensor and the 2 discharge sensors And voilà fixed. Should have been a $60 fix which cost me $500 in parts.

(I had also replaced the aux coolant pump. )

 

interesting, but Ive yet to see a blown Ac control module for the 2 DCCV drivers that didnt have a leaking DCCV. Ive seen lots of leakers without damage but never a bad module without a leaker....hypothesis to you CCC

 

Well the sensors made to the top of my do list. Did you ever have erratic behavior when the temp was cranked up to display hi instead of the temp setpointor down to lo? Based on info from this site, I did rev the engine at 3500 rpm for a while and same problem so I am assuming the aux coolant pump is still ok.

 

Ah, OK. I didn't see that you were measuring them that way.

When you say "pins 9 and 10 on the side of the car" what do you mean?

 

Its hard to get to the connector of the DCCV without serious disassembly. On the forum a DCCV article mentioned that you can open up the panel - on the driver side (US) of the dashboard with the doors open - to access a few electrical connectors. On the one that is closest to engine, pins 9 and 10 are connected to the DCCV. Through the shell, you can contact the crimp end of the brass pins without disconnecting the connector. This allows for in-situ monitor of the DCCV.

 

Mafioso, where are the evap sensor and two discharge sensors? Is the evap on the airbox above drivers right knee and discharge sensors on dash in front of driver and behind glove box? Are they difficult to change?

 

By your logic each coil should show resistance of 16 ohms when measured individually between pins 1-2 or 2-3. The coils operate independently of each other, They just share a common +12v supply rail. No need to short out the other sets of pins.

I still think the electrical failures are in fact coolant related. First of all your pics show a clearly failed DCCV, that was externally leaking. There should be no coolant outside the seals. I think yours is one of the lucky ones that failed with an external leak. From what I have seen the failures take two modes.

1) Leaking externally outside of the casing. This is what yours was doing, and it's a failure of the seals that the plunger of the coil goes into, allowing coolant to escape out, when the DCCV is CLOSED. Coolant is under pressure, and the seal can't hold it, and it seeps past the seal, outside, and past the valve to an external leak.

2) Internal leaks INTO the coil, probably due to a failure of the plunger shaft seal allowing coolant to go up and enter into the coil. Assuming the coolant is in fact conductive, what I think is happening is it's shorting the B+ rail to the ground output of the transistor. Most of the time the transistors don't fail, BUT you burn up the ground traces, because too much current is going through them. Basically what happens is you create a dead short at the output of the transistor, and the trace acts as the fuse (because it's the weakest link), and fries the trace.

Transistor failures are more likely due to internal coil failures (or flooding) that show low resistances rather than coolant caused dead shorts (which blow the trace) and overheat the transistors.

George

 

There are 3, on the pass side unlatch the glovebox and let it hang you can fit your hand on the evap box, and its a connector with 2 wires,

On the driver side look on the evap box above the accelerator pedal there is 2 sensors.

 

CCC:
Thanks for the info but as Brutal says you are missing something here?? The facts show the failure of a DCCV can and does take out the climate control module. Two different failures. Either burning a transistor out or a trace on the board. No one has reported a climate control module with either of these two failures that DID NOT also have a DCCV failure.

So they are related but I am not sure why??
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#1 Agreed, just wanted to point out previous post if you wanted to put them in parallel, there is no reason to do so. Each individual coil is 16 ohms.

#2 My never leaked, it was stuck open. The coolant on the DCCV was from the thermostat housing where it was leaking between the pressed in steel insert and the al casting. Its a $1200 part but seems like the $6 JB weld is doing the trick.

#3 My the seals failed and let coolant into the chamber with the coil but did not leak out - chambers and coil assembly was wet when opened.

#4 My first post was written in haste so sorry if its not clear, the main point is the the coil, electrical connector is potted in plastic which if not cracked is hermetic and should be water proof. I don't think coolant into the coil area means the electrical winding is wet, only the waterproof plastic housing. I would be great if someone had a DCCV that they believe is shorted due to coolant and can measure resistance from the coolant to any of the three pins. That would imply a potting failure in addition to the coolant leakage. If its not cracked, the coils are waterproof or coolant proof. In other words, coolant leaking past the seal doesn't mean a coil short unless something else failed in addition to.

#5 My point is a short will not blow the trace to the two pull down transistors that controls the DCCV (pin 1 and 3). Any short at anypoint along the coil will reduce - not increase - the current seen in the pull down.

#6: I don't know where the DCCV B+ (pin 2) is connected too.
a) If it is connected to the control module then it will cause an overcurrent condition to take out the weakest link.
b) It was my understanding (perhaps incorrect) that its connected with the aux coolant pump to a common fuse that is not the same as the controller. Also, if the blown PCB trace would have open circuited the B+ pin, then the observed hot one side and cold (assuming one side switches, other not vs physically stuck) can't happen. Furthermore, why would anyone provide pull down FET for switching pins 1 and 3 and add another an additonal high-side FET to switch the common mode terminal?

#7: Don’t really understand your different modes and its electrical implication. For the coolant to short out electrically, here is what has to happen

X1) plunger seal needs to fail and allow coolant to contact coil module or external
leak to the contact the coil module – say near the connector
X2) potting on coil module needs to mechanically fail to let the coolant inside module
X3) need to eat through the epoxy coil wire to get to the conductor or make it all the way to the connector housing where the epoxy is stripped to solder to connector

As long as the coolant is continuous then grounding anypoint from the top from pin 2 to pin 3 along the coil will reduce the current seen by the pull down FET

 

Re #6:
Electrical diagram may be wrong but (for 2002.5MY I think) shows on fig 06.1 DCCV pin 2 goes to fig 01.2 and via a splice/connector or two to fuse F32 (a batt+ feed, not sure whether via a relay but doesn't matter). So, pin 2 isn't via an FET or such like.

Good pics, btw - thanks!

 

i know lots of acronyms but what are you reffering to as FET federal exise tax??
on the B+ it and the ac compressor clutch share the same fuse. and is ignition switched hot. the CCM(climate control mdoule) provodes ground signal to the valves to close them, theyre normally open. now if you get coolant up into the coils and the pins both positive and negative that feed each 1. youre gonna feed B+ to a modules ground circuit. most module circuity is not a high or or for that matter much able to handle any amperage. This is a prrimary reason to never use a test light, but a DVOM(digital volt ohm meter) to check circuits. a dvom is very low impedance and safe to pin cuircuits. Now if you have a cross short on the CCM ground circuits to battery power, when theyre switched to ground(active) you now have a fusible link that isnt supposed to be 1. Hense the burned circuit board in the CCM on either 1 or both legs going to the DCCV coils. to me it doesnt matter so much as where of even why, but all blown CCM's have a leaking DCCV, but not all leaking DCCV's have blown CCM's, its just a matter of time. theres a great many things I deal with on a regular basis that there NO WAY that should happen that way, but yet it does and I have to fix it. Just recently ablind spot monitor issue that shut down the CAN network, nothing wrong the the CAN network, but ended up finding a open circuit in the mirror icon. Jaguar said theres no way that can happen, yes maybe not supposed too(should have given a code in the blind spot monitor modules not shut them down) but yet it did and there was alot of wasted time checking stuff only because
"that cannot happen, it doesnt work that way" was said repeatadly. Same issue I have with a 2011 XK lic plate light going out that are module driven...time will tell on that 1.

 

FET = field effect transistor IIRC. It's a (semiconductor i.e. transistor) switch.

 

Assumption 1: DCCV valve leaks, coolant shorts coil, shorted coil increases current leading the controller PCB trace failure.

My theory: 1) Coils and connector are in waterproof housing so its by design robust to leaks. 2) A short would require a seal failure, a potting housing failure, and a failure of the epoxy insulation - less likely - I think most people assumed the coil of wire would be directly exposed to coolant if it had an internal leak. Will go as far to say, it may be designed to operate with an internal leak. Requires multiple consecutive failures before you see the effect. 3) Controller with pull down FET is robust to shorts - it will decrease, not increase the current seen by the pull down FET. My main point from the deconsturction, is the DCCV design is more robust to electrical issues due to leaks.

I'll bet most good DCCV have some internal leakage that will cause the coil assembly to be wet

Assumption 2: The impedance of the coil can change leading to higher currents when DCCV is energized

If this happens, the drive current will increase and the FET or PCB can be damaged. This may or may not be releated to the coolant issue. Coils can fail if the actual temperature is higher then the design range - wears down the epoxy and the coil impedance drops. Friction and vibration will wear at it. In AC applications, the small mechanical motion when the fileds energize can reduce it. Defect in insulation applciation can cause it. If a small amount of moisture gets in (say coolant), and shorts pins say 2 and 3 or part of the coil but not enough to ground it, then higher currents can result.

People have measured units with low coil resistance

Assumption 3: Electrically value is ok, plungers are mechanicall stuck

I think my fell into this category

Assumption 4: Just got a leak somewhere but no electrical issues

Damm seals


So lets conclude that 1) DCCV mechanical seal design is poor so there is a high number of leaks, 2) with a potted coil design, it should be more robust to coolant then first though, 3) Just a short to GND will not cause over current, 4) there is another TBD failure mechanism that causes high current draw in the coil - call it failure X - may or maynot be related to coolant contamination.

Are they a lot of leaking DCCV valves that don't have any controller issues - no failure X (yes)

Is there a good chance that a failure X valve will be leaking (yes)

Working but not leaking DCCV with wet coil modules - I think so based on the design

Its more then luck that the number of leaking DCCV doesnt = # of blown controllers (yes)

Can you have a controller failure with a non-leaking DCCV? (possible)


I do think the DCCV failure can take out the module but not necessary a leak. Need to figure out the root cause of failure X. My thoughts is that there are too many leaking DCCV out there and a leak may not necessary call for a $85 part to be replaced in a PIA location to protect a $2000 computer.

If we could figure out what caues failure x, a better test may be devised. For example, measuring the resistance between pins (9 and 10) and (9 to gnd) and (10 to gnd) may be an more reliable test. I don't have access to a module that caused the controller to fail but if I get sent some, I be happy to do some F/A on it.

 

Sorry, I have a 2004 STR and use the newer 3 hose DCCV, I think the older onles use a 5 hose DCCV. Sorry for the confusion.