I have the hot blowers, burnt RCCM issue and have established that most likely the loom is shorting to the bodywork.
Before I pull the front of my car off looking for any breaks or shorts in the wiring loom, can anyone tell me if there is a usual place for this to occur?

thanks.

 

What makes you think it is the wiring loom and not a failed dccv? In my experience with jags. I've owned a bunch of them. The dccv failure is by far more common.

Swap the dccv. If the failure persists. Take a look at the rccm. Do not fix the rccm first bc the bad dccv will blow it up again.

I have had 8 cars with dccv failures. Two of which it affected the ccm. No wiring loom issues. Unless the car was in a prior front end collision the harness should be ok.

Take care,

George

 

I examined the entire system and found 2 burnt tracks in the RCCM, which I have since repared. I believed that a faulty DCCV had caused them but when I ground the DCCV I can operate the solenoids at will.The MOSFETS on the RCCM board seem OK and the DCCV will operate if the switching wires are completely bypassed with 2 core flex directly from the green connector in the dash end panel from the RCCM.

I've measured resistances, voltage and power draw and can only conclude that as the system works perfectly once it is bypassed, that the loom is at fault. It is a very common failure in the UK, a combination of chafing of the wires and corrosive effect of the weather here gives loads of wiring issues on these cars.

I'm taking it to an auto sparky this week to confirm.

 

I assume your tests are based on the car parked and probably not running or at idle.

The simple one would be a) continuity between the dccv and the rccm for all 3 wires. And b) continuity between them.

If you have continuity between the rccm and the dccv, and you have no continuity between the dccv wires. Then the harness is fine.

For the rccm to burn both traces the dccv shorted the MOSFET outputs to ground. They are unfused hence why the ccm traces act as a fusible link.

Now while you may be able to control your dccv via remote wiring. When it's in a car running with the coolant system pressurized coolant may be getting past the valve seals shorting out the solenoids and leading to your electrical failure.

These dccv's fail in two ways. 1) they leak externally. Seals fail and you have a coolant leak. It's a small drip in the winter (dried pink residue on the valve) that turns into a big leak in the summer - valves now closed bc aircon is on.

2) they leak internally. Pressurized coolant gets past the valve seal and shorts the solenoid. THAT'S when they damage the ccm.

If you have not replaced your dccv you need to.

Your repair may allow more current than the trace did, which may lead to a fire (when that wire melts) rather than just a burned trace.

Once again the ccm - dccv harness is easy to test. But to Burn the traces you needed an electrical short.

The wires in the dccv plug will show continuity.

Otherwise it's just a typical dccv failure.

Take care,

George

 

Hi George, I'll do the tests that you you suggest, however my tests are done with the engine running in order to work properly. There is no evidence of coolant leaks around the DCCV, but it could be inside as you say. The system works as it should as long as I bypass the loom, nice 14degree cool air or hot air or both depending on what I choose.

I'm confused about checking the continuity of 'all three wires' from the DCCV back to the RCCM as the power supply is batt+ and doesn't go through the RCCM,only the switching wires do?

In addition to the repair, I have installed 1 amp fusible links in the two switching wires for the DCCV, to protect the RCCM from further overload.

I'm taking it to the auto sparky this afternoon, I'll report back.

cheers

 

Yeah my bad on the 3rd wire. Check continuity to the two control wires dccv- rccm. THEN check continuity between the two control wires and the +12v on the dccv (if those wires are shorted), and make sure you have +12v at the dccv. If all that checks out, it's not the loom.

Take care,

George

 

Or it's the loom but intermittent - this is a rare but known cause. Go for it last.

 

His failure doesn't sound intermittent. In his description it sounds as if my Heat and AC only work right when the wires are bypassed.

The installation of the fusible links was a good idea too. I need to do that with the next control panel I repair.

Take care

George

 

1)There is continuity between the RCCM end and the DCCV end of the wiring.

2)When you say to check continuity between the two control wires and the +12v on the dccv (if those wires are shorted), I'm not sure what you mean? Do you mean the pins on the actual DCCV?

3)(if those wires are shorted) If I short the switching wires to ground, the solonoids operate and I can open and close them as I want. I haven't measured the current draw on each at the time, so it could be that one is overdrawing causing the RCCM to burn? Hence me putting in a fusible link to each wire.

4)The DCCV is getting 12v.

 

Ok part 1 - continuity between the dccv and rccm. great. That is as it should be. - This will show you any breaks in the loom.

Part 2 - The pins in the dccv harness - check continuity between all 3 pins - this will show you any shorts in the loom.

__________________________________________________ ____________

If the above two tests pass the loom is fine.

Part 3 - check the dccv pins for continuity between them - showing an internal short in the DCCV. This MAY not present itself at idle or immediately - until pressure builds up in the cooling system. Another thing may be a partial short showing as a large current draw. Which may in some cases sink the mosfet - in other cases fry the trace.

Take care,

George

 

Hi George
I'm not geting any notification via email, so have just seen your reply.

Multimeter set on 200 ohms scale, the lowest I have.
Part1 - Getting a reading of 1.3 ohms on both wires, measuring the complete end to end of the harness, unplugged at DCCV and unplugged at RCCM end.
Part 2 - Nothing, not even a blip on the multimeter screen. I tested 1 to 2, 1 to 3, 2 to 3.
Part 3 - I'm getting 14 ohms on each switch pin to power pin and 27 ohms on switch pin to switch pin. This and all the test was done with no power to DCCV, engine off and cold, otherwies I can't access the valve or it's pins.

What do you reckon?

 

You just proved the loom is fine.

Part 1 = 1.3 ohms = resistance of the wire. No problem.

Part 2 = No resistance at all - aka no conductivity between wires. No shorts in the loom. The loom is fine.

Part 3 is interesting because it just may have proved you have a bad dccv.

Let's take the formula for current = I = V/R

Assuming 13.5 volts with engine running / 14 ohms = just under 1 amp of current. 13.5 / 14 ths to be exact. Again I assume this is an ignition off engine not running measurement.

Add the coolant in the mix and it probably jumps. Probably frying your RCCM including the 1a fusible links you have added all over again.

Now. What's interesting is the switch pin to switch pin measurement. That almost seems like the solenoids are wired in series. When they should be totally independent. Right side should have not anything to do with left etc.

My money is 98.5% on a Bad DCCV. Replacing or playing with the loom will not change any condition you presently have. You can get the dccv to function by jumping the switched wires to ground (and running an amp or two of current through the wire you added) but it is way out of spec as far as current consumption based on what it was designed for. Which is WHY it burned out the traces in the RCCM to begin with.

Take care,

George

 

Hi George
Thanks for your time on this.
I have been trying to get the front bumnper off all afternoon here, but no luck, all the fasteners are rusted on due to the British weather. It's great that a British car should be designed to rust in this way.

In desperation, I put all everything back as it was and took some voltage measurements at the green connector on the RCCM side of the harness.

Climate control set to LO on both sides, nice cold air and 0.23v on pin 9 and 10 on the green connector pins. That's good.
Climate control set to HI on both sides, hot air and 14.08v on the pin 9 and 10 on the green connector. That's good.

I took some temp. measurements from the vents and noticed that the drivers side is always around 2 degrees cooler than the passenger side.

I adjusted the temp. to LO on one side and Hi on the other, can't remember which. I noticed that the passenger side just got hotter so I shut it all off. Checked the voltages at the dash end of the harness and got batt voltage from the drivers side and nothing from the passenger side. Continuity along both wires is still good and 12v power is reaching the DCCV. The electrical 'loop' is not being made on the passenger wire?

When I did all this the other day, using my bypass wire, it all worked fine. I may not have left it going for as long as I wasn't using a fusible link at the time. If I left it longer, I was concerned the RCCM would have burnt again. I want to do it again in order to prove or disprove a dodgy loom once and for all.

As a side note, ClimateControl.Com is a site that a lot of people have used and I followed their DIY test advice and got all the right readings to show that my DCCV is OK and not drawing too much power. The DCCV should draw 0.6 to 0.9 amps, mine is drawing 0.76 amps, with engine on.

Judging by your reply, a bust DCCV is most likely and so I may have to just buy one and fit it. It could be money well spent. If not, back to square one.

Thanks and I'll keep you posted, if only to tell you that I've sold the car.

 

27ohms is OK. Of course they're wired in series (*)! Here's why

pin1 ---- solenoid1 --- +12V
pin3 ---- solenoid2 --- +12V

(*) but each side of 12V

So ohms pin1 to pin3? Just add the ohms for the solenoids.

 

My DCCV is OK then?

I was going to order one, but rather not spend the money if it needs to be spent elsewhere, such as another RCCM.

Now I'm confused even more.

Do you know why I'm now not getting any voltage through pin 10 on the dashside green connector, which is the passenger side of the DCCV switching wire?
I was getting batt voltage there and on pin 10, the drivers side switching wire. Now it's just pin 10. Drivers side is blowing properly, but passenger side is just getting hotter.
Continuity of both switching wires is good all the way from DCCV plug to green connector. Grounding each of the solonoids is still making a click.

Individually all the components seem OK, but not together?

Checks not done:
Continuity back from green connector to the actual RCCM. Do that tomorrow.
Proper checking of the MOSFETS in case they are broken. How do I do that?

Not sure what to do next, but driving it today was a pain. All the windows open, all vents closed and still my legs getting burned.

 

Well, DCCV was OK when measured. If it's not recently changed it's suspect as it could be leaking internally.

To check the RCCM just move temp up & down and see what the volts do. Remember to have it set on dual zones.

 

I'll recheck it all again today.
The DCCV looks to be original, but not leaking externally. It could be internal as you say.

The dual setting is of interest, the other day during testing, the system was 'working' ie cold on both or hot on both, until I started messing about with having hot one side and cold the other. That's when I noticed the passenger side staying hot and getting hotter. Checking the voltage at the dash panel connector then showed voltage on the drivers side and NO voltage on the passenger side.

This could be showing a fault within the DCCV internal switching, so if I again measure the resistance on all the pins I'll see if it's changed?

If it's just a DCCV change, then I'm a happier bunny.

 

Redone all electrical checks and all are the same.
The DCCV is drawing 0.78 and 0.79 amps, it should be between 0.6 and 0.9 amps. The DCCV is not overdrawing.
The DCCV, if each switch pin is grounded, gives cold air to the side that is grounded. The DCCV solonoids are working.

Still no voltage from green connector pin 10, but batt voltage from pin 9. Both should show batt. voltage.

HOWEVER:
I went to reconnect the plug to the DCCV and noticed the middle pin, power, was bent. I jumpered all three wires acroos from plug to DCCV, to eliminate any pin contact issues. I immediately got batt. voltage from both pin 9 and 10.

I decided to see what would happen to the blowers now. Here's what I got, all results taken from green connector on dash end panel.

On DUAL setting, ie both sides controlled by the driver set to LO
LO - 0.24v on pin 9.
LO - 0.22v on pin 10.
Cold air from both sides.

Dual setting, both sides set to HI.
HI - 14v pin 9.
HI - 14.11v pin 10.
Hot air from both sides.

All good so far.

Take it off of dual zone, ie each side controls their side.
Passenger set to 17 degrees - 0.17v on pin 10. ( actual temp at vent is 35 degrees)
Driver set to 31 degrees - 12.4 v on pin 9. OK, but actual temp is 47degrees at the vent.

Passenger side set to 31 degrees - voltage jumps around from 0.2v to 12.24v on pin 10. Actual temp is 38 degrees at the vent.
Drivers side set to 17 degrees - 0.19v on pin 9. Actual temp is 15 degrees.

Set to dual control on HI or LO, it all works fine. Take it off and choose anything in between and mostly the passenger side goes nuts.

***The outside temp was showing as 10 degrees, when in fact it was actually 26 degrees. It has always been OK before, so maybe a new issue?

What do we all reckon?

 

Change the valve.... There's a REASON you burnt the traces in the RCCM.
DCCV is internally leaking / shorted.

Take care,

George

 

You're gonna rolll your eyes and I know that I should change the DCCV, but if it's not drawing too many amps and is otherwise behaving, I'm having doubts as to whether it is faulty. The DCCV could have been swapped for a working second hand one by the previous owners, but the RCCM had been overlooked?
If it's shorted inside, would I not see an increased draw?