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Btt for further reading. I agree with the initial post and im trying to work out the failure mechaism. But like the OP said, I cant see how the RCCM can over current since it applies a ground. Somehow, the 14v ystem voltage is getting on the ground pin and shorting out the trace in the RCCM
Negative current smokes wires just as bad as postive. Its unfortunate that it was not relay triggered instead of direct negative triggering. 2 ways to kill it. Short to power internally of the negative trigger from the ccm and over current with the windings of the coils pulling too many amps and smokes the very thin circuit in the ccm
I agree that is true but the current source is the main power bus and the return is throught the pwa in the RCCM. The DCCV is a coil of wire with (apparently) 16 ohms resistance.
So in order to draw more current, antifreeze has to be less than 16 ohms across the power in to ground connection.
Do you think antifreeze/water would measure less than 16 ohms if you measured some antifeeze in a cup? I wouldnt think so but I will try it
I agree that is true but the current source is the main power bus and the return is throught the pwa in the RCCM. The DCCV is a coil of wire with (apparently) 16 ohms resistance.
So in order to draw more current, antifreeze has to be less than 16 ohms across the power in to ground connection.
Do you think antifreeze/water would measure less than 16 ohms if you measured some antifeeze in a cup? I wouldnt think so but I will try it
I don't know but have replaced a whole lot of them and ccm's over the years for coolant leaking down into them from the reservoirs.
So in order to draw more current, antifreeze has to be less than 16 ohms across the power in to ground connection.
Do you think antifreeze/water would measure less than 16 ohms if you measured some antifeeze in a cup?
Put down the calculator. Turn around. Walk away from it. Don't look back...
Calculations for resistance values and current flow aren't always so straightforward. You've got pulse width modulation going on, with power to the coil rapidly switching on and off. That means a magnetic field rapidly building and collapsing, which induces counter EMF.
Then consider coolant typically picks up some metallic content, for just a teensy bit of conductivity. Good luck measuring that unless you've got some lab grade equipment.
Next factor in how the coolant may partially break down the thin varnish insulation of the coil windings. Might be fine when cool, but worse with heat. No idea how to calculate that.
Put it all together and any calculations we mortals can make would be essentially worthless. Excess amperage is what damages the circuit board. It's far simpler and WAY more accurate to just measure the actual amperage of the circuit under load, versus trying to extrapolate based on a resistance value.
Put down the calculator. Turn around. Walk away from it. Don't look back...
Calculations for resistance values and current flow aren't always so straightforward. You've got pulse width modulation going on, with power to the coil rapidly switching on and off. That means a magnetic field rapidly building and collapsing, which induces counter EMF.
Then consider coolant typically picks up some metallic content, for just a teensy bit of conductivity. Good luck measuring that unless you've got some lab grade equipment.
Next factor in how the coolant may partially break down the thin varnish insulation of the coil windings. Might be fine when cool, but worse with heat. No idea how to calculate that.
Put it all together and any calculations we mortals can make would be essentially worthless. Excess amperage is what damages the circuit board. It's far simpler and WAY more accurate to just measure the actual amperage of the circuit under load, versus trying to extrapolate based on a resistance value.
Well im still curious. This is what I do for a living for NASA and other space satellite companies. I investigate electronic failures and determine root cause and corrective action.
It may be the insulation breaking down and causing the coil to short. Very possible failure mechanism. But it also may be the trace on the circuit board is designed undersized so it cant handle the nominal current very well. It may be that the pwb is at its maximum rated current flow due to poor design and they all just burn out over time and temp.
In any event, I will be installing protection devices in place of the traces in the rccm I just bought
Well im still curious. This is what I do for a living for NASA and other space satellite companies. I investigate electronic failures and determine root cause and corrective action.
It may be the insulation breaking down and causing the coil to short. Very possible failure mechanism. But it also may be the trace on the circuit board is designed undersized so it cant handle the nominal current very well. It may be that the pwb is at its maximum rated current flow due to poor design and they all just burn out over time and temp.
Don't forget that some don't seem to have any PCB damage but the semiconductor device (power transistor, I guess) is dead. Feels another reason to suspect over-current and quite a bit of it.
well im still curious. This is what i do for a living for nasa and other space satellite companies. I investigate electronic failures and determine root cause and corrective action.
It may be the insulation breaking down and causing the coil to short. Very possible failure mechanism. But it also may be the trace on the circuit board is designed undersized so it cant handle the nominal current very well. It may be that the pwb is at its maximum rated current flow due to poor design and they all just burn out over time and temp.
In any event, i will be installing protection devices in place of the traces in the rccm i just bought
another thing that takes them out and may also pull too much current is the valves when they stick. Theyre normal open for safety(you want heat and defrost so thos are failure defaults to clear a foggy windshield) they do stick open and or partially open and trying to seat would pull more amperage than designed. Or maybe was designed that way. over the years i have encountered a lot of parts that fail at a point that almost seems like it was designed to fail at that point.
Not a car manufacturer issue but part supplier. After warr you want to move parts you had to sell to end use manufactures cheaply.
This is a cool device. Its actually a switch for the ground triggered circuit. It can handle 3A nominal. And has a max rating of 30A!!!! So its pretty stout.
It also has short circuit protection AND its safe from ESD hits up to 2000v!!!!! So its unlikely to be killed by a short in the coil.
Im really starting to think the PWA trace is just way too undersized for the application. Not sure how the coil resistance changes to less than 10 ohms. But heres the math.
At 14v and 16 ohms coil resistance the current is 0.875A. To get to 3 amps you need a coil resistance of 5 ohms or so. At a dead short youll get 10 amps before the fuse blows but the trace will have fried by then.
I was considering using a 10 ohm 10W resistor to limit the current to 1.4 amps if the coil shorted and installing those resettable fuses as a secondary protection device. That way if the coil shorts, current is limited to 1.4A. The 10ohm resistor drops the voltage to the coil though. With a 16ohm coil resistance, the 10 ohm resistor may cause the coil not to pull in the valve. I will have to check.
Not sure how to handle this yet. Theoretically the Smart low side switch doesnt need current limiting and with the board traces bypassed its probably not needed!
I was considering using a 10 ohm 10W resistor to limit the current to 1.4 amps if the coil shorted and installing those resettable fuses as a secondary protection device. That way if the coil shorts, current is limited to 1.4A.
How about a simpler upgrade? Per this, a good DCCV draws up to 0.6 to 0.9 amps per side:
I've thought of a simple inline fuse in the harness to the DCCV. You could put one fuse in the single power feed wire, perhaps 3 amps to cover both sides. Or put separate fuses for each side, maybe 2 amps or so. What do you think? If the fuse were to blow, access should be a lot quicker than removing the control module and opening it up.
Yes an inline fuse would work but where would you install it. The connector for the DCCV is buried and hard to get to. Up top youd need to deconstruct the wiring harness to tap into it.
A resettable fuse would be ideal. Like in my photos!
And you could put them anywhere but why not just do the mod to the RCCM and cut the trace?
I bypass the board like you did too and solder directly to the bars. I had 1 that had opened past the normal spot so i started going to the solid bars for the pins so it would be a more robust repair. I think just the larger wires give it all the protection needed. But overkill is never a bad thing either
A resettable fuse would be ideal. Like in my photos!
Interesting, I've never messed with that style. From what I've been reading, that type automatically resets? I was thinking you'd have to open up the module to manually reset them.
Could these doohickies open and reset all day long, a current regulator so to speak? In other words, if I tried to pump 1.1 amps through a 1.0 resettable fuse, would it rapidly cycle and limit current flow to 1.0? Or is the cycle much slower, with long periods of an open circuit?
Yes an inline fuse would work but where would you install it. The connector for the DCCV is buried and hard to get to. Up top youd need to deconstruct the wiring harness to tap into it.
A resettable fuse would be ideal. Like in my photos!
And you could put them anywhere but why not just do the mod to the RCCM and cut the trace?
yes, i did that, every thing worked fine, now the AC fan comes on and flattens the battery when the vehicle is all locked up, haven't been able to find out how to fix it, but your instructions were a great fix, thanks
yes, i did that, every thing worked fine, now the AC fan comes on and flattens the battery when the vehicle is all locked up, haven't been able to find out how to fix it, but your instructions were a great fix, thanks
so I’m revisiting this post I was a part of sometime ago because I was still having periodic problems with my air-conditioned car getting nothing but heat after driving for a while. If i shut it down came back sometime later, the air-conditioning would be perfect. No heat like before. But then after driving, for a bit id get the same problem- super hot heat on both sides.
I didn’t think it could be my climate control module because ccm had those resettable fuses installed by Jaguarclimatecontrol.com. Well, i think those resettable fuses gave me a false sense of security. I think.
I went through the whole system again earlier today and measured all sorts of values and made sure my voltages, currents and resistance values were correct and they appeared to be just fine.
I was worried because when I started having this problem, I replaced my DCCV. But I had installed a cheap $30 DCCV despite all the warnings about potential failures if I don’t get the OEM Bosch valve.
well, I went out and I measured the resistance of the solenoid coils in the DCCV and they were right on the money at 16 ohms apiece and 32ohms through both coils in series measured at the climate control module connector. I even measured the same value when I went to the FC4 chassis harness connector on the side of the instrument panel by the drivers door ( left side.)
I had correct system voltage at the center terminal on the valve so there’s only one more failure point that could’ve been causing my periodic heat. That’s inside the climate control module.
I said earlier that the low side switch inside the climate control module is extremely stout and I still believe it is. It has a 2000 V ESD protection. Overcurrent protection short circuit protection, 30 amp max capability for short period of time. Also usually when something like that burns out it burns out forever and doesn’t repair itself, and my problem is definitely periodic and it takes a while for it to happen after you start the car up so that points to something that trips and then goes back in service-like a resettable fuse maybe?
so that only leaves those damn resettable fuses shown earlier in this post. when I went to pull the data sheets on those resettable fuses, I found out something interesting- they don’t sell that value anymore. The parts that I have were marked G0 or 60. Its hard to make out. I believe it’s G0.
Looking at the little fuse catalog for PTC resetable fuses shows that the smallest value they sell now is marked G2.5, which has a 2.5 amp nominal current rating with a trip current of 4.7A. and that made me wonder if G2 .5 means 2.5 amp hold current and a 4.7A trip current, what the hell does G0 mean? How can they have a resettable fuse that has a 0A hold current? I sent an email to Little fuse to ask them about the specs to my devices and when I get an email back I’ll let everybody know what they say.
But in the short term, I am going to remove those resettable fuses and just jumper the burned out traces with a wire straight from the low side, switch straight to the connector pens and call it a day.
still interesting that nobody has found the reason for these traces to be burning up the way they are. I’m just going to assume that the traces on the climate control Module are just way under size for the potential current that can flow the resistance of the solenoid coils is between 13 and 20 ohms each, and as I said earlier, each of my coils appeared to be at 16 ohms individually or 32 ohms in series. So I’ve got about .85 A of current flowing, but if you quit resistance went down to 13 or even 10, you would get over one amp. Up to possibly 1.4 A at 10 ohms coil resistance
i’ll let y’all know what I find. Hopefully jumping straight to the low size switch fix my problems and if I hear back from Little fuse, I’ll let everybody know what a G0 resettable fuse trips at
The second the last column shows the part markings and you can see it starts at G2.5. so what is a G0?
Yes the only explanation I have read from people who claim to know circuit design is they (Jaguar Designers) took the easy way out. The design did not take into account the large current that will occur when the DCCV shorts out. Now to be fair I don't think Jaguar was planning on the DCCV having an almost 100% failure rate either. And again Jaguar build none of this so we can blame it on the suppliers too? But again they build to spec for their clients demands.
So if the DCCV's did not fail so often we would never see the CCM and RCCM failures either? Maybe a chicken and egg situation?
I don't know but I will say the sooner you catch a bad DCCV the less likely you are to burn out the modules.
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08-26-2012, 12:15 PM
over the years i have encountered a lot of parts that fail at a point that almost seems like it was designed to fail at that point.
