Thanks very much to VDPBlue, Paul Mason, GlendoraMike and Brutal, I also fixed my faulty blower. Just thought of posting a few thoughts that may be helpful to others.
1. Removal and Re-assembly of glove box
For me, this was by far the messiest part, even armed with the shop manual instructions that GlendoraMike posted.
To start with, the trivets under the trim just need to be pulled out with a set of pliers (the central bit). Then remove all the other screws / bolts as per the shop manual instructions. Afterwards, one issue I had was the glove box simply would not drop down and was held up by the lead to the light on the side (left side on a right-hand drive, and right side on a left-hand side). You can turn the bulb by half a turn to remove the bulb and attached lead and the glove box should drop down. Another issue was that I couldn't remove the lead to the cigarette light / charger insider the glove box, as it was very tight. In the end I realised It is not necessary to remove this. Reassembling the glow box was also a bit messy, but persevere and hopefully you will manage without breaking anything.

2. Remove and test Unit
After the glow box is off, removing the blower control unit is very simple. As GM said, you have to remove the screws first before taking the unit (with heat-sink fins) off the duct. Then simply unplug the lead. Before replacing it, you should try to at least see if the fault is with the thermal cut-out. As Paul Mason says, there is a plastic back opposite to the fins that can be prised off. Then you will see a PCB. Without de-soldering anything, check the connectivity of the fuse with a multimetre. If it is open-circuit, the fuse has blown. If it shows a short between the fuse terminals, the fuse is fine, but the MOSFET may be faulty (see below).

To remove the PCB you need to de-solder three leads to a MOSFET that is screwed down underneath the PCB. Try to remove these quickly to avoid any heat damage to the MOSFET, and a solder sucker is invaluable here. Now you should be able to remove the PCB. The MOSFET is a power N-channel MOSFET that I'm guessing basically acts as a chopper with varying duty cycle. You should do a quick check to see that the NMOS is not faulty. This link explains one way to test a MOSFET with a multimetre: Testing a MosFet
If it is, you can probably find a replacement by searching online for the transistor number.

The thermal fuse is meant to protect this NMOS, and you should be careful in putting the NMOS back, and make sure that the white gel ensures a good contact between the transistor and the heat sink.

When soldering items back, try to do it quickly and cleanly. The thermal fuse is rated at 110 C, while solder typically melts at about 180 C. I was a bit worried that I would blow the fuse when soldering it back, but I left the long leads untrimmed (to dissipate as much heat as possible as far away from the fuse as possible), did a quick solder, and then trimmed the extra bits of the leads, and it worked first time.

My field is microelectronics, and to me testing and replacing the fuse was a doddle, and fiddling about with the glow box disassembly and assembly far messier. However I'm convinced I saved myself at least £500, and when everything is back and working properly, its a great feeling!

 

Hi serendib,

Welcome to the Jaguar Forums! It's great to have you with us.

Thanks for the report on your blower control module repair. For the benefit of others who may be visual learners, the photos at the thread below may help illustrate some of your instructions:

https://www.jaguarforums.com/forum/xj...t-sink-126502/


And since we're a friendly group, please visit the New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum and post an introduction so we can learn something about you and your Jaguar and give you a proper welcome.

Cheers,

Don

 

Cheers Don, and I have to confess that I did not see past the first page on the thread, and I realise that many folks have posted many useful bits of information that make my post entirely redundant. The link in your post has far more information than mine and is a much more comprehensive post.

 

Did everything glendoramike suggested and now my blower is working on my 04 XJ8 - thx!

I got my part from RockAuto.com - part# ru855

 

Hmmm....Did a fast check today as to why the blower on my 2005 Jaguar XJ8L suddenly stopped working two weeks ago, and discovered quickly enough that the module is faulty. Well, I removed the two (horizontally positioned) 8mm hex nuts on the glove box bottom, and the two black (vertical positoned) torx screws on each side of the glove box bottom (along with the little phillips head screw on the driver's side). Not sure what other screws that I will have to remove to get the glove box out, but I may have to consult the shop manual. Anyone have any helpful tips? As soon as I can get the module out, I'll check out the thermo fuse on the circuit board. If the thermo fuse is open, I'm intending to replace it with a regular GMA 2A fuse.

 

Rickkk,

It was about four years ago that I went thru this drill - the only "interesting" screw I remember: My glovebox (also 2005 XJ8L) has a power outlet (a la cigarette lighter plug): I had to remove the plastic housing for that outlet to find the last screw holding the glovebox.

Ray

 

Hi Rickk,

I may be confusing our '04 with our '93, but I think there are some screws along the top upper edge of the glove box opening. The instructions are given in the Workshop Manual, which you can download in six sections from the 'HOW TO ' quick links thread on the home page of this X350 forum. Working our glove box out required a little twisting and effort because the lamp housing on the left side didn't want to come free of the console. You may need to disconnect one wiring harness, but on our car most of the wires to the glove box were long enough that I could just lower it to the floor and let it rest there while I worked on the module. At the thread below are photos of my module rebuild with a new heat sink with longer fins. Note Tom P's post about a source for a suitable heatsink:

https://www.jaguarforums.com/forum/x...t-sink-126502/

Regarding the idea of replacing the thermal cutoff with a GMA fuse, I would be curious to know your reasoning. The thermal cutoff is a heat-sensitive device, while a GMA fuse is current-sensitive and will not provide the same protection. The real problem with the modules is that the original heat sinks were underengineered and did not provide sufficient cooling. I suppose it might be possible to find a power MOSFET with similar electrical properties but a higher temperature rating and then use a thermal cutoff with a higher fusing temperature, but I haven't done any research on that possibility.

Cheers,

Don

 

Thanks for the tips guys! My reasoning for the GMA 2A fuse substitution was that the blower was likely working since the vehicle was new. Moreover, the blower was functiong all the while during the earlier part of that day (after Easter). A few hours later (after a cold start), the blower simply failed to come on. Assuming that the thermo fuse did blow, I might have surmised that it opened up from 'fatigue' (so I was just opting for a 'quick fix'). Whatever the case, the module evidently wasn't what one would describe as being 'reliable'.

However, assuming that the thermo fuse did blow, a sensible repair would be to at least replace the MOSFET, and to install a larger heat sink as well. If I should have the time, I'll check for a n-channel MOSFET with a higher rating than the original. Thanks!

 

Well, despite the blazing heat outside today, I managed to remove the glove box at my folk's place today, and also the blower control module. I will take the module apart at my place tomorrow, but it's hard to imagine that there's room for any sort of electronics inside that little module. Wow, after all of the fasteners were removed, it seemed that I had to struggle a bit to get the glove box finally out of there.

In the meantime, I placed some rags on the passenger floor so as to prop up the glove box, relieve tension on the electrical wires and to keep the glove box door shut.

Edit: I removed the module cover a few minutes ago, and although I didn't desolder the thermo fuse from the circuit board, it appeared that the fuse was OK. Tomorrow, I'll have to examine that circuit board further. Perhaps I might find some cold solder joints, or that the MOSFET simply failed without the thermo fuse opening up.

 

Well, after performing a thorough examination of the blower control module yesterday, the only thing that I found which could have prevented the blower from working was that there might not have been enough solder on the underside of the circuit board to make a firm connection with the four male blades (which plug into the female receptacle). The blower is currently working (thus far). Unfortunately, the glove box door won't close now so I may have to take the glove box out again to ascertain the problem.

 

Well, I finally forced myself to work on the glove box today, and the glove box door is opening and closing fine now.

Now it seems that the popular consensus is that the N-channel MOSFET inside the blower control module needs a larger heat sink, but I'm not so sure. In fact, I suspect that there may not be a good enough solder joint between the four male blades and the circuit board (specifically on the board underside). If that occurs, the arcing could draw an excessive inrush of current which may cause the MOSFET to overheat, and thus open the thermofuse.

After I thoroughly examined the blower control module from my 2005 Jaguar XJ8L a couple of weeks ago, the only thing that I could possibly find wrong was that the four male blades may have needed some more solder on the circuit board underside. After applying some more solder to those areas, the blower fan has been working fine since then.

 

Rickkk,

For the record, I rebuilt our module with a new MOSFET, thermal cutoff and heat sink with longer fins and didn't touch the solder on the connector blades, and our module has been working for a couple of years now, so perhaps there are multiple causes of failure? The acid test will be when you're idling in stopped traffic for prolonged periods on a 90 degree F day. If your module survives that, you're probably good!

Thanks for the reports - very helpful info!

Cheers,

Don

 

Thanks for the reply Don! As I mentioned previously, I did perform a thorough examination of that module.

In regards to the N-Channel MOSFET, I first checked the transistor with a modified curve tracer, and it checked OK. However, I would strongly advise not to use a curve tracer with the MOSFET as most tracers may harm the device.

I then connected the MOSFET to the diode check of my digital voltmeter, and it registered 0.42VDC (which would be totally in the ball park).

The best check by far would simply be connecting the MOSFET to a test stand. As shown in the attached diagram, a 100,000 ohm resistor was connnected between the gate and the source. Then, a 9VDC battery was connected to the gate and source. At that point, the ohmmeter read zero ohms betwen the drain and the source (which obviously meant that the transistor was conducting). Whenever the 100,000 ohm resistor was momentarily shorted, then the ohmmeter would read open (no conduction from drain to source). In using this test, the MOSFET of my blower module checked out perfectly.

I also checked the 2.2uF 50VDC capacitor on the circuit board, and it was OK. Moreover, all of the 1/4 watt resistors were in good shape as well.

Afterwards, I then focused on the soldered connections on the circuit board. What I couldn't help but notice upon inspection was that one pair of the male blades was not set quite as deep into the circuit board as the other two, and that in itself could have been where the problem originated. Viewed from the underside of the circuit board, all four of the male blades even seemed to have lacked solder. Well, after applying additional solder to those deficient areas with my soldering gun, I then proceeded to check it out on the car. The heater fan came on instantly and flawlessly.

I hope this helps.

 

Drat! After leaving the car outside for four consecutive days in the cold weather, the blower fan suddenly quit while I was driving the 2005 Jaguar XJ8L down the expressway today.

When I checked out the blower control module in March, I was quite sure that there was nothing wrong at all with any of the components inside that module (including the N-channel MOSFET). I wonder what gives here? It seems that the cold weather brings this condition on.

 

When Jaguar realised that the failure rate of the BCM was high

they changed the design and produced them with longer fins.

However in the data sheet of the Mosfet which I used it

said something like "not to be used in safety critical applications

eg traffic lights"

 

Perhaps the N-channel MOSFET that Jag was using in their old design wasn't meant for that application (despite the heat sinks). What's likely happening with mine is that the MOSFET device simply fails to conduct in cold conditions. I wonder if they're using a different transistor now in their new design?

 

Well, I elected to order another blower control module on-line from a Jaguar dealership on eBay (which ran me about $210) last week, and I installed it in my 2005 Jaguar XJ8L today. You know, that new module looked exactly like the one that I took out (so perhaps this was changed yet again before I even acquired the vehicle?).

At any rate, the blower motor now works (for now). During the process of reinstalling the glove department, a couple of retaining clips did drop to the floor. I think that those likely went to the rear of the glove department where the two torx screws are fastened (as I was unsuccessful in fastening those screws back in). Sometime when the weather warms up in the Spring, I'll take the glove department back out, and reattach those retainers. In the meantime, I'll try to keep warm.

 

Well, I finally got around to getting the glove box properly secured earlier today so everything looks good. The only thing left to do now is to find out why the cigarette lighter below the radio keeps blowing the 15A fuse.

 

Hi Rickkk,

That sounds like it is almost certainly due to a short, which is easy to cause when moving wires around.

Hope it's easy to track down. Unfortunately it may mean pulling the glove box again...

Before you do, check the wiring diagrams to see if the cigarette lighter socket shares any wiring with the glove box lamp or any other wires in the area of the glove box.

Cheers,

Don

 

Thanks for the reply Don. I was actually referring to the cigarette lighter that's located just ahead of the transmission floor shifter. When the original blower module failed (again) last December, I borrowed my sister's small electric defroster which plugs into a cigarette lighter. When I plugged that unit into the cigarette lighter socket, there was no power. Apparently, the former owner had problems with it too as I found a blown 20A fuse in the trunk fuse box that was used in place of the recommended 15A fuse.

Well, after replacing the 20A fuse (I didn't have a 15A fuse lying around at the time), the small electric defroster worked fine for the first 12 minutes, and then the fuse blew again. I subsequently replaced that 20A fuse with a 15A fuse.

I don't have the wiring diagram before me, but I'm assuming that the 15A fuse only powers the cigarette lighter so I suspect that the cigarette lighter socket is likely shot.