Title says it all...On my base S-Type, the A/C went on me and I assumed it was a DCCV...

There are multiple common failures. The actual valve (DCCV) is only one, but commonly then takes out the module - either a burnt PCB trace or a driver transistor. An inline fuse would stop the trace but maybe not the transistor, though it might (normally a crazy idea but the failure mode appears to be rising current rather than an immediate short). You'd need a fuse for each side of the DCCV, of course.

What amp fuse would you recommend?

Beats me! I think the valve takes over 1A (per side) to stay closed (you might measure it LOL), but what it takes peak when cold? Don't know. And what would blow in time to protect the PCB trace? Maybe 2A? Slow-blow type?

Even 1.5A fuse might be enough. But maybe 2A draw is "normal" - again, maybe try measuring it?

Caution: I'm not an electrical circuit designer! (I get by, is all.)

You should be able to put the fuse anywhere you can get at in the wiring between module & DCCV, so maybe could find somewhere fairly convenient and experiment, starting with a lowish value and if it keeps blowing then bump it up a bit. Horrors. Am I really saying this about a jag????

The solution is already out there. An aftermarket company that rebuilds the Jaguar climate control modules can for an extra fee modify the climate control module so it's protected from too much current when the DCCV goes bad. This really should have been designed in from the beginning and it's a rather small modification.

If you have not read this site you should. They not only repair the modules, they post a set of great instructions so even a DIY guy can fix it himself if desired!!

- JaguarClimateControl.com
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They don't tell you what or show you how to fit protective circuitry, do they? (I couldn't find it.) They'll fit it for $(quite a lot).

I guess not the exact wires? But our own forums have the repair here;

DIY Climate Control fix for jaguar s-type 2003+ FAQ - Jaguar Forums - Jaguar Enthusiasts Forum

I also found the beef up instructions for the module but can't find them right now.
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But Bacardi asked what fuse to use, which that thread also does not say as far as I can see.

I recently took my 03 in for AC repair as the air was always blowing on the windshield no matter what setting. The repair facility mailed the climate controller to TX or AZ, I forget. Whoever rebuilt it did an amazing job. It's the coldest AC I've ever had in a car. Even on the lowest setting it's too cold and I'm very warm-blooded.

I thanked you but that's just how to fix it after it's broken...

The guys at JaguarClimateControl.com have told me that there's not much you can do to protect your factory DCCV, and sooner or later they will all fail. They say to keep it clean and dry (i.e. no engine bay washing and keep your belly pan on the car), keep your coolant clean and topped up properly, and that's about all you can do. Even while taking these precautions, they say that all DCCVs will eventually fail. I do a white-napkin-wipe on ours every weekend, and thus far it has always come back clean. If and when I see coolant stains on the napkin, I'll know it's time to change the DCCV....

Here's another tidbit that the guys at JaguarClimateControl.com mentioned to me. They do quite a number of repairs on S-Types that initially suffered from the infamous plastic nipple coolant leakage on the coolant expansion tank. If the owner does not catch this leak soon enough, the leaking coolant tends to drip downwards, coat the DCCV, eventually seep into its electrical connections, and then BAM! It shorts out and takes the CCM with it....

So when you do your napkin-wipe test on your DCCV every weekend while you're checking your oil and tire pressures, be sure to take a quick look at that plastic nipple connection as well....

Don't you just love this S-Type Precautionary Maintenance Checklist of problems you should be routinely watching out for? Before much longer, it will run a full two pages....