The other day we were doing our normal Hit Run/Foraging Mission when, late in the afternoon, at 90+ degrees F, totally without warning, the blowers quit.

Oh Goodie! Now what? I Just replaced the perishable parts of the system a mere 4 years ago, winter 2018-19; "new" (rebuilt) servo, "new" (good quality used) mode control, New Amp, New clutch relay. And it all worked Just Fine until suddenly it didn't.

A BLACK car on a warm June afternoon with no AC is NOT a pleasant experience! It was a very warm and Tense drive back out here.

I dropped the fuse cover and this is what I found:

That right there is a 50 Amp flash tube, aka Blower fuse! Said right on it Lucas 50 until it got burned off.


It wasn't the main element that failed, it seems to have come loose from one end. Didn't do any good for the fuse holder either. Little blobs of plastic tried to drip out.

When we bought the car the PO sternly warned me to "Put it on AUTO and leave it there!" And I did, until about a week ago, when it occurred to me, I've changed out that MODE switch! I can put it anywhere I want to now. So I started fooling with fan speeds. And, discovered there is no LOW fan! LOW position gives HIGH fan speed. So, there's something wrong after the switch, doubtless causing overloading of the circus and blowing fuses (this isn't the first time it's blown. The extra in the fuse cover is already gone)

OK, so now to find a replacement. HA!! Fat Chance at any local parts house. 35A is their biggest.
I bet Google knows where I can find one. But I need one NOW not in a week or 10 days.

AHA! There's the Red S3 Junker out back! Maybe I can cannibalize a fuse from that.
YUP! Had a paper label inside the glass! Sez "LUCAS-20A constant load, 50A surge."
EDIT: So I could have put in a 35A fuse and been OK. Wish I'd known that before I spent 2 days stressing. /EDIT

All good now. I have a tin of 5 replacements on the way for if this happens again.
(';')

 

I bet the mode switch is not the culprit here. The fan speed are contrived by the "Main Relay" and the fan resistors. Both behind the panel in the driver footwell covering the center console. The main relay is actually 4 relays in one box that selects resistance elements in the fan resistor. The fan resistor is three open wire resistance elements that are selected in parallel and series to slow the fan down. If it is on high, then none are selected and full 12V is applied to the fan. The relays are conventional mechanical relays the can suffer dirty and corroded contacts and occasionally a broken coil wire, both conditions that are correctable with careful disassembly of the box.
All this in in the S57 Electrical manual, also in the Delanair manual I'll attempt to attach.
Good luck.
A hot car is not pleasant.
Niles

 

AHA!! I didn't think the Mode Switch was the problem, as it was a Pre-existing issue when I got the car.
The Relay, on the other hand, is the only Climate Control part in the 'dog house' that I didn't change!
Right there's a project for next winter!

Doncha just Love the 'Job Security' of owning a Jag?
It kind of makes our otherwise miserable existence worth while, doesn't it.

 

Yup. And a project it is. There are a lot of wires jammed in that area. It's difficult to disconnect it (not a connector block, just individual spade connectors) and pull it out. The resistor is not much easier. But if the problem is High speed only, the resistor is being bypassed. I'd figure a relay that is not pulling a resistor into the circuit.
Niles

 

Actually, on Auto I do have 3 speeds at least, so the relay is working at least some of the time.

I'll look into it more closely next winter. But thank you for giving me a starting point.
(';')