See video below, but here’s the deal:

Turning blowers on doesn’t do anything, but the blower control module is getting 12.5 V and I can turn the blowers on by manually pressing any of the “triggers” (except for one, but the low and hi ones work and that’s good enough for me).

Not an electric expert so wondering what I should test next and how. Much appreciated as always.


Anderson

 

What you've got there is the relay pack. It is 4 relays incorporated into a single housing. And you're exactly right: each relay has a coil which, when energized, pulls contacts together to complete a circuit.

It is normal for each of the relays to have constant 12volts on one of the posts.

The relays are triggered/energized by the servo. The servo is an electro/mechanical device with numerous switches and valves, including the blower control switches.

First thing to do is check the four system fuses. Or, in your case three...as we now at least one of them is OK because you have that constant 12volts. Two of the four are in the fusebox(es). Another is behind the console RH cheek panel on brown/yellow wires. The last is on the ground wire at the amplifier, behind the console LH cheek panel

If the fuses are good then there's another easy step: Turn the temp control dial and listen for a whir. The whir doesn't prove that the servo is operating correctly in all respects. It just proves that it isn't outright dead. No whir means deeper checking

Last on the list of easy steps is the blower motor thermo switch. It is on the heater core pipe, not easy to reach; some digging. Remove the two wires and jump them together. Do the blowers now operate? (An alternative digging is to remove the LH cheek panel at the front of the console where you'll hopefully find two dangling grey wires. These are test wires which can be jumped together for the specific purpose of bypassing the thermal switch)

Cheers
DD

 

Thanks for the detailed response Doug. A few questions before I dive in this evening:

1) “Cheek panel” - are you referring to the panel that is removed to access the main fuse boxes or the smaller panels adjacent to the driver’s leg which houses the small floor vent (like the ones I took off to access the relay pack)?

2) What does the amplifier look like?

3) The two fuse box fuses you mention, which are they? I think #10 is one and #5 is the other but the wiring diagram I’m looking at online is for 1989 and mine is an 83 (I can’t find the diagram in my green book).

Thanks

 

The one with the vent. Remove the vent screws, wriggle the panel forward and away

Originals looked like this but many have been replaced by one that looks like a shotgun shell




Probably number 10 and 11 in the LH fuse box...but I can swear to it

Bear in mind that you're not looking only for blown fuses but also looking for corroded contacts

The fuse boxes are behind little access doors in the LH and RH under-dash trim panels or "knee panels"

Cheers
DD

 

Thanks Doug. Are these the two grey wires you mentioned that I could jump to bypass the thermal switch? They’re hanging by the left cheek panel but the wires themselves are brown, not grey.

 

I replaced the fuse by the amplifier behind the rh cheek panel.

Can confirm the servo comes on when I put the switch in low mode.

Do you have a wiring diagram of the old school relay box? I can’t find one in my book and the one I found online is for 1989.

Here’s really the issue: the relay box is getting 12.5V, but the wires that charge the individual copper coils to complete the circuit do not get voltage when I turn the switch. I can’t see where all the relay box wires go to know where the fault might be which is why I’d love to see an older diagram.

The only oddity I’ll add is that the #10 fuse for the AC motors has been re-wired though I’m still not sure how. I’d have to take another video to show what’s going on there. But - if the blower relay box is getting a constant 12V would it matter how fuse #10 is wired?

 

Those are the ones. Sorry about the color mx-up. i was obviously remembering the connectors, not the wires

Cheers
DD

 

PM me your email address and I send an older diagram to you

I don't think so...but you never really know about these wiring changes.

Cheers
DD

 

Here’s the latest:

Resoldered some of the coil “post” wires in the relay pack. Nothing seemed to be different.

However I did notice the defrost fans work, though I don’t think I ever tried those to begin with. Not sure what this indicates.

Then I jumped the two brown wires behind the LH cheek panel and I was able to turn the fans on in auto and high modes, but not low mode.

So I guess the temp sensor on the top heater core house is malfunctioning; if this is a safe assumption can I also assume that replacing it will resolve the no low fan issue?

 

The fan speed on the Delanair II is also affected by the resistor module. This is a thing with curling wires strung across a bridge and according to the fan speed selected, one or other of the wires provides a suitable resistance to alter the current to the fan motors and thus moderate their speed.
If the low speed resistance wire is fractured on this gizmo, the low speed may not work. The Great Palm's book goes into detail about this and how to fix it.
It is shown as item 3 in the diagram attached to post no. 14 on this thread by Doug:
https://www.jaguarforums.com/forum/x...basics-178058/

 

I have a similar prob or maybe no prob at all. I turn on the demist and have to slap the 'cleaned' relay to get it on, turn it on any other speed nothing untill the engine starts to warm up about 2 minutes. Then they all come on on demand. I am following this post with interest.

 

What relay are you referring to?

 

Thanks Greg, I’m going to make sure aux fuse #5 is getting voltage and if that doesn’t affect anything then I’ll be looking at the passenger side resistor since that one should be easier to access.

Question: are the temp sensor bypass wires specifically for testing purposes or can I jump those permanently instead of replacing the sensor?

 

There is only one resistor, and I have no idea if you can get at it or not. Sorry I cannot help with the bypass question.

 

Sorry was thinking of the transistors spoken of here: https://forums.jag-lovers.com/t/xj-s...r-relay/344041

 

Doug where can I locate the resistor?

And same question I asked Greg: can I permanently jump the two bypass wires or do I need to replace the temp sensor on the heater core pipe?

 

Jump them permanently if you prefer

That sensor serves but one purpose: when heating is called for it prevents the blowers from operating until the coolant is hot enough to actually provide heat.

Cheers
DD

 

Got it, thanks.

Good news: the low fans now work when I jump the sensor wires.

I must’ve misread or overlooked your initial comment amount the in-line fuse behind the LH cheek panel. Fuse was okay but the connection might’ve been poor. Cleaned it up and reinstalled. That’s the only thing that I’ve done this morning.

Thanks as always for the help Doug. I owe you one, or five or ten or something.

 

The transistors apply to the Delanair Mk III system. You have the Mk II system. The electricals are very different between the two

Cheers
DD

 

LH side of the main heater/ac case, a few inches above where the amplifier is located

Cheers
DD