87 XJ6 Delanair MKII, No fans

Finally got some time to work through the HVAC on this car and I am stumped.
if I disconnect the solid colors from the AC relay and apply 12v, the fans run no problem.
The mode selector appears to work as all the air moves around where it is supposed to.
I probed the round connector and all the values match what are indicated in the schematic included with the delanair zip file.
I bypass the coolant temp sensor.
I pulled the AC relays and tested each relay and they are all working as they should.
I suspect I am missing something obvious.
Where is the in-car temp sensor located? When you google you get 90 dif answers.
Any help is appreciated, thanks!

I see that you are new to Jag-Lovers. Welcome!
Forget using Google. Jag-Lovers has a superb archive of every post back for decades. At this point pretty much everything about these cars has been discussed endlessly and all that history is available to you to search at your convenience.
Just search the Jag-Lovers XJ archives for “A/C amplifier” and you will find hundreds of posts from those who have had problems with their Delanair MK II climate control system and what they did to resolve the issue. Some of those posts will be from me as I struggled to keep the climate control systems in my two Series III XJ6s functioning properly.
By far the most common failure mode is a failure of the A/C amplifier. I had several of them fail on me over the past 22 years including ones that worked perfectly until they failed, ones in parts cars that I purchased that were already bad, and used ones that I purchased on eBay that were bad when I got them. There are some aftermarket alternatives including ones from Jag-Air. All of this is detailed in the archives.
The in cabin sensor is located beneath the crash roll. You will need to remove the crash roll to find it, but the sensors rarely fail. If your system is not working properly and/or its operation is random or flaky you have a bad A/C amplifier. The only way you can resolve this is with a functioning A/C amplifier.


Ah ok, that was my other question.
I was under the impression that if the AC amp failed it would still blow but none of the flow control etc would operate.

I’ll have to get an AC amp then, though $600…ugh heh

Not sure where you are based Brian?
Direct from Jagaire only US$329?

Think I need one too, but here in NZ probably will be NZ$600 :frowning:
Cheers Dave

I am in Canada, so $329USD almost doubles by the time it gets up here with dollar conversion, shipping, and duties.
But…I see they have a manual control for $149usd. hmm

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The A/C amplifier is indeed the most common failure of the system, but it’s sole purpose is to move the servo and has very little to do with the fans, exept of the microswitches at the servo that control the fan speed when in Auto mode.
The in-car temp sensor has also no input on the fans.
So, the fans are basicaly controled by the fan speed selector, the servo microswitches, tha main relay and the resistors pack.
When the fan speed selector is at Low, Max or Defrost the servo microswitches are bypassed.

If I understand correctly, you say the when you move the Mode selector the servo works and moves all flaps at the correct positions. If this is the case, it would indicate that your AC amp is doing something.

First of all check the most obvious,i.e. the fuses.
You bypassed the coolant temp sensor, so it’s not the problem, but leave the bypass until you figure things out.
Check if the main relay has power and if the speed selector is giving the right signals.
Next is the resistors and report back.

The ‘Lo’, ‘Hi’ and ‘Def’ works independently of the AC amp, Brian - the AC only controls the servo. In ‘Auto’ the fans are controlled by the servo, but the servo is then either at low or high fan speeds - the AC amp may give wrong speed, but not ‘no speed’.

At the relay bank; the brown/white wire delivers power from the 50A fuse (#3 or #16) to all relays internally. Microswitches, on the function control and servo, then controls which relay is ‘switched on’ - and power from the ‘on’ relay is then passed through a resistor unit, varying fan speeds.

Check for power on brown/white with ign ‘on’ - if no power; check fuse and fuse holder. Jumpwiring 12V directly to brown/white bypasses the fuse - if fans works OK, at different speeds, with power on yellow, red, blue and green/slate; the resistor unit is OK - and a ‘no fan’ situations implies no power to the relay bank.

Or something exotic - if the suggested test gives no result. Like wrong connections on the relay bank; if the brown/white is not connected to the correct terminal - there is no general fan power to all relays - and if connections are all messed up…who knows…:slight_smile:

The in-car sensor sends its resistance to the AC amp, which signals the servo to turn in the appropriate direction. A ‘break’ (high resistance; cabin cold) turns the servo to full heat - a short (no resistance; cabin hot) turns the servo to full cold. In both cases; the fans should run at high speed…

As a aside; a not infrequent problem is the fuse holder dislodges fuse connections due to high current load…

xj6 85 Sov Europe (UK/NZ)

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Frank, Thanks for the info.
Will delve more into it after work.
I had jumped from the brown/white to the fan wires and got fan action.
I pulled the relay pack out to test them and will put it back in today and verify the wiring order to the relays.
Just need to accidentally print out the schematics in color at work :slight_smile:

With fan action on every fan wire at the relay it indicates that there is power on brown/white, Brian.

In principle, as the fan wires go via the resistor unit, you should get 4 different fan speeds with the jump but does, of course, verify relay pack function and connections. With the wiring diagram, you can at least verify correct connections and test relay bank functions. That all 4 relays should fail, and give no fans at all, is beyond belief… :slight_smile:

Check that the disconnected black/blue is plain ground with the function switch out of ‘off’ - without that ground at the relevant microswitch, the relays will not operate…

xj6 85 Sov Europe (UK/NZ)

Turns out it was the green wire coming from #6 fuse.
Somewhere there is a break.
S57 seems to indicate there is a junction somewhere but I can’t locate it.
Ran a new wire and bingo, everything works properly!

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Any sign of burning/distortion at the fuse box, Brian - a not uncommon problem? Anyway, as long as the new wire is fuzed through #6, all is well - well done…

xj6 85 Sov Europe (UK/NZ)

Pulled the fuse box, all looks good.
Which is amazing considering this car had a plugged sunroof drain and 4" of water in the footwell when I got it. Everything works!
Soldered onto the wire after it leaves the fuse box.

All good now!