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Aircon clutch fuse blown

nlcrane
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Re: Aircon clutch fuse blown

Postby nlcrane » Tue Jul 02, 2019 9:52 am

Both relays are pin compatible and can be inadvertently interchanged. The dark blue relay (Hella 4RA 003 510-34), however, has our old friend the quench diode internally mounted across the relay coil terminals, this is to quench the reverse emf caused by the collapsing magnetic field on de-energizing and to prevent this reverse current from damaging any downstream components. The light blue relay (Hella 4RA 003 510-68) has no diode, but has a current limiting resistor mounted in place of it.
My guess is that the diode had shorted, so the relay could not energise and so the clutch couldn’t be pulled in.
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1994 Sovereign Gold 4.0

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rvdz
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Re: Aircon clutch fuse blown

Postby rvdz » Tue Jul 02, 2019 10:14 am

nlcrane wrote:Both relays are pin compatible and can be inadvertently interchanged. The dark blue relay (Hella 4RA 003 510-34), however, has our old friend the quench diode internally mounted across the relay coil terminals, this is to quench the reverse emf caused by the collapsing magnetic field on de-energizing and to prevent this reverse current from damaging any downstream components. The light blue relay (Hella 4RA 003 510-68) has no diode, but has a current limiting resistor mounted in place of it.
My guess is that the diode had shorted, so the relay could not energise and so the clutch couldn’t be pulled in.


I think you're right. The relays have a little diagram printed on the side. The dark blue one does indeed have a diode between two pins in the diagram, which isn't there on the light blue relay.
Very interesting stuff, I've definitely learned something new. So if the dark blue relay functioned properly, I would have never had an issue? According to the Haynes manual it should have been a light blue relay, but wouldn't the dark blue one be safer?
Roel

1994 Sovereign 4.0 Auto [698760]

nlcrane
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Re: Aircon clutch fuse blown

Postby nlcrane » Tue Jul 02, 2019 11:00 am

You need the dark blue relay and not the light blue one. The photo shows my MY 94 set-up, dark blue relay, green base. For some reason the documentation, Jaguar and Haynes, gives the colour as being light blue. Could other owners open their bonnets and confirm this, it is not the first time that the schematics have been wrong.

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abercanadian
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Re: Aircon clutch fuse blown

Postby abercanadian » Tue Jul 02, 2019 5:33 pm

Sorry can't check the colours because I don't have the original relays any longer. :shock:

After going through some electrical issues a few years ago, I found that the Hella light blue relays were the subject of a Jaguar bulletin so I replaced them with the recommended black sealed relays.

The bulletin posted below will also clarify the use of the various relays.

https://www.jaguarforums.com/forum/attachments/xjs-x27-32/5753d1287420981-t-s-b-s-86-178a-inoperative-blue-relay.pdf

Larry
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94 XJ40 VDP vin 701729
Oyster Metallic/Doeskin on Aero Alloys
230,000 Kilometers 143,000 Miles
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94 XJ40 SOVEREIGN vin 703632
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nlcrane
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Re: Aircon clutch fuse blown

Postby nlcrane » Tue Jul 02, 2019 6:25 pm

abercanadian wrote:Sorry can't check the colours because I don't have the original relays any longer. :shock:

After going through some electrical issues a few years ago, I found that the Hella light blue relays were the subject of a Jaguar bulletin so I replaced them with the recommended black sealed relays.

The bulletin posted below will also clarify the use of the various relays.

https://www.jaguarforums.com/forum/attachments/xjs-x27-32/5753d1287420981-t-s-b-s-86-178a-inoperative-blue-relay.pdf

Larry


Excellent piece of information Larry, many thanks for sharing. The old pull out and push in again is sometimes all these old ladies really need.
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rvdz
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Re: Aircon clutch fuse blown

Postby rvdz » Sat Aug 17, 2019 8:15 pm

Still having trouble with the aircon. I noticed the air wasnt being cooled again. So checked the fuse, checked the relay and everything seems fine. When I take the relay out and just connect the terminals I can hear the compressor starts to run.

Now I'm not super confident in the garage that did the re-gas, I suspect they didn't check the system, just topped up the gas without checking for leaks etc.

So would my assumption that all the gas has escaped and the compressor doesn't come on because the pressure is too low be correct, or is there something else I can check?
Roel

1994 Sovereign 4.0 Auto [698760]

pimgmx
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Re: Aircon clutch fuse blown

Postby pimgmx » Sat Aug 17, 2019 8:22 pm

Another known weak link in the A/C chain of late model years is the so-called trinary switch, replacing that solved the A/C issues on my early '94 Sovereign and late '93 Insignia...

I'd suggest to check for leaks for first, though, before you start replacing parts that might still be OK!

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naki_k
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Re: Aircon clutch fuse blown

Postby naki_k » Sun Aug 18, 2019 12:23 am

pimgmx wrote:Another known weak link in the A/C chain of late model years is the so-called trinary switch, replacing that solved the A/C issues on my early '94 Sovereign and late '93 Insignia...

I'd suggest to check for leaks for first, though, before you start replacing parts that might still be OK!


Ditto.
Try another garage though maybe.
You do need to ascertain that you still have adequate gas in there first. Otherwise you are chasing your tail.
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90 Range Rover Vogue SE 3.9 V8 LPG
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93 6.0 XJ81 DD6 x2
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abercanadian
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Re: Aircon clutch fuse blown

Postby abercanadian » Sun Aug 18, 2019 2:27 am

A good way to check for a leak is to pick up a UV LED flashlight - (there are some really good ones on eBay for not too much money)

Try to take the car into as close to total darkness as you can and start shining the light into the engine compartment. Shine it along the a/c hoses, ports, unions, compressor and through the grille to the condenser. If you have a leak you should see the leak point glowing brightly from the trail of dye that has escaped from the system.

Good luck,

Larry
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94 XJ40 VDP vin 701729
Oyster Metallic/Doeskin on Aero Alloys
230,000 Kilometers 143,000 Miles
Daily Driver

94 XJ40 SOVEREIGN vin 703632
Diamond Blue Metallic/Barley
111,000 Kilometers/69,000 Miles
Parts Car

naki_k
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Re: Aircon clutch fuse blown

Postby naki_k » Mon Aug 19, 2019 9:39 am

abercanadian wrote:A good way to check for a leak is to pick up a UV LED flashlight - (there are some really good ones on eBay for not too much money)

Try to take the car into as close to total darkness as you can and start shining the light into the engine compartment. Shine it along the a/c hoses, ports, unions, compressor and through the grille to the condenser. If you have a leak you should see the leak point glowing brightly from the trail of dye that has escaped from the system.

Good luck,

Larry

Assuming it’s not just blown out of the pressure relief valve like mine (covering a good part of the engine bay).
Last edited by naki_k on Mon Aug 19, 2019 3:22 pm, edited 1 time in total.
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300