Ignition load relay on Disco 1 300 Tdi

[Thys]

This reply from disco-al got me thinking:".....check the ignition load relay. had problems with my a/c not working (it had been bodged with a 12v feed from the fusebox), turned out the ign load relay was faulty and not allowing the a/c any power. it's in the rh footwell behind the kick panel, water had been getting in through the "ventilation holes" in the A panel "

I have the clattering relay and the AC compressor intermittantly starting.

Refrigerant charge is good, and clutch clearance good.

With the AC switch on, the condensor fans run, and the orange indicator light is on.

I replaced the compressor relay, the yellow one on top of the three relays in the RH footwell.

The new one also clatters.

The combined pressure switch, when the AC button is on, has no open circuit, voltage reading over the two wires is 0 Volt.

In the LH footwell I found a rather hot yellow relay, switching when I switch the AC on. I replaced it, no change.

I traced the wires, and found a multi plug with two thick wires and one thin wire plugged into a unit between the evaporator and fan. Cannot get the plug out, thought this may be the problem.

This ignition load relay has me thinking. My Disco has the habit, and this has happened three times now, while driving all electric power goes, like in a millisecond, and then comes back on again, twice at night and last time during the day, the two night ones was easy to observe, a quick flick of darkness, and the clock resetting to 0:00, The last one was during day time, and I noticed the clock had reset again.

Which one of the relays in the RH footwell is the load relay, maybe that is my Disco's problem?

[teabag]

Ignition load relay? never heard of that one nether is it listed in my books.

There's an a aux or accessory relay listed and that is ignition switch controled, I believe it is yellow or has yellow connections YWB10027L so a standard relay.

There a few relays involved with the operation of A/C which seem to be yellow also, also a relay can 'chatter' if it's picking it's earth via another relay so have a look at the earth connections in the footwell.

[Thys]

Thanks Teabag, will check the individual earth connections.

[john242]

ignition load relay K127 located rh footwell behind the kick panel trim and its nearest the bulkhead,according to the rave disc that i have,could be wrong,but may be worth a shot

[Thys]

Thanks john242, I fount the ignition load relay, if i pull mit out the condensor fdanns stop, I then found a second relay in the LH void below the cubby hole, and if I pull than one out, the condensor fans stop and the orange back light on the AC switch goes off as well. The 3 rd relay, in the RH foot well , on its own, above the row containing the ignition load relay is the one that clatters, or does not energize at all. When that one energizes, the compressor clutch engages.

I will now trace the wiring back from that compressor relay to try and determine the fault. The cluster of relays in the RH foot well has a multi connector for the earth wires (black) and that is bolted to the body. All those are secure.

The combo pressure switch's two wires shows 0 V when the system is on, thus down stream the power supply is interrupted.

[john242]

the relay above is the a/c clutch relay,if heater blower is in position 1,2,3,or4 an earth is provided to pin 86 of the relay via the dual pressure switch contacts.the earth circuit can also be interupted by the evaporator temp sensor in the (heater) box if it senses too cold ie ice.hope this helps.

[dave88sw]

the clock is on a permanent live feed to keep the time so surely if thats resetting your fault is more likely to be the main positive feed from the battery or a main earth lead.

[Thys]

Thanks john242 and dave88sw, what drives me up the wall is that late yesterday afternoon all started working perfectly fine, my worst enemy in fault tracing is an intermittant fault, I will have to re-check all the connections from the earth connector on the compressor relay through the combo press switch and the evaporator temperatrure switch.

The main earth circuit and power supply to the clock circuit will follow.

[Thys]

the relay above is the a/c clutch relay,if heater blower is in position 1,2,3,or4 an earth is provided to pin 86 of the relay via the dual pressure switch contacts.the earth circuit can also be interupted by the evaporator temp sensor in the (heater) box if it senses too cold ie ice.hope this helps.

I stripped out the glove box, the AC front panel, radio. I proceeded to trace wire by wire. Eventually I found the open /intermittent circuit between the evaporator temperature switch, unit no 65, and pin no 86 on the compressor clutch relay, unit no 58.

Now, betrween these two units a compressor cut out switch is shown, unit no 63. Now this seems to be the culprit, if I only knew where it is, I cannot find it.

The wild fix would to simply bypass the unit's circuit by linking the temperature switch directly to pin 86 on the compressor clutch relay, but that compressor cut out switch is there for a reason.

Any body seen this comp cut out switch? My Disco does not have the rear air con, neither the electroninc diesel system.

[Thys]

Well, goging against my training and better judgement, I linked the terminal of the evaporator temperature switch directly to pin 86 of the compressor clutch relay, but keeping the wire intact on the harness at pin 86.

All works good. The temperature switch cycles the compressor clutch, and if I disconnect the combination pressure switch, the compressor cloutch releases, thus the main protection function of the refrigeration circuit functions, and the temperature control functions.

I am going to give it a go and see what happens.