Air Conditioner will not switch off

[Conradk]

I've searched the forum without success to see if anyone else has experienced the same problem. My '99 4.5L has the automatic air conditioning unit fitted and the control appears to be working perfectly (temperature contol, fan settings, auto/maual, etc all working fine). However, in recent times I've noticed that even when you switch the aircon off the compressor and fans continue to run. Only after I've switched the ignition off did they shut down and then stay off after I restarted.

More recently, Ive noticed that about 30 seconds after starting that both the compressor and the fans kicked in (2 different relays) and then run continously despite the fact that the control unit is switched off. As of yesterday, the moment I switch the ignition on the cooling fans now come on and I assume the relay for the compressor probably also energises. In desperation I've pulled both relays for the moment until I find the problem.

At the moment I'm working on the assumption that the automatic control box is not the problem because all indications are that it functions correctly, and that the problem may be a second relay or switching device that takes instruction from the control unit to switch the two relays in question. Can anyone help me on where to look (I cannot see anything obvious on the wiring diagram).

[NP99]

Could it be a faulty dash switch??

[happygu]

I too would second that the dash unit has a faulty switch.

Pull it out, and give it a good clean and check all the contacts.

Mic

[Yendor]

I would try swapping the A/C relay with a known good relay first.

Were any accessaries fitted to the vehicle around the same time this problem started? any extra cooling fans fitted?

[NP99]

This might help too -
http://www.nissanpatrol.com.au/forums/showthread.php?12476-Air-Con-only-quot-ON-quot

[Conradk]

Hey NP99, if the saga of the sub tank reset is anything to go by the disconnect de-energise and reconnect trick may just do the trick. I will try this as soon as I can get under the bonnet and if it works I will declare you a genius for finding the thread and Yendor a genius for yet another good solution.

[Conradk]

Just to close off this thread, after my last post I still battled for another month to try and solve this problem but without any luck. Mean time, I now also noticed that the plastic covers over my spots were distorted only to find that the spots were staying on permanently when the ignition was switched on - melted plastic. At this point I now had pulled three relays out to shut down the problem and in desperation phoned up the local auto electrician I had used three months earlier to tidy up the wiring around the relay box............... I suddenly smelt a rat!!! And Yendor's comment two post up about any accessories having recently been fitted struck a cord! The problems could have been present from the moment I got the van back after the wiring tidy-up but did not immediatly notice it because March/April was hot as hell and the airconditioning was on full time. And because the spots have got covers I would not have seen them on.

So I took the wagon back to the same auto electrician to see how quickly he could sort all the problems. "Surprisingly" he solved the problems and fixed all the wiring in less in two hours and charged me very little. Yet no matter how much I pressed him for a detailed explanation of what the problem had been he remained vague and simply said he had found "some bad wiring that someone had previously done" and then proceeded to change the subject.

It does not take a rocket scientist to figure out that he had stuffed up in the first place, but was simply not man enough to admit it. One positive about this though is that my faith in the Patrol's reliability has been renewed. Once again, it was not a 'trol problem but rather someone's finger problem.

[Yendor]

Thanks for the update.

Glad to hear you got it sorted.

Generally speaking Nissan's electrical engineers did a good job on the Patrols. Not much goes wrong with them electrically that wasn't caused by owner abuse, accessaries being fitted or mods done.