Outer Limits 4x4 Board

intermitent air con clutch

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In the last week or so the aircon compressor in my 1990 range rover seems to be playing up.the magnetic clutch continually engages and diengages making a clicking noise. It does it all the time.. It doesn't seem to effect the working of the aircon as it still cools OK.

Has anyone else had this happen or has anyone got any ideas why it is happening and how I can fix it.

I have done the following tests

i have gas in system

bypassed/shorted hp and lp

also bypassed condesor fans

and swapped over some relays(namely clutch relay)

i have also done some metering,and found that when i disconnect the compressor/clutch i have between 12.45-13v at the plug and also at the relay feed out to the clutch.

what i have noticted though after 10 beers last night and more than that tonight is

the inputs to the relay do not drop out (bypassed/shorted)guessing they are the hp/lp maybe

when i hook the clutch/compressor plug back up and check voltage from the plug output ,it drops to around 11.75-11.85v(remains at 12.45-13 at relay output).and when it cuts out ,well ofcourse nothing,is there some sort of resistor in the clutch to regulate the power causing this.

all help appreciated ,thanks again

shane

also i have run direct power from battery to the clutch and it doesnt drop out

When you say you have gas, have you had an Aircon guy evacuate and recharge?

One thought I had is that the LP is activating. I know you bypassed the switches but maybe it activates then deactivates. have you checked the LP while the clutch does not work.

AFAIK, the clutch is just a solonoid which pulls in . The voltage drop is probably normal, but you could try a new circuit with a relay activated by the other relay.LOL

Regards Philip A

forget wrote:and when it cuts out ,well ofcourse nothing,is there some sort of resistor in the clutch to regulate the power causing this.

I am not sure if I'm reading this right, but if you're saying that when the clutch cuts out there is zero voltage at its plug, then you need to look at the relay/electrical/pressure/gas side of things, because it means the system is actually turning the clutch off "on purpose".

On the other hand if you're saying that the clutch is cutting out even though there is still ~11.8 volts at the plug, then you have a different kind of issue which might be fixable by cleaning up the wiring (to get less voltage drop), replacing the clutch, or possibly dismantling it to reduce the gap so the magnets aren't working as hard.

I am not sure if I'm reading this right, but if you're saying that when the clutch cuts out there is zero voltage at its plug, then you need to look at the relay/electrical/pressure/gas side of things, because it means the system is actually turning the clutch off "on purpose".

Well yes I am asking have you checked the voltage at the clutch when it is stopped vs when it is going? If no voltage there then suspect the LP switch/relay and maybe the gas charge, as it may be turning off deliberately.

I have heard on one of these forums of a problem where the clutch will not pull in when the thermostat tells it to , because of the clearance becoming larger and the solonoid being too weak.
Perhaps you should have a multimeter across the wires and see if that is the problem, as there will be no voltage until the thermostat cuts in, then the voltage will be applied. If the clutch engages as the voltage is applied then the clutch should be OK but may not be if starting is inconsistent.
I was joking a bit re an extra relay as you would be driving a relay with a relay, but if the clutch works with a direct battery feed then you may have a loom connector resistance problem. Or maybe even an earth problem. In this case maybe a simple fix is a new circuit , as you can drive yourself mad finding these things sometimes.

Another possible problem is simply the thermostat is playing up and has lost its hysterisis . ( been itching to use that word) , ie the temp difference between off and on has narrowed. Listen for the clicks with your head near the Aircon unit or find the wires and check whether the voltage is rapidly going on and off, or check the relay signal wire.
I think the secret is to do these things dynamically, ie check while its running.

Regards Philip A




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Philip A wrote:I have heard on one of these forums of a problem where the clutch will not pull in when the thermostat tells it to , because of the clearance becoming larger and the solonoid being too weak.

This is common with the P38s and a lot of us have had to remove a shim from inside the clutch set-up to reduce the clearance.

With mine, I've had to go a step further and sand one part back a bit as well so it all sits closer together.

The magnet weakening over time is a common problem with a lot of compressors. You only need the tiniest amount of clearance (it's either touching or it's not) for the clutch to do its job properly.

I was joking a bit re an extra relay as you would be driving a relay with a relay, but if the clutch works with a direct battery feed then you may have a loom connector resistance problem. Or maybe even an earth problem. In this case maybe a simple fix is a new circuit , as you can drive yourself mad finding these things sometimes.

Believe it or not on the P38 there was a recall because of the issue above. The fix is a relay closer to the compressor. But, because the BCM is too smart for its own good, it needs to sense the load of the compressor clutch or it records a fault and turns off the circuit. So, there is a separate loom including a relay and a great big resistor to simulate the load. It is such a stupid pile of crap but it is the official landrover fix - even though you would think that they were joking too. I prefer the reduced clearance mod that just works with the lower voltage instead.

But... none of this would apply to a 1990 model afaik.

thanks philip,i was looking at the clutch and found no problem .



i ended up pulling the dash out and found that where the slider is for the hot and cold ,it goes to a cable which must operate the vents,but what i found was that also the thermometer switch also conncts to the slider,which unfortunatly had become dislodged and left the thermostat on the heat control,hence there was my problem.



bloody shit of a thing!