Air con compressor kicks out on tickover

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nigelc116
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Joined: 22 Oct 2005, 17:47

Post by nigelc116 » 21 Jul 2006, 17:29

Well the alternator is swapped I've got 14.2 Volts at the battery but the air con compressor is still not still working at tick over.

The fans both spin at tick over but the compressor does not as I rev the engine the compressor spins, as the revs drop back to 1000 the compressor stops.

I've found a relay in the engine compartment behind the battery that clicks on and off with the comperessor, but I don't know what feeds this. There is continuety between this relay and the pressure switch on the condensor.

Has anyone got ant ideas please

sub42
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Post by sub42 » 21 Jul 2006, 18:22

Hiya,

You might want to take a look at you HP and LP switches. I would say that its going out on low pressure. Once pressure is created by revving the engine it comes to life, once the rpm, and pressure drops, off it goes. I dont know what state they switches on your system are, but would guess at status good=closed, staus low=open circuit. Thats for the LP side. All guess work, but thats what I would try anyway.

nigelc116
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Joined: 22 Oct 2005, 17:47

Post by nigelc116 » 21 Jul 2006, 19:48

sub42

I was thinking the same way but what stopped me thinking that way was I thought this if the condenser insn't running at tick over then the pressure can't increase because the compressor isn't running to compress the gas.

I've looked at various threads and wiring diagrams on this and other sites and there is no obvious link that I can see between the engine revs and the air con compressor switch. - I'm now wondering if it's vibraion on a sensor wire that increases and the engine vibration increases

sub42
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Post by sub42 » 21 Jul 2006, 20:30

nigelc116 wrote:I was thinking the same way but what stopped me thinking that way was I thought this if the condenser insn't running at tick over then the pressure can't increase because the compressor isn't running to compress the gas.


Exactly. Thats on the HP side. The unit is going out on low pressure. There is not enough pressure in the system, or rather, that is what the LP switch guesses, and shuts down the compressor. The system thinks all of the gass is gone at low rpms. Just a guess....

Have you proved both the HP & LP switches in the three states, ie engine off, engine idle, engine running at 1500rpm? If you have not proved the switches in the different modes of running, then you will be running around in circles. They would be my next port of call. Incidently, you don't really need to know the state of the switches in a 'good' state. All you are doing is proving if one of the switches is changing state at higher or lower rpms. If one comes on or goes off once you are away from idle, then you might want to take a looky...

nigelc116
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Post by nigelc116 » 21 Jul 2006, 20:46

What I can't get my head around is...

If the Comp is off and the low pressure swithch thinks it's got no gas then when I raise the revs how does the pressure raise so that the switch changes state?

I can understand it going from high to low but not from low to high because there is nothing - as I can see it to raise the pressure because the comp is standing still.

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oscarloco
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Post by oscarloco » 21 Jul 2006, 21:30

I have the same problem and I figured out it has to be a faulty earth since everytime I give the compressor conector a good cleaning, compressor works fine for a while. When dirt and rust start accumulating, it starts failing sooner.

Also, if I have the lights on, aircon will work for a little while. Then I have to rev it hard to raise the voltage enough for the compressor clutch to engage.

sub42
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Post by sub42 » 21 Jul 2006, 21:36

As I said, just guessing. There must be something telling the compressor to turn on. So it's going to be rpm dependant, or its voltage dependant. Is the air-con on these things controlled by a box of tricks? Is it disengaging the compressor whilst waiting for something else to happen? ARRRRGGGHH! Nuts. I'm out, now I'm talking sh***e.

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oscarloco
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Post by oscarloco » 21 Jul 2006, 21:40

sub42 wrote:As I said, just guessing. There must be something telling the compressor to turn on. So it's going to be rpm dependant, or its voltage dependant. Is the air-con on these things controlled by a box of tricks? Is it disengaging the compressor whilst waiting for something else to happen? ARRRRGGGHH! Nuts. I'm out, now I'm talking sh***e.


I would go with voltage related. The Aircon brain is definetly telling it to turn on (the cockpit relay can be heard clicking and the fans spinning) but unless voltage is high enough to overcome the extra-resistance in the wiring, the compressor's clutch won't engage.

nigelc116
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Post by nigelc116 » 21 Jul 2006, 21:52

(the cockpit relay can be heard clicking and the fans spinning)


Where is the cockpit relay that you talk about the only relay that I've found relative to this is in the engine fuse box behind the battery.

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oscarloco
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Post by oscarloco » 21 Jul 2006, 22:35

In my ZX it's supposed to be behind the "glovebox".

James.UK
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Post by James.UK » 22 Jul 2006, 02:04

my knowledge of elecs is nil.. :oops: lol. but..

As the compressor has a elec magnetic clutch, presumably it wont work if the currant is too low. Soooo maybe it's related to that?? I.E. low revs = not enough currant to operate the compressor clutch?

nigelc116
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Post by nigelc116 » 22 Jul 2006, 12:14

The latest installment.......

I don't think that the problem is with the connection to the copmressor as the relay doesn't click in until the revs rise.

Having tested the switching side of the relay the voltage at tick over is 14.1 to 14.2 volts as per the alternator voltage at the battery. As the revs rise the voltage drops to 13.8 Volts but this could be a result of the comp running?

I've checked out the pressure switch and this works OK

If I bypass the switch by taking a wire direct from the battery to the switching wire on the relay then the comp runs all of the time, so this is what I have done.

The air con switch is still switching off the comp by switching off the 2 fans by the radiator and the ECU not allowing the comp to run until the fans are running.

I hope that I won't be causing any damage by having this permanently connected.

I suppose in hind sight I should connect this relay to an ignition switched wire but I can do this later.

I'm now suspecting the contacts on the air con switch inside the cabin above the radio.

Has anyone any thoughts on this.

sub42
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Post by sub42 » 22 Jul 2006, 18:44

Just so you know. Voltage and current are related. In laymans terms, the higher the voltage, the less current is required to do the same job of work. The lower the voltage, the higher the current, and hence why your voltage drops to nearly a volt less when the compressor is on with the fans. A one volt drop at 12volts is a lot of juice! If you have bypassed the pressure switch, and the unit works, then surely, it must be the switch? Did you bridge the switch, or did you hotwire it? I would have expected the switch on the dash to pull in the relay in the dash, and then the relay to pull in the fans and the pump?

nigelc116
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Post by nigelc116 » 23 Jul 2006, 08:40

I took a wire from a live item and connected it to the switching side of the relay, on my car this relay is in the engine compartment fuse box behind the battery.

I don't think that you can by pass the switch because the air con will be on all of the time, as the switch start up the fans at the front of the radiator.

alan s
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Post by alan s » 23 Jul 2006, 20:36

I've never ventured under the dash on my car to see what goes on there, but I understand there's a small fan there that circulates the air and sends the ambient air across the sensor thereby triggering the thermostat/sensor; have you checked that this is operating.
Also, if it's any help, here's a mod used over here on BXs that works quite well; we've done a couple of these now and it turns a BX system into a very efficient set up for very little cost. If it's applicable to a Xantia, I can't say, but may be worth investigating given the symptoms presently showing.

http://www.aussiefrogs.com/forum/showthread.php?t=9161


Alan S