That B****** Air con again

ghostrider · Post by **ghostrider** » 22 Jun 2005, 22:17

OK so I've saved my dosh and got a really good local guy out to regas today, He vacced it out, flushed with nitrogen, tested for leaks using, I believe the nitrogen and when he was satisfied that there were no leaks after an hour or so he added new lubricant and regassed. So far so Good.
I start the engine hit the A/C button....... NOTHING[:(] [:(]. Check that the fans run OK no problem there.
So I checked the pressure switch, thinking I'd just paid a whole load to get a refill which I would lose if there was a problem. There is continuity between contacts 1 &2 which are where the thicker pair of wires go to. So Switch OK at least as far as getting it going, no continuity between 3 & 4.
I then check to see if there is any voltage on either of the wires going to 1 & 2 which there isn't, 12v on 3 only. If I remove connector to the pressure sw and connect 3 to 2 compressor runs fine. So there should be 12v on wire 1, next suspect is that bitron control unit, remove headlight use large hole saw to cut hole in glassfibre panel above unit so I can get it out without dismantling the front of the car again.
Getting Bitron unit apart none too easy, I check for the dry joint as on th Peugeotlogic site (which I see is due to closedue to a lack of help from anyone [:(][:(]) first thing is my unit is all solid state, no relay as described, and none of the wires going to it look heavy enough to carry large currents and no power transistors just an ic and several small discrete transistors, so it looks like the relay is now in some remote location but Where?.
Put the whole lot back together and having seen the ECU reset bit with battery disconnected for a bit, I thought that it might have reset itself.
Which to an extent it had... hit aircon switch, fans run half speed and some seconds later the aircon starts up [8D] [8D], icy cold [:D][:D], great thinks I its fixed, only trouble is it only works on tickover, the second you open the throttle it stops, faulty compressor clutch thinks I but no, if I monitor the voltage on pin 1 of the pressure switch (supply to compressor) the second the throttle opens the voltage is cut off, now my rev counter is intermittent and only works when the engine is cold, does the rev counter sender do something to the ECU?
The other possibility is that the water temp sensor is activating the aircon cutoff relay prematurely but it seems odd that it seems so throttle position oriented, firstly where is that relay? as it appears not to be one of the three between the 2 cooling fans.
Any thoughts people? thanks in advance
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Chris Peddie · Post by **Chris Peddie** » 23 Jun 2005, 13:19

Mine seems to be doing the same thing (see post 'Injector pump microswitch' on the Citroen forum) but only once the car has been sat in the sun all day. First thing in the morning it seems to work properly. My rev counter doesn't work at all, so that might not be your problem, but then again mine doesn't have an ECU.
The aircon works at tick-over, but cuts out as soon as the microswitch on the pump is switched by movement of the accelerator arm. If I tie this switch closed (at the idle position) the aircon works fine.
Maybe you could try this to see if we both have the same problem? I haven't yet found a feed from this microswitch to the Bitron unit on any of the Haynes electrical diagrams or the ones they sent me specifically for the aircon circuits ... ...

alan s · Post by **alan s** » 23 Jun 2005, 14:26

Just a thought (guess) but if the gas level was low, it may just be that as soon as the revs increase, the pump increases its volume, reduces the backpressure to below the level required for the LP switch to stay in circuit and it simply open circuits as it's supposed to do to prevent going into vacuum.
If the mnechanic fits a compound gauge to the suction service valve when it's running this would answer that question.
That's basically looking for a possible mechanical cause rather than an electrical one and does answer to reason.
Alan S

ghostrider · Post by **ghostrider** » 23 Jun 2005, 23:31

Chris, wish I'd read your post first [:D] [:D] [:D], yup the throttle position switch certainly turns it off, holding the switch closed enables it to run OK. Two questions then 1. what function does that switch perform,( other than wasting loads of my time [:D] [:D] [:D] ) and 2 how does it tie in to the aircon?. One other point from my investigations today, the famous (?) Bitron control unit which on mine is all electronic controls 2 relays in the fusebox under the bonnet, mine are bright purple in colour and situated on the extreme RHS of the box as you look at the car, the throttle position switch also operates these relays which I presume provide power to pin 1 of the pressure switch.
Alan, the guy who regassed me had two gauges attached to the compressor one showing vacuum the other showing positive pressure, he was satisfied that the readings were correct bearing in mind the constraints imposed by the compressor disengaging off tickover, we ran the air con flat out on tickover for about 10 - 15 minutes and it functioned fine. He has already volunteered to return and carry out the final checks once I've sorted the electrical gremlins and in the meantime is making enquiries of colleagues as to whether anyone can shed some light on the subject.
Having now invested over ?450 getting to this point I have bitten the bullet and ordered the Lasertec manual, so that hopefully I will finally have an accurate wiring diagram. The BX, AX and XM bits come with the unlock code so if you need any info from it, if there is some way of copying it I can E- mail it to you or post it here somewhere maybe? I haven't received it yet, the demos that I downloaded were very similar in detail and presentation to that of my CX official workshop manual so at the moment I have high hopes that it will be of use [:D] [:D] [:D]
back to the grind, at least I've been able to Waxoyl some of the large size hydraulic pipes (VSX) which are rotting away nicely just like my good old DS. Plus ca change! as the French would say
Pete
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alan s · Post by **alan s** » 24 Jun 2005, 05:37

Another thought of course could be moisture in the system which can cause ice to build in the oriface of the T/X valve and cause the system to pump into vacuum which would immediately cut the power to the clutch.
It may be an electrical problem, but in all honesty, most problems associated with air/conditioners in cars can mostly be attributed physical and mechanical problems causing various controls and safeguards to come into play.
I would firstly get him to put his gauges on the system whilst it is running or it's just a hit and miss guess rather than a systematic troubleshooting and the gauges will tell the story as regards the internal operations.
Lack of gas or moisture will show as low back pressures; low gas will show as soon as the compressor cuts in whereas moisture will show it all going correctly but then will suddenly drop and the clutch cut out.
Faulty switch or wiring should then be evident if these aspects are taken out of the equation.
Alan S

ghostrider · Post by **ghostrider** » 24 Jun 2005, 16:32

Alan, given that it only worked on tickover, the guy had the gauges on it whilst it was running, and seemed satisfied that the readings were correct after running it flat out for 10- 15 minutes I know the compressor was not turning very quickly, the pressure switch still only has continuity between pins 1 & 2 even when the clutch drops out, if icing were the problem wouldn't that show up even if the compressor was only turning slowly, given that it was a hot day (30c) and the inside of the car got down to about 8c at a guess. The other thing is that if you remove the switch on top of the injection pump and operate it manually the aircon cuts in and out with the switch without the engine speed changing, which seems to be at odds with the idea that as the compressor speed picks up the faults you describe will come in. I also fitted a new dryer bottle before the recharge, so surely it must be capable of taking some moisture out of the system? When the original leak occured , I removed the pipes and blocked all the open ends off with rubber bungs within about half an hour. Which device detects the vacuum you describe and cuts the power? and secondly where is it so I can check it? Thanks for all the guidance, perhaps I should do a course on auto aircon [:D] [:D]
Chris the only thing I've noticed with tying the switch up is that it only works for a while!
Pete
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ghostrider · Post by **ghostrider** » 24 Jun 2005, 17:13

Ok here are some figures I've just obtained with the microswitch tied up and engine running at a steady 2500rpm for 30 mins engine temp (according to gauge) 80c, oil temp 95c. Outside temp 28c humidity 98%. Inside car temp 8c temp of air coming out of facelevel vents 3.5 to 4.5c, with the temp control on full cold, fans to auto, and recirculate. I don't know how good this is but if I could get it to work like this without that switch tied up it would suit me[:D] [:D]
Pete
sorry if this is a double post, but for some reason if I hold my backspace key down too long it submits the post ...... weird
Pete
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ghostrider · Post by **ghostrider** » 25 Jun 2005, 13:57

Kowalsi has generously sent me some wiring diagrams for the system,
The triple pressure switch gets its voltage to operate the compressor , from either the Bitron unit or the A/C control unit, and the compressor clutch relay is controlled by the engine ECU, I've not checked yet whether the A/C cutting off is due to voltage to that relay being cut off by either the Bitron or the A/C control or whether the relay is being pulled in by the engine ECU to achieve the same effect, so out with the voltmeter this am, but my guess is that as that switch on top of the injection pump is involved it's something to do with the ECU. It can't be the coolant sensor as the problem exists with the engine hot or cold, unless of course the sensor is out of its range.......
Report back later
Pete

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