picasso aircon problem

dave.b · Unread post by **dave.b** » 07 Aug 2006, 20:36

hi, sorry for the long winded question, but i thought it best to try and explain the problem fully.

i have a citroen picasso 2.0 hdi and the aircon does not work. it originally had a leak and i have replaced a pipe and the condenser, it now holds pressure fine but the compressor clutch does not cut in and the cooling fan does not start when the aircon is activated, although the light on the switch does come on.

i have checked all the fuses and allare ok, a faulty pressostat has been suggested and i was advised to test this by bridging the input plug at pins 1 and 2 which would give a gas ok signal and start the fan and compressor clutch (not sure if it should be pins 1 and 2) all this did was start the cooling fan at fast speed i think? even without the aircon switched on but nothing from the compressor.

i should add that the compressor clutch does work when given a separate live feed.

any suggestions welcome as there cant be too much of this warm weather left!

cheers, dave.

JohnD · Unread post by **JohnD** » 08 Aug 2006, 09:03

Is the gas pressure OK? The compressor clutch won't cut in if the gas pressure is low.

Clogzz · Unread post by **Clogzz** » 08 Aug 2006, 14:54

If the cooling fans went to the high speed, it means that you bridged the wires that are meant to sense high pressure in the system.
Think that the compressor clutch wires are the 2 thick ones.

dave.b · Unread post by **dave.b** » 08 Aug 2006, 20:11

hi guys, thanks for the replies,

ref the gas pressure it was when the system was being filled that the compressor clutch problem occured as the system was switched on to pull the remaining gas in and did not start as it should. as things stand i believe the system is still pressurised but am waiting to confirm this with the guy that was filling it.

what i was trying to prove was if there was a fault in the wiring or the pressostat switch and i was told by bridging the plug that even if there was not enough pressure in the system it would fool the brain into thinking there was.

if it worked then it would point to a faulty pressure switch, and if not maybe a wiring problem. but as you say i dont think pins 1 and 2 were the correct ones.

ref the 2 thick ones (one may be me!) the four wires are the same size and i do not want to try bridging just any but from the haynes wiring diagram:
no1 is from the aircon fuse (and does carry 12v)
no2 goes to the engine management control module
no3 goes to aircon fan relay
no4 goes to bsi

there you are, clear as mud!

Clogzz · Unread post by **Clogzz** » 09 Aug 2006, 13:49

This map is from the Xantia.
Lower left shows pressure sensor switch pins.
Pins 1 & 2 are low and high pressure cut-off.
Pins 3 & 4 are normal pressure switch.

Edited on 10th August to add second map.

dave.b · Unread post by **dave.b** » 10 Aug 2006, 23:32

the xantia appears to differ from the haynes picasso wiring diagram which i am trying to post here but having no success will try again tomorrow[/img]

dave.b · Unread post by **dave.b** » 11 Aug 2006, 21:21

[img][img]http://f10.putfile.com/thumb/8/22216002447.jpg[/img][/img]
wow! eventually it worked

not the aircon but the posting of the image

hopefully you will be able to see that the wiring appears to be different from the xantia although the wiring diagram i have posted does not appear to be as complete or such good quality as the one you have.

any advice to help prove where the fault is would be appreciated.
thanks, dave.

Clogzz · Unread post by **Clogzz** » 12 Aug 2006, 16:01

Clear as mud the diagram too !

Try bridging pins 1 & 4 on the pressure switch.
That will tell the BSI that there’s no low or excessive pressure in the system.
If nothing happens, the one thing left to try is to join pins 1 & 3 to see what it makes of it.
There’s no risk of fireworks, because pins 2, 3 & 4 are all provided to join pin 1.

dave.b · Unread post by **dave.b** » 12 Aug 2006, 22:40

thanks for that i will try tomorrow and post results

dave.b · Unread post by **dave.b** » 14 Aug 2006, 20:15

no chance to check on sunday as it didn,t stop raining all day, checked today and encouraged by results.

linked pins 1 and 4 as suggested and if the internal fan is switched on then when you switch on aircon the compressor and cooling fan both start. (my understading is that the internal fan should start automatically when aircon starts)

system must be pressurised still as there was chilled air coming through at this point. 8)

if the internal fan is switched off when you switch on aircon then nothing happens until the internal fan is manually started at which point the compressor and cooling fan again start.

linking 1 and 3 does not appear to have any effect.

i assume from this that it is likely to be a faulty pressostat? is it advisable to leave pins 1 and 4 linked until i replace the pressostat maybe only to use the aircon for short spells due to the safety aspect of the pressostat?

thanks for your input so far, i finally feel i am getting somewhere.

Clogzz · Unread post by **Clogzz** » 15 Aug 2006, 14:58

The sequence is that the internal fan must be turned on first, with the fan speed controller.
After the internal fan spins, turning on the air conditioner will start both cooling fans at the low speed, and next, the aircon compressor kicks in.
Turning on the air conditioning will not start the internal fan.
Unless the internal fan is turned on manually, the aircon won’t start either.

It does look like a faulty pressostat, especially if the fault is there all the time, even with cold engine and air conditioning circuit not having had time to produce excessive pressure.
Don’t know much about the circumstances and cause of excessive pressure, but it’s certain to be explained somewhere in this aircon forum.

I wonder if overfilling the system with gas may cause high pressure.
The pipe from the condenser to the evaporator getting fairly hot may also be an indication of high pressure.
I’d say that you’re safe to bridge pins 1 & 4 for as long as the condenser and top hose to the evaporator aren’t getting too hot.

dave.b · Unread post by **dave.b** » 15 Aug 2006, 23:21

thanks for that, from what you say it all appears to be working correctly except for the pressostat.

i have ordered one today but will take a couple of days to arrive, i did also try removing the old one today and expected a small amount of gas to escape

as it was unscrewed because the valve should close as it is removed? this did not seem to be happening and as the gas showed no sign of slowing i quickly screwed the pressostat back on.

it looks like i will have to change it at the same time as i get the system recharged.

Clogzz · Unread post by **Clogzz** » 16 Aug 2006, 13:40

Yes, there’s meant to be a so-called ‘Schrader’ valve, to prevent the gas from escaping.
Don’t understand what’s going on here.

There’s certainly no way to unscrew the wrong thing.
So, it’s either a faulty valve, or a dubious dryer bottle without valve, not likely on a recent car.
Plenty of relevant context here:

http://www.frenchcarforum.co.uk/forum/v ... hp?t=19693