Simon's new Xantia V6 and Leaf blog

[white exec]

Hope helpful...

[Mandrake]

Hi Chris,

Referring to the first circuit you posted, here is how I think it's supposed to work...

8007 is the pressure switch which is a 4 position double pole switch. (I did not realise that until seeing the diagram, I thought it was two different switches) It is shown in the "normal pressure state". Imagine the pressure diaphgram in the switch pushing the switch contacts from right to left as pressure increases. So there are 4 different pressure ranges the switch can report.

The middle two contacts control whether the compressor is allowed to engage or not and the outer two contacts control whether the fan is boosted to high speed.

8080 is the Climate ECU, pin 6 is the control signal to activate the air conditioning compressor based on the dashboard switch position, temperature sensors etc. This goes to pin 5 on 8010 which I believe is the Bitron unit which controls the fans. This is what switches the fans on to low speed when you turn on the A/C. Note that even if you unplug the pressure swich (thus disabling the A/C clutch) the fans will still run at low speed when you turn on the A/C button.

This signal also goes to pin 3 on relay 8015, then on to the middle contact of the pressure switch then to pin 3 on relay 8005, then to Pin 1 of 8020 which is the compressor clutch solenoid.

The point of all these relays and switches is that there are three different things which can disable the compressor clutch even when the Climate ECU is commanding it to be on - if the pressure in the system is very low or very high the middle contacts of 8007 will go open circuit and disable the compressor.

Relay 8015 is under the control of pin 11 on the Bitron unit and I'm pretty sure this is to allow the Bitron to disable the A/C if the coolant temperature of the engine is extremely high, (since the A/C adds additional heat load to the radiators) while relay 8005 is under the control of the engine ECU and I believe is used to temporarily disable the A/C when you floor the accelerator. (Not really needed on the V6 but carried over from other models ) The signal on pin 3 of relay 8005 is also sent to the engine ECU so that it knows when the compressor is engaged so that it knows when to boost the idle to compensate for the extra accessory load.

The outer contacts of switch 8007 simply connect 12v from F2 to pin 13 on 8010. (Bitron) This puts the fans into high speed mode.

Now its clear how the four pressure switch states fit in:

1) Far right - very low pressure. Both switches open circuit, A/C clutch disabled, fans on low speed. Same result when unplugging the switch.
2) 2nd from right - normal pressure. A/C compressor allowed to operate, fans on low speed.
3) 3rd from the right - elevated pressure. A/C compressor allowed to operate, fans go to high speed.
4) Far left - excessive pressure. A/C compressor disabled, fans remain on high speed.

From this, and the fact that I have owned three Xantia's now which didn't go straight to high speed fan on A/C, I'm going to reiterate that it's NOT normal for the fans to go directly to high speed when the A/C is turned on, unless the engine radiator or A/C condensor are very hot and/or the pressure in the system is too high. (or the pressure switch is faulty)

It simply makes no sense to have a mode (even shown as the default in the wiring diagram) where the A/C can run with the fans at low speed if the pressure is going to be high enough to always trigger the high speed mode.

I'll check it again in the morning when it's cold to see how it behaves, also I can unplug the plug, bridge the two middle conections to make the compressor run and see if the fans do or don't run at high speed mode when the outer pins are bridged. I can also measure the contacts on the switch under this test condition to see what the switch is reporting.

Either the radiators were unusually hot when I got back home or I think there has to be a bit too much pressure in the system or a faulty switch. If the switch is indeed comanding the high fan speed on it might be worth me trying to get hold of a replacement switch because as mentioned I've had a faulty one on a previous Xantia where it was not activating at the correct pressures.

[Mandrake]

Pressure switches:

https://www.mister-auto.co.uk/high-pres ... 1997-2003/

[white exec]

Hi Simon,
Couldn't sleep for thinking about this, so revision; two posts of mine above deleted.

Here's how the two fan speeds are achieved:

Slow speed - fans in series
Line 809A on ECU (WTCU #8010) goes to Gnd.
Switches on RLA #1500C
Fans put in series
(RLAs 1500B and 1500A remain off)

Fast speed - fans in parallel
Line 809A remains Gnd'd
Line 8091 also becomes Gnd'd
RLA 1500C remains on
RLAs 1500B & 1500A come on
Both fans operate in parallel, full speed

Sanity restored.

Only ?? is the connection to the auto 'box...
Looks like an input, from the arrow.
A request (Gnd signal, and direct into the slow-speed relay) by the 'box for Slow speed fan running? Transmission cooler?

Possible fault conditions

If Slow speed were to fail to operate (RLA 1500C malfunctions)
and coolant temp rose to bring on RLAs 1500B & 1500A
then only one fan (1510B) would operate, at Fast speed

If the correct 5-pin (c/o) relay were not used in the 5-pin slot, but the relays got switched around
- Slow speed would operate normally
- Fast speed would operate on one fan only (1510B)

[Mandrake]

Sorry to keep you up worrying that wasn't my intention.

I think you're looking in the wrong place though - the fan controller is working fine - low and high speed fan modes operate normally in response to engine coolant temperatures. It's only when the A/C is turned on that the fan was going to high.

I'll try to get outside a bit later today to do some proper testing and measurements. The more I think about it the more I think I've got a faulty or worn out pressure switch.

Inside there must be a spring or diaphragm of some kind which pushes back against the gas pressure - if that spring has broken or otherwise gone weak with 23 years of aging the switch will respond at a lower pressure than it should, thus triggering the high speed fan mode prematurely. I think it could be as simple as that, and a new switch isn't that expensive, certainly compared to the AC repair itself... so if I confirm that it is the switch triggering the high speed fan mode I'll take a punt and order a switch. They're easy to replace since they're self sealing when you unscrew them, a bit like the head on a hand held butane torch.

[white exec]

I was only concerned to understand where the two fan speed signals emanated from, so that that bit of the system could be checked.
Seems that, over time, there were several slightly different triggers for the usual three relays, and I just wanted to be certain which one was operating here.

Wonder what that Gearbox input is? You had some work done on it recently.

[Mandrake]

Wonder what that Gearbox input is? You had some work done on it recently.

The gearbox ECU is able to bring the fans onto high speed based on gearbox oil temperature. However the oil has to be pretty hot for this to happen, I think about 110C! It's in the 4HP20 training manual somewhere..

[CitroJim]

Wonder what that Gearbox input is? You had some work done on it recently.

The gearbox ECU is able to bring the fans onto high speed based on gearbox oil temperature. However the oil has to be pretty hot for this to happen, I think about 110C! It's in the 4HP20 training manual somewhere..

it is and the gearbox will also drop into a special map to help the oil cool down too...

[Mandrake]

Ok I've been out doing some testing and measuring and confirmed my suspicions - it is indeed the high pressure contacts in the switch triggering the fan high speed.

Before I go any further I should point out that when I was referring to "middle" and "outside" contacts on the switch plug in earlier posts I was in fact wrong - as they're actually numbered 3-1-2-4 on the circuit diagram, so sorry about that confusion. In fact it's two end contacts with thick wires which enable the compressor and the two skinny wires on the other end which enable high fan speed.

With the engine cold I was only able to run the AC with the blower fan on high for less than 3 minutes before the radiator fans went to high speed - by that time the engine radiator was still cold so this is definitely not normal behaviour based on my previous Xantia's.

To confirm it was the pressure switch I unplugged the switch, bridged the contacts to the two thick wires to allow the compressor to run, then put a multimeter on the high pressure contacts of the switch and sure enough after a short time running the contacts closed. (Also bridging those two pins on the plug makes the fans come onto high - even if the AC is turned off!)

So definitely the increase in pressure triggering the high pressure contacts in the switch causing the fans to go to high speed. With the blower fan on minimum (and therefore ambient air not adding much heat to the evaporator) the evaporator was able to get down to near 0C and the radiator fans remained on slow:

However if I turned the fan up a bit the evaporator temperature went up and fairly soon after the radiator fans went to high speed. Here it is with the blower fan on full:

So either the pressure switch is faulty and triggering too soon or the pressure is genuinely too high. I can understand the fans going to high on a 25C day with the engine hot from motorway driving, but with a cold engine just a few minutes from starting up the fans should not be going to high for the AC - never did on this car before, nor on my other two Xantia's. High fan speed makes a lot of noise so is something easily noticed!

The pressure switch is a cheap and easy swap to rule out first so I'll order a switch and swap it over to see if it makes a difference. If it doesn't I might need to have a chat with the garage.

[Mandrake]

Wonder what that Gearbox input is? You had some work done on it recently.

The gearbox ECU is able to bring the fans onto high speed based on gearbox oil temperature. However the oil has to be pretty hot for this to happen, I think about 110C! It's in the 4HP20 training manual somewhere..

it is and the gearbox will also drop into a special map to help the oil cool down too...

OMG, a Citrojim sighting in my blog! That must be worth more than a rare car sighting!

Good to see you around again Jim.

[CitroJim]

OMG, a Citrojim sighting in my blog! That must be worth more than a rare car sighting!

Good to see you around again Jim.

Seems I'm back Simon

Delighted to see you are here and still have your V6 Excellent!

Lots to catch up on but over the coming days...

[white exec]

OK, that's the gearbox input explained. From the circuit, it will be Slow speed that the 'box will trigger, by directly grounding the relay. Hope the new pressure switch does the trick.

[Mandrake]

Seems I'm back Simon

Delighted to see you are here and still have your V6 Excellent!

Lots to catch up on but over the coming days...

Yes I still have it, I thought the gearbox was a gonner recently though, twice! Lots to catch up on indeed. Here's a lightening round...

About six months ago the gearbox started exhibiting "flare ups" on upshifts and other erratic behaviour... Thinking it was on borrowed time and with nothing to lose I did an oil change (it has had a few before this) and added a bottle of Lubegard Red at the same time, which has worked well for me before. It took maybe a couple of thousand miles over a few months as it doesn't get much driving but I recently realised the flareups on upshift have gone. Phew!

Then about 6 weeks ago when I needed the Xantia while the Ion was broken down I thought the gearbox was dead again because it wouldn't engage reverse at all!! It was several days before I had time to look at it but the Lexia showed that the ECU wasn't reading the gear position switch correctly! I initially diagnosed the switch, ordered a replacement but it didn't solve the problem! It later turned out to be white corrosion on the ECU connector located under the battery tray...

After I cleaned that all up and greased the connector slightly so that it engaged more positively the problem was gone. I also found I had to tweak the adjustment of the gear selector cable slightly to get it working just right. No problems with the gear shifter since then.

While I was trying to find the gear selection problem I inadvertently found and fixed another - one of the fuses was missing in the under bonnet fuse box, and turned out to be the fuse that provides the permanent live power for the gearbox ECU memory! Without it every time the key was turned off the gearbox ECU would immediately lose power and not be able to save any auto adaption information as that information is only saved 20 seconds after the key is turned off to reduce eeprom write cycles...

That explains why the auto adaption to gearbox characteristics didn't seem to be working - gear changes have been a bit abrupt for a long time (especially engaging reverse which would really slam into gear) and have never really settled in, because every time the key was turned on it would come back to the same default state having forgotten what it learnt on the previous driving session...

I just drove the car yesterday after picking it up from the aircon repair and both the engine and gearbox are running fabulously, the gearbox seems nice and smooth and the motor is very peppy, more than it has been for a long time.

I actually have a theory that the clattery, failing aircon compressor which has been noisy and on the way out for the last year or two was generating so much vibration and mechanical noise when engaged that the mechanical noise was passing into the engine block (as it seems to be bolted hard to the engine without rubber mounts) and triggering the engine knock sensor falsely! This could have the effect of retarding the ignition timing attempting to prevent engine knock that didn't actually exist... The new compressor is of course nearly silent...

I'm having an interesting problem with the fan speed coming onto high with the aircon which I'm now looking at which is the current issue being discussed.

Another niggle it has to try to sort out during this lockdown period is the front suspension is intermittently a bit harsh - I think the electrovalve may be playing up, either that or the ride height is not being regulated properly. Haven't had a chance to look at that seriously yet.

[Zelandeth]

Shame there's not an easy way to measure the condenser temperature...can work out the pressure based on that.

Evaporator temperature sounds reasonable, 6C will equate to 38psi which is reasonable (assuming the system has been charged with R134a anyway).

[Mandrake]

Shame there's not an easy way to measure the condenser temperature...can work out the pressure based on that.

Evaporator temperature sounds reasonable, 6C will equate to 38psi which is reasonable (assuming the system has been charged with R134a anyway).

The invoice lists R134a as the gas used.

Would an IR gun pointing at the condensor give a useful reading ? Not sure whether its aperture is narrow enough to look through the front grills at the condensor without removing the grill though. Also not sure how accurate the reading would be with an unknown emissivity of the radiator fins - although I suppose I could calibrate it at ambient before starting it up as my IR gun has an emissivity calibration adjustment.

(Edit: never mind, I just realised the fans are in the way too as they're on the front)

Do you happen to know what the normal pressure range is at the drier bottle measurement point both when the system is off and when it is active ? (Trying to get an idea how critical / non-critical the pressure is) Also is there any possibility that there is a blockage somewhere in the system like the drier bottle that could be restricting flow and causing excess pressure increase ?

Mind you if there was a blockage I would imagine that the vent output wouldn't get very cold. Even with the blower fan on full speed the air through the vents feels very cold, certainly a lot colder than it was back when the old compressor was working. And with reduced blower fan speed it can easily get down to 0C. (In fact the compressor cycles off and on with the fan on minimum)

The pressure switch is ordered but it's going to be about 7-10 days before it arrives so I won't really know any more until then. There is plenty of other fettling and cleaning to be done on the car in the meantime though!