A/C not working... Evaporator temp @18C?

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A/C not working... Evaporator temp @18C?

Postby fattail95 » Sat Jun 14, 2014 10:58 pm

Hi Guys,

I got my new 406 a few months back now, and the A/C was blowing cool (not cold, but colder than the ambient temperature). I had it regassed, and it blew really cold for a little while. After 2 to 3 weeks however, the A/C was useless, far worse than it had ever been and no different with the A/C switched off...

So, I hooked her up to planet:

Image

I heard the evaporated temp should be around 1*C, but its nowhere near that - it sits at 18*C and hardly changes from that at all... Usually, I noticed when I turned the A/C on a clicking noise occured (a relay perhaps?), but it no longer does when I press the button, perhaps something to do with it?

Any help would be great!

Benjamin
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Re: A/C not working... Evaporator temp @18C?

Postby Doggy » Sat Jun 14, 2014 11:12 pm

The evaporator temperature should be about -1C.
I'm not familiar with the a/c diagnostics on a semi-mux car like yours - it may help if you can post the top items on this page, we can't see what the top two parameters are.

Possible reasons - you've either lost the gas again, the relay for the a/c compressor clutch is not being energised, or the contacts have failed.

I would be tempted to very briefly depress the filling valve(s), to see if any gas is released - it's the quickest thing to eliminate.
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Re: A/C not working... Evaporator temp @18C?

Postby rwb » Sun Jun 15, 2014 10:41 am

There may be a parameter called low pressure safety check which if activated means that the system is prevented from running because there isn't enough gas in it.

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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Sun Jun 15, 2014 6:17 pm

Here is all the data available on the A/C system:

Image
Image
Image
Image

Never does the evaporator temp drop below ambient air temperature... What is this compressor cut-off?

Another question... The turbo pressure reference value is always ~200mb higher than the measured value, is this normal? (The engine has been remapped):

Image

Sorry for the bombardment of questions.

Benjamin
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Re: A/C not working... Evaporator temp @18C?

Postby Doggy » Sun Jun 15, 2014 6:37 pm

Thanks for posting all of that.

Looking at the parameters,

Compressor Relay:- ON - and:
Authorisation Outout Compressor:- ON
mean it should be working, however:

Authorisation Input Compressor Cut Off:- Demanded suggests it's being disabled, but by what?

I can only think of low or high gas pressure - did you check if there was gas in the system?

I would need to see the same displays for a healthy example to spot the differences, but maybe someone else has previos experience?

Regarding the turbo pressure, a 110 will typically generate 1200 mbar actual at idle, vs a reference value of about 1000, (as it's a fixed geometry turbo), but the actual pressure should follow the reference value fairly closely above 1200 mbar. Bear in mind the instantaneous readings can be confusing since they're constantly changing and PP2k is only giving you a few 'snapshots' per second.
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Sun Jun 15, 2014 6:45 pm

RE the turbo pressure, it is always behind the reference value by around 200mbar until it hits max boost at ~2060mbar. At idle, it never generates any additional pressure over atmospheric, always sits at around 1040... Why would this be? An issue with the turbo not rotating freely? I have noticed oil residue at the bottom of the intercooler, could that be a leak?
Last edited by fattail95 on Sun Jun 15, 2014 8:54 pm, edited 1 time in total.
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Sun Jun 15, 2014 7:59 pm

Right, just pushed down a valve coming from a metal pipe near the battery tray (which I assume is for the A/C), and some gas SHOT out, really high pressure, so its not due to the lack of a gas...

I believe its something to do with the pressostat input (pressure switch input). It should be demanded when the A/C is running, as otherwise it would have no indicator as to what pressure the system is running at right? The engine load does not increase when the A/C button is turned on, and the clutch does not engage on the compressor, also there is no clicking from a relay which I used to hear... The fan however does come on at the usual low speed.

EDIT: What does demanded/not demanded actually mean in this particular situation? Does it mean on/off, or something else?
Last edited by fattail95 on Sun Jun 15, 2014 8:54 pm, edited 1 time in total.
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Sun Jun 15, 2014 8:15 pm

I've also just taken a look at the bottom of the intercooler. There is a fair amount of built up oil and grime at the bottom, and I noticed when you rev it hard the occasional tiny bubble comes along. Most (95%) of the oil looks old, as its covered in dirt, but by the location where the bubbles form it looks like newer oil. I assume there is a pinhole leak in the intercooler, causing the lower boost?
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Re: A/C not working... Evaporator temp @18C?

Postby Welly » Mon Jun 16, 2014 7:03 am

Puggy on here had a problem with the pressure switch itself (telling the ECU there was no gas when there was plenty) it's fitted on top of the condenser and part of the filter drier assembly, bit of a pig to get to I think you have to lean the condenser back or something. Be worth searching hos posts about it I think.
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Mon Jun 16, 2014 10:56 am

Would replacing the pressure switch be a wise thing to do, before looking at the BSI?

What does "demanded" actually mean in PSA lingo? Does it mean: required; on; needed; or what? "Not demanded" to me sounds like the ECU does not require a value for it, as if its not needed, but it could well mean that its not getting a value from it due to a fault.

Its booked in to the main dealer on friday, but would like to eliminate everything I can before hand.

Many thanks!
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Re: A/C not working... Evaporator temp @18C?

Postby Welly » Mon Jun 16, 2014 11:02 am

fattail95 wrote:
Its booked in to the main dealer on friday, but would like to eliminate everything I can before hand.

Many thanks!


Ooooh, careful there, they will most likely want to replace the whole condenser (300.00) then might move onto the compressor (£££££) have you read up about Puggy's threads on here about the switch?

'Demanded' means 'called for' i.e. the driver has selected a/c and therefore as long as there's enough gas in the system the compressor should start. High engine loads will disable the compressor temporarily, as will high coolant temps and also very low outside air temps will stop the compressor running to save on damage.

There were stories on here of a small relay inside the BSi which plays up and prevents the compressor running too.

Here's something I found: viewtopic.php?f=1&t=5445&hilit=pressure+switch#p53206
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Mon Jun 16, 2014 1:12 pm

Welly wrote:
fattail95 wrote:
Its booked in to the main dealer on friday, but would like to eliminate everything I can before hand.

Many thanks!


Ooooh, careful there, they will most likely want to replace the whole condenser (300.00) then might move onto the compressor (£££££) have you read up about Puggy's threads on here about the switch?

'Demanded' means 'called for' i.e. the driver has selected a/c and therefore as long as there's enough gas in the system the compressor should start. High engine loads will disable the compressor temporarily, as will high coolant temps and also very low outside air temps will stop the compressor running to save on damage.

There were stories on here of a small relay inside the BSi which plays up and prevents the compressor running too.

Here's something I found: viewtopic.php?f=1&t=5445&hilit=pressure+switch#p53206


If the pressure switch is not being "called for", could that mean that it is duff? The dealership are going to check the pressure switch as requested with a multimeter, what values should you be looking for?
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Re: A/C not working... Evaporator temp @18C?

Postby Doggy » Mon Jun 16, 2014 1:13 pm

The pressure switch is definitely a possible culprit - I would certainly try changing it before giving the main dealer a blank cheque.....

One point to watch out for - the 'pressure switch' or 'pressostat' is a different animal, depending on the age of your car.

Both Haynes and Autodata show the up to mid 2001 semi-multiplexed system. In this case the pressostat is a 4-terminal device with a common connection, one output via two normally closed contacts, (Hi and Lo pressure swithes)? to the BSI and two further outputs, via separate normally-open contacts, (one each for Hi and Lo pressure)? One goes to the fan low speed relay, (IIRC) amd the other to the A/c control module.

In the later, full-mux version, the A/c is managed by the engine ecu and the 'pressostat' is an analogue pressure sensor. You can monitor condenser pressure via the engine ecu. I beleive the engine ecu regulates the fan speed to control this varaiable, (in addition to coolant temperature). The evaporator temperature is controlled by engaging and disengaging the compressor clutch.

I believe both designs have a non-return valve fitted below the pressostat, allowing this to be changed without losing gas. When I replaced my condenser, I had to force the clutch on the first time, as the sensor could not 'see' the gas pressure, despite the system having just been filled. Once the clutch had been energised for a few seconds, everything then worked normally.

If it were my car, I would temporarily connect a 12V supply to the clutch, (taking care to get the right terminal on the 2-pin connector - one will show no resistance to the compressor casing, the other a few ohms) and prove whether the a/c works, (evaporator temperature drop). Don't do this for any longer than necessary to prove/disprovbe it works as you're bypassing all the safety interlocks.

Make absolutley certain you don't have a fuse gone anywhere.

Assuming the a/c works when you 'force' the clutch on, I would then try to prove whether the pressostat was the culprit, or try swaping it for one rescued from a scrappy.

When all other avenues are exhausted, I would set about replacing the relay in the BSi, (or more probably fitting another one externally).
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Re: A/C not working... Evaporator temp @18C?

Postby fattail95 » Mon Jun 16, 2014 1:18 pm

Doggy wrote:The pressure switch is definitely a possible culprit - I would certainly try changing it before giving the main dealer a blank cheque.....

One point to watch out for - the 'pressure switch' or 'pressostat' is a different animal, depending on the age of your car.

Both Haynes and Autodata show the up to mid 2001 semi-multiplexed system. In this case the pressostat is a 4-terminal device with a common connection, one output via two normally closed contacts, (Hi and Lo pressure swithes)? to the BSI and two further outputs, via separate normally-open contacts, (one each for Hi and Lo pressure)? One goes to the fan low speed relay, (IIRC) amd the other to the A/c control module.

In the later, full-mux version, the A/c is managed by the engine ecu and the 'pressostat' is an analogue pressure sensor. You can monitor condenser pressure via the engine ecu. I beleive the engine ecu regulates the fan speed to control this varaiable, (in addition to coolant temperature). The evaporator temperature is controlled by engaging and disengaging the compressor clutch.

I believe both designs have a non-return valve fitted below the pressostat, allowing this to be changed without losing gas. When I replaced my condenser, I had to force the clutch on the first time, as the sensor could not 'see' the gas pressure, despite the system having just been filled. Once the clutch had been energised for a few seconds, everything then worked normally.

If it were my car, I would temporarily connect a 12V supply to the clutch, (taking care to get the right terminal on the 2-pin connector - one will show no resistance to the compressor casing, the other a few ohms) and prove whether the a/c works, (evaporator temperature drop). Don't do this for any longer than necessary to prove/disprovbe it works as you're bypassing all the safety interlocks.

Make absolutley certain you don't have a fuse gone anywhere.

Assuming the a/c works when you 'force' the clutch on, I would then try to prove whether the pressostat was the culprit, or try swaping it for one rescued from a scrappy.

When all other avenues are exhausted, I would set about replacing the relay in the BSi, (or more probably fitting another one externally).


So I can remove the pressure sensor without having to degas the whole system? Also, is the pressure swich (mine is semi-mux, so no analogue for me) on the front of the condensor, or do I need to take the lights out to find it?

Many thanks everyone
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Re: A/C not working... Evaporator temp @18C?

Postby Doggy » Mon Jun 16, 2014 1:31 pm

IIRC it's at the near one or other bottom corner of the condenser, look for the wiring connector.

Can't honestly remember how accessible it is - I had the condenser out at the time.
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