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

[Doggy]

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.

[rwb]

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.

[Doggy]

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.

[Welly]

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.

[Welly]

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

[Doggy]

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).

[Doggy]

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.

[Welly]

Good advice form Doggy there.

[puggy]

The switch ...


and the reason a/c wasn't working gas was leaking through it


looking from front of car its on lefthand side of a/c rad near the top

[puggy]

Dont remove it you will lose all the gas , its one of those buy one just incase
when you take it off it is leaking followed by a re-gas !!

[gumby6371]

I'm watching this thread with interest as my AC hasn't worked since I've had the car.
I know precisely squat about AC systems, not even sure where all the bits are located under the bonnet.
If anyone fancies posting some nice engine bay pics with nice big idiot proof arrows and a simple check list then please do.
Also a guide to any checks using planet would be good.

Apologies for the hijack

[Welly]

I'm watching this thread with interest as my AC hasn't worked since I've had the car.
I know precisely squat about AC systems, not even sure where all the bits are located under the bonnet.
If anyone fancies posting some nice engine bay pics with nice big idiot proof arrows and a simple check list then please do.
Also a guide to any checks using planet would be good.

Apologies for the hijack

Basically:

Compressor (near alternator) turns low pressure refrigerant gas into a high pressure, high temp, liquid.....this goes through the Condenser (radiator-looking) up front and cools into a high pressure low(er) temp liquid it also has any moisture absorbed in the integral 'drier' (basically a desiccant bag)....then it reaches the Expansion Valve and Evaporator (like a heater matrix) the high press liquid passes through a tiny orifice (fnar fnar) into a large open space (the insides of the evaporator) [think: pressing on an aerosol can button] the liquid instantly vapourises back into a gas and absorbs heat in the process (it cools rapidly) the Evaporator goes very cold and air passing over it has its heat removed and thus provides cool air at the vents. The cooler low press gas then gets drawn back to the compressor and repeated....

It is important to remember that car a/c does not add cool air to the cabin but removes heat from.

[puggy]

Yes it is a pressure switch , if the pressure drops it shuts the system off .
There are several reasons for the a/c to not work , it took me £800 and dealing
with several so called profesional a/c technicians to sort mine out and it
was me that finally found the pressure switch was leaking .
You could start by finding a reputable a/c technician and having a re-gas because
they should start by emptying it and vacum testing it for leaks , you need to be there
so that if it is leaking you can tell them dont go any further . You then end up with
an empty system and they can put a dye in that shows the leaks , once you know
there are no leaks they can then re-gas if there are leaks change affected part while
system is empty then start again .

[Welly]

I have had a lot of experience with car a/c and have a range of T-Shirts available to mark various (expensive) mistakes, bullshitters, and other occasions. I too decided to take the bull by the gonads and find out the inner workings of such things for myself.

To that end I'm going to 'school' puggy (with utmost respect ) on his misinterpretation of the testing procedure; the system is firstly subjected to a nitrogen test at approx 300 PSi the operator will then observe the gauge watching for system leaks, obvious leaks will piss out and be accompanied by oil and dye leaks (seen via UV light and special spectacles) tiny leaks can be found by 'soaping' the joints and watching for bubbles.

Once the leaks are fixed ANOTHER test is done, then the system is held under Vacuum using a vac pump for at least 30 minutes this removes moisture in the pipework, any amount of moisture is bad for a/c and can cause blockages but under strong vacuum moisture boils-off and is recovered.

Once vac'd the new refrigerant, lubricating oil and dye is added and you're good to go.

[puggy]

I bow to your superior knowledge Welly