Locating part for air con

[Mandrake]

Hi Clogzz,

Eureka!

I'm pretty sure I've at last found the problem, and it could be as simple as the gas pressure being a bit low.

Now that I know what the purpose of the different contacts are on the pressure switch on the dryer, I left my multimeter in the car awaiting a time when the aircon would fail to work.

This morning it failed to work, so out with the multimeter pronto, and yep, you guessed it, the "normal pressure" pair of contacts (the one that activates the compressor clutch) was open circuit.

So I bridged those contacts on the plug with the meter in 10 amp mode - 3 amps flowed and the compressor clutch came on, and after 10 seconds the air was cool.

I then measured the contacts on the pressure switch and sure enough, after only a few seconds of the compressor running, the contacts were now closed, indicating enough system pressure, and after plugging the plug back in it continued to work.

So the problem is obvious - its either (a) pressure switch is dodgy, or (b) genuinely borderline pressure in the system preventing the compressor from being allowed to turn on.

It makes a lot of sense now - if the pressure is borderline for triggering the pressure switch (whether it be due to genuine low pressure, or a dodgy pressure switch) that explains why it wont work sometimes - the pressure will change a bit with ambient temperature and engine temperature.

Usually when it fails to turn on initially, after 10 minutes driving it will start working, and I guess that the engine radiator is heating the aircon one, and causing a slight increase in pressure enough to trip the pressure switch...(or perhaps even just driving vibration)

Once its going it usually keeps working, since the operating pressure will be higher than the non-operating pressure - so its self sustaining.

I guess the thing that made me discount low pressure right from the beginning was the fact that when it did work, it works really well - 10 seconds and its ultra cool.

I guess I assumed that if it really was low enough in gas to not activate the pressure switch sometimes, that it wouldn't cool very effectively...of course if it actually is the pressure switch faulty rather than low gas pressure, that makes sense too...

Unfortunately it now means I have to take it to a professional, as I can't test or replace the pressure switch myself, nor can I test or gas the system pressure...

Thanks all...

Regards,
Simon

[Mandrake]

While I'm at it,

I had a look at the aircon on my Dad's Xantia, and have learnt a little bit about its problems - basically the pressure switch is always indicating sufficient pressure (contacts measure closed) and the compressor clutch *always* works, unlike mine, and there is even activity in the site-glass when it is running, however there is no cooling whatsoever.

Today I noticed that on the two steel pipes on the compressor, on my car the left hand one (looking into in the engine bay) gets hot and the right hand one gets icy cold. On Dad's one, the left hand one gets hot (possibly even hotter than mine) but the right hand pipe stays at ambient temperature.

Any ideas what that might be ? Some kind of blockage somewhere ? Or could it be really low in gas ? (But if so, why is the pressure switch allowing the compressor to come on...)

Regards,
Simon

[alan s]

The hot pipe is the discharge pipe taking the gas to the condensor to give up its heat so if that pipe isn't hot, the air con isn't cold.
The other pipe is the suction pipe and if it is ambient to cool (as in sweating) that is normal but if it's freezing, that's due to several possible causes including leaking valves in the compressor, T/X valve not shutting off or the most common, too much gas in the system.


Alan S

[Mandrake]

The hot pipe is the discharge pipe taking the gas to the condensor to give up its heat so if that pipe isn't hot, the air con isn't cold.

The hot pipe is hot though - its hotter on his car than on mine in fact.

The other pipe is the suction pipe and if it is ambient to cool (as in sweating) that is normal but if it's freezing, that's due to several possible causes including leaking valves in the compressor, T/X valve not shutting off or the most common, too much gas in the system.

Ok well on mine that pipe is "cool" enough so that it gets condensation on it... I was perhaps exagerating when I said icy cool.

On his one, that cool pipe is strictly ambient temperature - no change whatsoever when the compressor is turned on....

Which means............. ?

Regards,
Simon

[alan s]

The heat of the discharge pipe on any system is governed by the amount of heat it's drawing from inside via the evaporator.
As regards the suction line, there's several variables that you wouldn't be able to answer without either physically inspecting or putting a set of gauges on it such as: Is it on R12 - R134a or MP52 Suva or varient? Has it got a 134 T/X operating on 134 or an R12 one?
As I say, the T/X should chop the gas off at the outlet to the evaporator if all things are operating correctly and in the advent of a 134a conversion, the charge should be nominated charge (ie) 1KG less 10% although 800 grams is what most seem to be happy with.
If the frost line isn't cut at the outlet, then leaky T/X or overcharge of gas is the usual culprit unless someone's done something a bit radical with the plumbing.

Alan S

[Mandrake]

The heat of the discharge pipe on any system is governed by the amount of heat it's drawing from inside via the evaporator.
As regards the suction line, there's several variables that you wouldn't be able to answer without either physically inspecting or putting a set of gauges on it such as: Is it on R12 - R134a or MP52 Suva or varient?

The car is a 1994 and the compressor is clearly labeled as R134a

Has it got a 134 T/X operating on 134 or an R12 one?

No idea

As I say, the T/X should chop the gas off at the outlet to the evaporator if all things are operating correctly and in the advent of a 134a conversion, the charge should be nominated charge (ie) 1KG less 10% although 800 grams is what most seem to be happy with.
If the frost line isn't cut at the outlet, then leaky T/X or overcharge of gas is the usual culprit unless someone's done something a bit radical with the plumbing.

Alan S

Unfortunately thats all technospeak to me...

Regards,
Simon

[Clogzz]

Hi Simon,

Nice to read about progress.
It does look like the gas pressure is getting a bit marginal.
If it was outright low, then the low pressure contacts would prevent the compressor from starting.
Since it’s the normal pressure contacts that don’t always close, it must be an indication that the sensor switch is working normally.

On this previous photo of your engine bay, the sight glass on the dryer bottle has gone opaque, and so has mine.



That may indicate moisture in the system.
Alan should be able to enlighten us on that one, and Hello Alan, and many thanks for the valuable information posted.

When all is normal, when you switch the air conditioning on, there should be a few small bubbles in the other sight glass at the top of the bottle.
Mine is constantly frothing brownish, but there’s still plenty of cold air coming in.
I’ve only had one instance yet of the aircon not coming on, and switching it on a second time made it come good.
Just noticed too, that the plastic above the aircon switch gets fairly warm when the aircon is on.
That must indicate that the current flows through the switch.

One thing that worries me is that the aircon plugs face down, meaning that the regasser will have to access them from underneath.
Don’t know if they can be trusted to jack up a Citroën properly.
I'm thinking of normal height setting with the wheels hanging.

Also seeing that on your picture, we can see the pavement under the car.
Isn’t there meant to be a plate under there ?
Mine is the same, see-through to the ground, but what’s this then:

dead-link frenchcarforum.co.uk/forum/viewtopic.php?t=18082

I guess that with the cooling weather you may leave your aircon as it is for now.
When it’s cold enough, the regassers will arrive with ‘specials’ to keep themselves off the streets in winter.

Thanks for keeping us posted, it’s interesting, and my turn is coming soon too.

Regards,
Terry.

[dnsey]

Just noticed too, that the plastic above the aircon switch gets fairly warm when the aircon is on.
That must indicate that the current flows through the switch.

Yes, but if it's noticably warm, it suggests that the contacts have a high resistance (unless the warmth is coming from the pilot lamp in the switch, in which case it means nothing at all!).

[Clogzz]

Very good point, dnsey, thank you, hadn't thought of the lamp.
If the contacts are resistive, I guess that the switch will soon tell me, when the aircon won't work anymore.

[Mandrake]

Hi Simon,

Nice to read about progress.
It does look like the gas pressure is getting a bit marginal.
If it was outright low, then the low pressure contacts would prevent the compressor from starting.
Since it’s the normal pressure contacts that don’t always close, it must be an indication that the sensor switch is working normally.

Not necessarily. The switch contacts could be burnt or damaged, making it intermitant. But I agree, low gas is more likely.

On this previous photo of your engine bay, the sight glass on the dryer bottle has gone opaque, and so has mine.



That may indicate moisture in the system.

Hmm, according to the Haynes book of lies, (just going by memory, I don't have it in front of me) a blue colour means moisture, and it doesn't say anything about white... Anyway, whatever colour they said means moisture is not the colour mine is.

When all is normal, when you switch the air conditioning on, there should be a few small bubbles in the other sight glass at the top of the bottle.
Mine is constantly frothing brownish, but there’s still plenty of cold air coming in.

Well according to the book of lies, it should bubble a little bit initially and then within a minute it should be flowing continuously with no bubbles - which is exactly what mine does. It says that if it bubbles continuously it means the gas pressure is low, and mine doesn't do that, so this doesnt agree with the lack of activation of the pressure switch ??

I’ve only had one instance yet of the aircon not coming on, and switching it on a second time made it come good.
Just noticed too, that the plastic above the aircon switch gets fairly warm when the aircon is on.
That must indicate that the current flows through the switch.

Well on Dad's car the light in the switch has always barely lit up, and yesterday when we were checking it, the compressor and the light both wouldn't come on even though the bottle pressure switch was measuring ok.

I took out the 10 amp fuse under the dash which supposedly supplies the aircon control circuit, cleaned and refitted it, and presto, it started working again, (the compressor, not the cooling) although the light in the button is still very dim.

The strange thing is that the interior blowers and dashboard instruments both share that fuse as well (as evidenced by their stopping when the fuse is removed, and it also says so in the book) and yet they were still working ok Also the fuse in question is 10 amp, but I though the blower motors alone used 20 amps ???? Puzzled

One thing that worries me is that the aircon plugs face down, meaning that the regasser will have to access them from underneath.
Don’t know if they can be trusted to jack up a Citroën properly.
I'm thinking of normal height setting with the wheels hanging.

Yes it will require a bit of supervision with the suspension height, I had to do the same thing when I got new tyres - lift the suspension up for them etc...

Also seeing that on your picture, we can see the pavement under the car.
Isn’t there meant to be a plate under there ?

Thats actually a piece of old carpet on my garage floor to catch any oil drips... usually pavement isn't orange 8)

No, I don't believe there is a plate there, both of our 2 litre 8 valve petrol Xantia's don't have a cover there. Also the 1.9TD doesn't have a cover there either, although you can't see through there from the top because of all the piping...

I guess that with the cooling weather you may leave your aircon as it is for now.

When it’s cold enough, the regassers will arrive with ‘specials’ to keep themselves off the streets in winter.

Well the weather is cooling, but we still have a couple of months of potentially quite hot weather left.... although the average temperatures are dropping, the peak temperatures stay quite high for a while yet...

Regards,
Simon

[alan s]

If my answers are a bit vague at present, my apologies as I'm in the middle of some major mechanical jobs as well as house renovations so trying to scan through all the forums, particularly ones I moderate on is not a very exacting science at present.

As regards the sight glass and the colour. "Brownish" I don't like the sound of and you may have a dryer breaking down there but if it's going, let sleeping dogs lie.
With new gasses, it's not uncommon to get a few bubbles up to slight opaque due to the difference in the gas densities, so that's only a phenomena of 134a and again can be caused by other things too. Usually a colour in the sight glass is green due to some of the cowboy operators constantly dumping tracer dye into the systems and never tracing the leak. I'll swear some of them think it works like Barr's Leaks.
Another trap with the sight glass is that in a case where the sight glass is showing clear and the system is frosting back to the compressor, then that's usually a sign of too much gas and evaporator temps will be higher thereby not allowing the air coming off the coil to cool as efficiently as it should. It will also usually show itself in an over hot discharge line as well.
Another trap is that if the car is running and the compressor switched on, there's a sudden flash of bubbles through the sight glass and then it goes clear. For all intents and purposes, that shows it's all going as per normal, when in fact, it can be that there's practically no gas in the system and after the first flash of liquid, it then is pumped down and no gas in liquid form is passing therough the dight glass to give a reading so as a result, no bubbles can be seen.
These are some of the traps in trying to troubleshoot without gauges connected.
As regards access for re-gassing, just set the car on high ride when you leave it (not on the highest jacking position) and advise that the car will automatically rise for him when the engine is started. All they do is lie down at the front and slip under to fit the hose connection. If he's too much of a prima donna to get down on the floor to do the job, find a proper mechanic as the prima donna is obviously not only going to act like a bloody doctor, but will probably charge like one too!


Alan S

[Clogzz]

Hi Simon and Alan,

That’s quite a bit of matter to ponder over, with sight glass indications by themselves being inconclusive.
BoL says blue is normal, and high humidity is … red !
Even a 20 Amp fuse for the heater blower, and used for other things surprises me.
I have F20, 30 Amp, called “heater blower (power)”, and not doing anything else.
The only thing that’s properly cleared up is the orange garage floor.
Orange is not a likely colour for garage floors, though there are 'terracotta' and 'burnt orange' pavements, but I just didn’t think of a piece of carpet.
As per Alan’s advice, I’ll let the sleeping dog lie, but I’m prepared to shell out for a re-gas and new dryer bottle.

Regards,
Terry.

[fridgedoc]

Hi Mandrake & All

just to put my oar in..............

Cars using R134a ..... DO NOT rely on the sight-glass fitted to the drier you are liable to get some bubbles even when the system is FULL !!!!!

If the car is on R12 the sight-glass should be full "NO BUBBLES"

If the system is losing refrigerant it gets to a stage where the evaporation of the ref' in the evaporator is not getting to the TEV sensor at all the valve will open fully which will raise the suction pressure which in turn will raise the discharge pressure, depending on the "leak" this situation could last for weeks or months until sufficient refrigerant is lost and the system shuts down, this is the reason that the discharge pipe gets hotter than normal but it cools down by the time it gets to the condenser or even sooner!!!!! Normally the ref' goes through the condenser getting cooler then to the drier where it is still warm then on to the evaporator where the ref' should be liquid and as it goes through the TEV and is sprayed off into the evaporator and turns into a saturated vapour as it absorbs heat and then in to its gaseous state and depending on the system through an accumulator and back to the compressor to start its journey again.

This the reason you end up with weird and wonderful things happening, so all you need is a set of gauges and bottle of refrigerant to really
C**K it up......

And how many times have I seen just that, systems over charged, moisture in systems, wrong refrigerant etc.

Enough......... Enough.............

[alan s]

Methinks Haynsie either has a strip of that paper they used to use on cheap calenders years ago that changed colours when it was going to rain and somehow got it mixed up as to where he's seen it, has seen a different type of bottle on a receiver/dryer to any I ever had, saw the glass at the top and thought it sounded like a good idea at the time or has been drinking his own bathwater.
It actually would be a good idea, but that kind of thing could lead to all kinds of complications not only within the system but through owners doing self diagnosis. Some of the diagnosis I've seen come from even the guys working professionally has made my blood run cold at times and somehow I feel this might just ad to the already myriad of confusions, added to this of course is the cost factor and whilst prices seem to constantly rise, unfortunately quality rarely does these days particularly in the field of specialised and precision equipment so maybe it was something he saw many years ago.

Alan S

[Mandrake]

Hi fridgedoc,

I've had the car for 9 months now, and there has been no deterioration in the air conditioning that I've noticed - it had this "not always turning on" problem right from the time I got it until now, but its only now that I've learnt enough to prove that it is the pressure switch on the dryer stopping the compressor from coming on when it decides its not going to work.

Yes, I don't place much faith in the sight glass... it bubbles a little bit when it starts and then seems to run clear.

Could I still have a slow leak if it has remained almost the same for 9 months ? Or is it likely to be something else ? (Such as incorrect gassing by god knows who before I got it....)

Regards,
Simon