Technical A/C troubleshooting

[Jillos]

Appreciate this can be a pain to troubleshoot as could be so many things, but looking for some simple things to try first.
Fiat 500, 2012, air con not blowing cold, compressor not kicking in.
Radiator fan kicks in when car warm, so that’s not dead.
Obvious thing would be to re gas, but that would be too simple, surely?!
Any other bits and bobs I can try, or suggestions?
Thanks.

 

[PuntoHowTo]

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Obvious thing would be to re gas, but that would be too simple, surely?!
Any other bits and bobs I can try, or suggestions?
Thanks.

Lack of gas is 99.99999999% of the time going to be the cause.

The issue will be, why there is no gas. It’s probable on a 2012 that it has a leak somewhere, most common culprit is the condenser, which as they age can corrode and then leak.

I’m not saying that is 100% definitely the cause but I’d probably say it is the most likely cause.

Unless you have a machine to refil the system with gas, it’s going to be difficult to fault find.

If the system was working but it was just very weak, then I’d suggest one of the numerous diy recharge kits you can buy, but I wouldn’t advise that if the system is not working and you can’t be sure there isn’t a significant leak somewhere.

 

[Mike1alike]

Obvious thing would be to re gas, but that would be too simple, surely?!
Any other bits and bobs I can try, or suggestions?

First thing is gas, yes. And if you have a diagnose tool and MultiECUScan you can hook up and read the system's pressure. If gas is in and compressor not pumping for some time, normal system pressure is about 6-8 bar on full gas. If you read around ~1 bar, that would be the atmospheric pressure so system has no gas in.
But means the presostat is working, which is the second thing for your problem. Faulty presostat doesn't give ECU the pressure reading and compressor doesn't kick in in that situation because ECU doesn't give it the start command. So if you can't read the pressure with the diagnose means presostat is bad.

Gas is not quite that simple, because usually it leaks out of the system. So filling gas is simple, but keeping it in can turn to be difficult sometimes. Most of the times it's lost on very small leaking points and if you fill up AC will work for 1 year, 2 the most, then needs refilling again. If there's a big crack in the system you would find it immediately while trying to refill. People doing the refill would find it actually, because they would be able to make the vacuum inside, which needs to be done before refilling.
If there are small leaks you can usually spot them after refill, with UV light and glasses if they put in the substance to see, along with refrigerant gas. The usual minor leaking points are worn out orings on the system or one that is almost always ignored, the worn out service valves caps seals.
This is good quality and not expensive service valve cap size M8 that usually fits on most Fiat AC systems, AC Service Valve Cap-Thermotec KTT500012, but if you need one best check before the size on yours.
Being 2012 year, if you have the car's service history and know those weren't replaced and if they find small leaks on vacuum test, I would say it would be the best to replace the service valves caps and the orings on the system before refilling. Orings sit where pipes are connected to system parts, to compressor, to condenser and to expension valve and also, the presostat has one oring too.

 

[Jillos]

Thanks so much both, really helpful. There’s a couple of other bits I need to look at first (auction buy a couple of weeks ago) but will come back to this.

 

[John202020]

The condenser is known to give up, causing a leak, if you get it sorted remember to never turn off the AC

 

[The Panda Nut]

The condenser is known to give up, causing a leak, if you get it sorted remember to never turn off the AC

Yes I agree. Have a look and you can see if the codenser is disintegrating. Low gas causes Air con shutdown. Small leaks not condeser related can be fixed sometimes with an additive.

 

[PuntoHowTo]

First thing is gas, yes. And if you have a diagnose tool and MultiECUScan you can hook up and read the system's pressure. If gas is in and compressor not pumping for some time, normal system pressure is about 6-8 bar on full gas. If you read around ~1 bar, that would be the atmospheric pressure so system has no gas in.
But means the presostat is working, which is the second thing for your problem. Faulty presostat doesn't give ECU the pressure reading and compressor doesn't kick in in that situation because ECU doesn't give it the start command. So if you can't read the pressure with the diagnose means presostat is bad.

I’m going to have to disagree with this to some extent.

The pressure of the gas Is proportionate to the temperature of the gad and if there is any liquid in the system.

So half your gas could leak out but you would still get 6bar at 21°c.

Also if the temp goes up or down that can also massively affect the pressure inside the system.as long as there is liquified gas then it will maintain that level of pressure/temp.

So 6-8bar is fine for now as it’s when the outside temp is 6-8bar or 21-32°C but the temp level may differ in cold or extra hot weather and the normal level gives a different t to that

 

[Mike1alike]

*Correction: I wrote about service valve cap. But, as picture of the part shows it, I meant the service valve core there.

I’m going to have to disagree with this to some extent.

Well... you're not wrong.
But... If there is a small leak, on worn out orings or service valve cores, it's exactly the pressure inside the system that's making the refrigerant gas leak. If at any point there is 6 - 8 bar pressure, it's seen as "ok" and compressor will start when AC is turned on. And it will increase system's pressure and make more refrigerant to leak out. Compressor does start on lower than half gas level in the system. I had mine running on less than 20%, was 90 g out of 550 g. AC would still put out some cold air, but well under its full capacity. When gas is lower and system still works, there is a distinctive telling sign. The expansion valve whistles, squeaks. So there will be that noise under the dashboard because pressure is lower than normal due to lower gas and that can't fully open the expansion valve, only partially and gas squeezes through to evaporator. So that noise is a big tell.

So if you're saying @Jillos's system is not having a smaller worn out orings/valve cores leak you are probably right, it is very likely the condenser.
But... they are not exclusive. It's not just one or another. I just tried to underline that for a healthy system it's very wise to put new valve cores and possibly new orings after more than 12 years of use. Otherwise you would need to refill gas every year.
Also, AC system working and being turned on during cold season too it's what keeps the orings and valve cores in good condition. Because there's oil inside that moves along with gas and keeps them hydrated. Otherwise they dry out and start leaking.
So putting just a new condenser on after longer time out of service may have the system working perfect at first but surely that will start leaking gas in short time.

Condenser has the dehydrator filter and that needs replacing sometimes, after years in service. Filter getting filled leads to condenser failure, little humidity inside making corrosions on condenser. Also, many times filter brakes and filtering core inside is spread through the system and that blocks small passages, mostly the expansion valve.
Some systems have the dehydrator filter as separate part and filter there can be replaced alone, others have it as one part, condenser + filter and that needs to be replaced when it calls it.

 

[Jillos]

I have ECU scan capability - will be running it today (if it doesn’t melt!) to recheck camshaft sensor fault before I (attempt to) fix it, so will look at ac diag as well.

 

[PuntoHowTo]

If at any point there is 6 - 8 bar pressure, it's seen as "ok" and compressor will start when AC is turned on.

In the weather we are having in the uk right now the gas pressure should be between 8-9bar static gas pressure.

If it is reading less than that it is a pretty good indication that the system is running low on gas.

In hot weather it can seem that there is too much gas with very high pressures. When it gets very cold ie in the winter the temperature is reaching 0°c then it can seem that there isn’t any gas.

There is little point worrying about the pressure because as I said it sits at a pressure directly proportional to the ambient temp.


So at 6bar 20ish°c there could be loads of gas in the system and the excess gas will turn into a liquid. Or the gas has leaked out, there is virtually no liquid gas but there is just enough gas to keep the pressure at 6 bar.

If you have a situation where there is very little gas available to turn into liquid, then there is no spare capacity in the system. When you turn on the ac the hot side pressure builds but the low Sid pressure drops too low and the system/compressor will keep cycling on and off.everh few seconds just to try and keep some pressure in the low side.

So technically speaking the only way you access the quantity of gas is to recharge the system with the correct weight of gas.

The pressure will tell you if the system should turn on and off but realistically if the weather is cold the pressure can be low enough to make it seem like there is not enough gas if you only look at the pressure readings.


That’s why ac gas is measured by weight not pressure

 

[Mike1alike]

...

All that is of no relevance to @Jillos's problem. At his it's important to read the pressure now to know in the first place if the presostat is working. If presostat is bad it gives no pressure reading and then compressor doesn't start because it is not given the start command by ECU.
If pressure is shown, it will be telling. We consider the atmospheric temperature that is now and if the system pressure is about the same as atmospheric pressure means there is a big crack somewhere on the system that let all the refrigerant gas out. It would never be 6 bar in a system drained of gas with compressor not running for a while, it would be about 2-3 bar at most, but that's not happening now because compressor would kick in at that pressure.

 

[Jillos]

Hi, so I've run the diag on the AC but it seems to be limited. You can turn the compressor relay ON (which I did and it clicked and said ON), but the AC request is off, even when fan and AC button on.

@Mike1alike do you suggest I buy a regas kit with the pressure thingy first, then I can check if there IS any pressure is in the system, then take it from there?

 

[PuntoHowTo]

Ok to clarify why what I am saying is relevant.

You can have above 6bar of pressure read on MES but there not be enough gas in the system for it to work properly.

To prove what I am saying this video shows a car with between 6-8bar of pressure as read on MES but it was not enough gas for the AC to actually work

Hi, so I've run the diag on the AC but it seems to be limited. You can turn the compressor relay ON (which I did and it clicked and said ON), but the AC request is off, even when fan and AC button on.

@Mike1alike do you suggest I buy a regas kit with the pressure thingy first, then I can check if there IS any pressure is in the system, then take it from there?

See the video above it shows on mes the pressure readings that @Mike1alike is talking about, but as I said above you can have between 6-8bar of pressure and the sustem still not work.
@Jillos, don’t buy a regas kit,
Run your test again turn on the ac compressor relay and with the bonnet open and the engine running, look to see if the centre of the AC compressor pulley is turning with the engine.
You can look on MES at the system pressure but it may not be relevant.

If the compressor is not turning then the best thing you can do is take it to someone to have it regassed properly, and more importantly leak tested.

A ac regas kit is often more expensive than just booking the car in for a regas, but if there is a leak the cost of the regas kit will be lost to the atmosphere, if there is a leak and a proper AC regas is done they will tell you and they won’t recharge the system with a gas leak potentially saving you a huge chuck of money.

The only time you buy a regas kit is when the sustem is working, it’s just weak at cooling the air.

 

[Mike1alike]

Ok to clarify why what I am saying is relevant.

You can have above 6bar of pressure read on MES but there not be enough gas in the system for it to work properly.

No, I know that. There was no need to clarify it.
Just in the case in this topic the compressor doesn't start at all. That is different than your situation in the video, there compressor would run, just couldn't put out much cold air, not having enough gas in the system. Which by the way is very bad scenario to run it like that because gas is mixed with oil and does the compressor lubrication and if you run it low on gas chances are lubrication is not done as it should and that damages the compressor in not very long time.

 

[jrkitching]

The issue will be, why there is no gas. It’s probable on a 2012 that it has a leak somewhere, most common culprit is the condenser, which as they age can corrode and then leak.

Basically that.

I'd start by visually checking the condenser; it's the first thing you see when you look through the front grille. On a 14 yr old 500, I'd be astounded if it's still got many fins left; with the amount of salty roadspray that gets thrown through the grille in a UK winter, they are a very common point of failure. They'll still work without the fins until you get a leak in one of the cooling pipes, but that's just a question of a bit more salt spray and time. I wouldn't bother doing anything else unless the condenser looks to be sound and has most of its fins intact.

Aftermarket condensers are cheap enough, and if there's no gas left in the system you could just replace it yourself. Before trying to regas it, I'd recommend vacuuming the system to remove residual moisture and testing it to ensure it's gastight. This isn't really something you can do yourself with a cheap canister kit; I'd take it to a reputable A/C specialist for this. If the system won't hold pressure, they shouldn't charge you the full regassing fee and you can make an informed decision on whether the likely cost of repair is worth it on a car that's as old as this.

If it's been left in an unserviceable state for a significant period without gas, the compressor may be toast. In that case, I'd just live without A/C.

 

[Mike1alike]

Hi, so I've run the diag on the AC but it seems to be limited. You can turn the compressor relay ON (which I did and it clicked and said ON), but the AC request is off, even when fan and AC button on.

@Mike1alike do you suggest I buy a regas kit with the pressure thingy first, then I can check if there IS any pressure is in the system, then take it from there?

What software are you using to connect to ECU?
Sounds like you entered the 'Actuators' section. AC system pressure can be read in the 'Parameters' section if you can read it. Unfortunately, some models don't show it.
There is no use to buy a regas kit. I don't know what pressure thingy there is on a pressure kit. But you do need to read the pressure first and most important, ECU does too. If it doesn't read it, it keeps the AC request off and if presostat is faulty system can have gas and not need refilling.
Was the engine running when you did that?

 

[Mike1alike]

And yes, I too recommend this to be done at a reputable AC specialist garage because there are too many specific details that can't be done without the tools they have. You do need to put system under vacuum and test if compressor is working, mend the leaking points if there are any otherwise you'd fill it for nothing, all the gas you fill gets lost in no time.