Any Air-con experts?

facade

Yet another fault with the Nissan-Renault Note.

After only about 2500 hours running the air-con has packed up. (It is never switched off)


It went from working to not working suddenly.
According to the pressure sensor output (via OBD) there was only about 20psi in the system, which is way below the vapour pressure of R134a, so there can be no liquid refrigerant left, and the clutch won't cut in.
Connecting a gauge to the low pressure port also reads approx 20psi.

So off for a re-gas, or at least a leak test and refill with leak tracer. (last re-gas was 3 years ago at Nissan)

Pressure tested ok, and passed the vacuum test for a refill, but they got over 50% of the refrigerant capacity out, and not a drop of oil :eek:

Re-gas and re-oil, and it seemed to sort of work, but not very cold got to about 8 degrees, at least the low pressure line was nicely covered in condensation..

Couple of days later, and back to warm air.
Quick look under the bonnet and the high pressure line felt cold, the low pressure was as hot as the engine.

Low system pressure again.

Waved the UV lamp all over the condenser and the lines, and round the pump, and not a trace of dye, except for drops at the fill ports.


So I need help with the diagnosis please.

If the expansion valve is blocked, (which I reckon would collect the oil at the blockage and account for the no oil recovered) could this somehow cause the static pressures to be so low?

Do you think evacuating the system for the re-gas dislodged the blockage enough to get it sort of working, and now it is blocked again?

Is there any point in getting just a new expansion valve, as the blockage can only be bits of compressor fallen off, and the new one will just block up?

Should a cheap (would it be a Denso from Telford, or an even cheaper French part?) compressor start breaking up after only a couple of thousand hours? (no oil would cause that, but I'm hoping that there was oil at the dealer service 3 years ago when it was re-gassed)


I suspect to fix it, it needs a new expansion valve, new compressor, new condenser (as there will be bits in it) and the evaporator and lines flushing out. That will cost more than the car is worth- or more precisely a lot more than the reduction in what it is worth when the air-con "just needs a re-gas" compared to working.

It just isn't worth spending hundreds on a professional diagnosis and new parts.

An expansion valve plus re-gas would be about £70, which is about £70 more than I really want to spend, the original re-gas was expensive enough at £30, and is as far as I'm prepared to go blindly.



If I had an air-con service unit, like most Americans seem to, I could just whip the refrigerant out and play around removing stuff to inspect it, but I have to work on a couple of external measurements and guesswork.:(

m_c

Low pressure is far more likely to be caused by lack of gas. Modern vehicles don't use that much gas, so it often doesn't take much of a leak for the system to cut out due to low pressure.

If UV die isn't showing up anywhere (it's often not that effective, but best results will be found in darkness, with a good UV lamp, and filtering glasses), I'd be looking at doing a pressure test with nitrogen gas.

As for the lack of oil, the fact whoever you got to regas it, 'reoiled' the system, tells me they're either not well trained, or like to BS.
Most modern systems will rarely draw any oil out during a regas, and adding extra oil can cause more problems than it'll solve. The only time oil should be added, is if you're replacing components that are supplied dry.


I'm not familiar with Notes, but it may not even have an expansion valve. Some vehicles just use a fixed orifice. Blockage of either would result in the compressor cutting in initially until the cut-out pressure was reached, then remaining there with very little cycling. Even if things were blocked to the extent zero gas was getting through, the high pressure would eventually leak back through the compressor over a few hours, as the valves in the compressor are not perfect (most are just a basic reed valve).

forgotmyname

Dodgy seal. The vacuum treatment pulls the seal into a position it wont normally be in because its never under a vacuum.

Pressurise it and it seals for a bit then fails again.

You cannot properly vacuum test a pressurised system.

facade

Thanks both.

It was pressure tested with nitrogen and held pressure for 20 minutes before the re-gas.

I don't have filter glasses, but I was using the UV lamp in the dark. If the refrigerant has all rushed out over a couple of days, I'd have expected to see a dye trace. I suppose it could be the evaporator core sprung a leak inside the car, but I didn't smell anything.

The expansion valve is fitted at the back of the engine compartment so you can change it (if you have the special arms with extra joints), which suggests they expect it to fail with monotonous regularity...

I just don't see why there is no static pressure, the sensor is on the liquid tank, so if there is any liquid in there it has to read the vapour pressure surely? (Which should be getting on for 60psi).

I only have a gauge that fits the low pressure port, but I'd expect the pressure to equalise when left standing, and it agreed with the pressure sensor output before, when it turned out to be 50% full.

A new pressure sensor is £30, but obviously needs emptying and re-gassing as well.

Initially I was prepared to invest £100 in a new condenser and a re-gas as I fully expected a stone hit to have pieced it and lost all the gas, but I can't find a leak.

I suppose it could hold so little refrigerant that 50% isn't enough to leave any liquid, so it could leak through a dodgy pump seal all the time there is a high enough pressure, and then when all the liquid is exhausted, the pressure drops and the leak diminishes to nothing.

A new compressor, if the seal is gone is £400.

Seems like I've no choice but to either pay for a professional diagnosis to minimise the parts spend, or just wear shorts and sandals (which is a lot cheaper) until I can find a half decent car to replace this one, but I was hoping to get 3 or 4 more years out of it.

BeenThroughItAll

I had similar symptoms when I bought my wife's Audi A4. It uses a 'choke' evaporator in an expansion pipe to the matrix rather than the more common evaporator in the matrix, and the blocked choke meant the AC didn't work properly (in fact, the wrong pipe was cold under the bonnet with it running - almost as if the cycle was reversed).


The pressure reading on VAG-COM was almost zero, so I simply removed the choke and fitted a new one - no gas escaped when I did, but when the system was subsequently recharged, more than 40% of the charge weight was recovered.

agrinnall

facade wrote: »

A new compressor, if the seal is gone is £400.

Bargain . I was told it would be around £600 for a compressor plus labour to change it on my Fiesta. I drove it with the aircon off for a few months then sold it to WBAC, who failed to test it - caveat emptor!

facade

BeenThroughItAll wrote: »

I had similar symptoms when I bought my wife's Audi A4. It uses a 'choke' evaporator in an expansion pipe to the matrix rather than the more common evaporator in the matrix, and the blocked choke meant the AC didn't work properly (in fact, the wrong pipe was cold under the bonnet with it running - almost as if the cycle was reversed).


The pressure reading on VAG-COM was almost zero, so I simply removed the choke and fitted a new one - no gas escaped when I did, but when the system was subsequently recharged, more than 40% of the charge weight was recovered.

It does sound similar...

The choke would be an orifice tube, as the Americans call it, that is just pushed into the line to the evaporator at a gland nut where the high pressure line changes diameter. (A thin pipe stuck through a bung with o-rings on, covered in a mesh filter, there are loads of American videos on fixing your air-con, they all seem to have the gassing kit in their garage though)

Mine has an expansion valve definitely.


Maybe the expansion valve is virtually blocked, and whilst there was gas in it, it continually over-pressured and cut out, forcing refrigerant out of a seal somewhere.

The dodgy "eco" system on the Note (I think just dodgy full stop) is designed to clonk the compressor clutch in & out all the time, so you never know if it is short cycling- which would indicate loss of gas or over pressuring.

m_c

It depends on where a leak is. For the UV dye to be visible, it's relying on some oil leaking out along with the gas to carry the dye. If it's just gas leaking, the UV dye and oil will remain in the system.
There is no ideal system for diagnosing aircon leaks, as it depends on where and how big the leak is, as to how easy or hard it is to find.


It could be something that only leaks when driven. I've seen holes in pipes/condensors caused by chaffing against something, and they only noticeably leak when moved, yet can hold enough gas for a few days to remain working. However, with UV dye, you'd normally see a slight trail from the leak. If the leak is not directly visible, you probably won't see the dye.

BeenThroughItAll

facade wrote: »

It does sound similar...

The choke would be an orifice tube, as the Americans call it, that is just pushed into the line to the evaporator at a gland nut where the high pressure line changes diameter. (A thin pipe stuck through a bung with o-rings on, covered in a mesh filter, there are loads of American videos on fixing your air-con, they all seem to have the gassing kit in their garage though)

Mine has an expansion valve definitely.


Maybe the expansion valve is virtually blocked, and whilst there was gas in it, it continually over-pressured and cut out, forcing refrigerant out of a seal somewhere.

The dodgy "eco" system on the Note (I think just dodgy full stop) is designed to clonk the compressor clutch in & out all the time, so you never know if it is short cycling- which would indicate loss of gas or over pressuring.

Exactly that, the orifice tube is the proper description - Audi list it as 'choke' but you're correct that's not what it's really called.


No idea if you'd see the same with a blocked expansion valve. It's doing the same basic job, so perhaps...

facade

So I'm down to

taking a punt at the expansion valve (and as I don't have the special arms, take the inlet manifold off to get at it- might as well do the sparking plugs for another £40 at the same time)

it is broken, so the windows mist up all the time that it isn't 50 degrees inside the car.....

pay someone to diagnose it properly. I doubt if anyone will diagnose the leak for less than £50 if it needs a sniffer and more gas to find it though, and then I still have to change something expensive.

iolanthe07

A new compressor, if the seal is gone is £400.

You're lucky. A new compressor for my MX5 is £675, and is made only by Mazda for my particular model. Apparently compressors are liable to be punctured by stone chippings as they are fixed low down. I'm not sure whether I shall bother, but motorway driving with the roof down is not great.