[Fury]

Hi Guys,  The air con unit in my FD used to be really cold, and last summer it started to fade, so it only functioned a couple of minutes before it retained the inside cabin temp.
Thinking it just needed a regas, I recently took it to an air-con guy, who diagnosed it. It still had plenty of gas in it ( I saw the gauges and saw the high and low-pressure sides in the "acceptable limits" area on his gauges. He also confirmed that the gas was within limits on his gauges.

He did further testing, with the engine running, the electronic clutch was kicking in, etc on the compressor, the high-pressure side getting hot ( as normal) the low-pressure side was NOT cold.

He diagnosed it as a faulty compressor    cost-plus here.
Car is an SR, with climate control, so checked out the basics of the modes, temp settings etc which seemed normal...

A new compressor and some considerable expense later, it is better but barely.  its been 40 degrees here in Aus recently and had the air pumping 34 degrees out of the vents!

Took it back and he topped off the gas and said to come back if the issue persisted - which it has - but wondering if anyone has any suggestions, please...

I have also cleaned out the pollen/cabin filter behind the glove box, the best temp I have got so far out of the vents, with a multimeter temperature probe is 7 degrees after 1/2 hr on the RHS outer dash vent, while 17 degrees on the left and 2 center vents after repairs and regassing.

The air con guy wasn't experienced with this model, being a 2009 Australian delivery, but it "used to" be freezing in all but the hottest days and very comfortable even on the hottest of days within a few minutes... so I really have no idea why it is so bad now - even with a brand new compressor.
I thought there may have been a climate control issue, letting hot air mix ( and haven't pulled the dash apart to investigate yey - and not wanting to either:head_butt:)
BTW: The low-pressure aluminum pipe is cool now but not freezing as it should be (IMHO)
The Hyundai dealer is also not familiar with this model as it is now 11 years old  their mechanics service them, but they really only do the newer models now.... really!   ah OOOOKKKKKK then...

I just want some feedback before I take it back to the air-con guy as he said he may need to start pulling it apart and on an hourly rate  - with no promises.
any thoughts or experiences are appreciated.
Cheers

[CraigB]

I’d be checking the thermal expansion valve.

[BrendanP]

I had my 2011 FD re-gassed, but the air-con became ineffective after a few days. Turned out to be a leaking condenser which was replaced under warranty. It should definitely be cold immediately after the expansion valve. If the compressor has been replaced then the expansion valve is the only other part of the system that I think could be faulty. The condenser and evaporator are passive heat exchangers so no moving parts to go wrong, unless they get blocked or start to leak.

What comes out of the evaporator (cooling coil) is a cool vapour. The compressor squeezes this vapour so it becomes a hot vapour, which is pumped through the condenser where it is cooled by the outside air flow. As it cools, the hot vapour turns into a warm liquid until it reaches the expansion valve, which is simple terms is just a tiny hole. As it is pushed through the hole, it turns back into a vapour (due to the low pressure) and the expansion results in a big drop in temperature, so it becomes a really cold vapour. This then extracts heat from the cabin as it passes through the evaporator until the cycle repeats as it returns to the compressor.

For all of this to work, the system has to be fully charged with refrigerant. Even if the compressor is pumping air around, the output will get hot because the air is being compressed, but because air remains a gas throughout and doesn't change states between liquid and vapour, you won't see significant cooling as it passes through the expansion valve. Assuming the system is fully charged, the expansion valve may be blocked so that the refrigerant can't pass through it even if the compressor is creating enough pressure drop though the system. It is also possible the compressor isn't creating enough pressure drop in the system so the refrigerant isn't turning back into a vapour as it passes through expansion valve.

If that's happening then it could be the compressor or the electronic clutch. The amount of effort the compressor does has to be controlled to ensure that under all conditions 1) the refrigerant has to have turned back to a liquid by the time it reaches the expansion valve and 2) the refrigerant has turned fully back into a vapour  by the time it returns to the compressor.

A competent air-con technician should work methodically and not waste time just trying different things at random to see what works. You shouldn't have to pay for hours of labour to find out it was a leak after all, when a leaking system is the very first thing they should check for. The approach I would take - armed with a basic understanding of how it is supposed to work - is to ask basic questions like 'are you 100% certain there are no leaks', 'does it definitely have the right amount of refrigerant', 'have you measured the system pressures and are they what you'd expect to see'

Ask them to explain what they're doing like you were a 12-year old. Unfortunately, I think some air-con technicians are trained how to use the machines to purge and re-fill air-con systems, but they don't fully understand how they works. They know what to do, but don't understand why they do it.

[Fury]

An excellent explanation of the process and some great points to raise. Thank you for your seriously in depth reply, it is really appreciated.

The previous system was very cold, the new compressor, very disappointing so far.

So, "IF" there is the required refrigerant still in the system, it sounds like either the Thermal Expansion Valve (TX valve) is blocked or malfunctioning, or the new compressor isn't pumping properly.
The high-pressure line is really hot, so it seems like there is at least some compression, but the low side is only cool - so from your explanation, it sounds like the TX valve is the likely cause.

At least I am now armed with information when I approach the service technician, so he doesn't just want approval to bill me for endless hours.   
 
Ill keep you updated, thanks again.

[The Gonz]

Engineer yet very much a visual person:

[Fury]

UPDATE:
Well, the Aircon guy was very thorough. Tested the system, after 2 weeks, the system had lost a lot of gas.

He checked for leaks, then did a high-pressure gas test, then also did a vacuum test. He also confirmed the TX valve was working correctly. He also didn't charge any extra for further diagnosis.
 
It turns out that the 11-year-old low-pressure lines were leaking.

The lines were degraded, but they are really expensive, so he suggested a technique, where the lines are resealed from the inside under pressure. Then regassed. A week on and it still seems fine.

Hopefully, it will be ok so I don't need to replace the low-pressure lines.
Thanks for the help.

[The Gonz]

That's very cool. I heard of that approach, like a self sealing tyre inflation. Good luck!

[BrendanP]

That's useful to know. When the dealer checked my car they used a dye in the refrigerant which showed up under UV light to spot leaks. That's great if it's somewhere accessible like the condenser, but much harder if it's in pipework buried away under the dashboard.

[Fury]

The Aircon guy did use the refrigerant with the UV green dye, but apparently, it only shows moderate leaks.  ( slow leaks can take days or weeks)  He found "traces" of dye, which made his search for leaks under higher "system" pressure more intensive, particularly in specific areas.

Initially, he was a little perplexed, because there were specs of dye on places that shouldn't be leaking, but after other testing, the connecting low-pressure pipes were degrading, which he said was quite rare and he was surprised by the result.