i have for my sins a 2009 Hyundai, great little shopping trolley, when i bought it 4 years ago, the air con didnt work, had it re-gassed, worked for a couple of weeks then didnt go cold again, took it back, no probs found, another re-gas and away you go, same thing happened.
summer had ended so for got about it, had it re gassed the following year, told them about the previous probs, put dye in, couldnt find a leak, same thing happened again.
twice was at a main dealer and twice at kwikfit with same result, is there anything i can check, pressure valve giving low pressure signal etc ?...summer is coming soon and a farmer tells me it,s going to be a hot one.

I would check for a leak with a UV lamp in the engine bay as well as around the dash area. Bet they didn’t check the dash cos
“ You can’t get thicker than a #####fit fitter” Sounds very much like its loosing gas, try checking the service ports with the caps off

[Edited on 6/4/19 by rusty nuts]

No visual leaks, sounds like the evaporator inside the heating box, you need someone with a sniffer to detect r134 coming out the vents.

they did the thing with "disco glases" and some sort of a torch, i was supprised at how much effort quickfit took to find a leak, under the dash and the bonnet, if i put a tyre pressure gauge on the ports, what sort of pressure am i looking for ?

When a very thorough independent AC man came and looked at the porsche, before any re-gas he did a pressure holding test with nitrogen? first and left that for at least 15 mins then did the same with the system under vacuum also for about 15 mins. There are some very expensive Porsche pipes that are known to fail, so a wanted to be 100% if there was a problem that we got it right.
After an hours testing couldn't fault it, as it happens, so was happy to re-gas/oil and dye. Save for a noisy a/c pump clutch.
Anyway ISTR it might have been abiout 40psi?

There is an unlimited fine for knowingly discharging r134a into the atmosphere, hence the pro using nitrogen to test a potentially leaky system.
The dye is intended for long term fault tracing, not to find leaks in the first place.
There is also nitrogen with hydrogen trace to allow use of a sniffer device to find minor leaks.

Your leak is likely condenser damage or o-ring sealing affected by corrosion at the joints, if dye has previously been injected, there should be a yellow glow under uv light at any point of leakage - this may have washed away in the time since the a/c was last working.
If you can't see anything, an a/c specialist is your best bet, as mentioned alot of garages/fast fits have the equipment and no-one with the knowledge.

Dave

thanks for the replies peeps, as i said, twice i went to the main dealer but suspect they are about the same as titfit, put the machine on and let it run it,s cycle, they did the vacume test as i was waiting there.
i cant find an AC specialist and dont have the gear so have to leave it to the local bods.