Fault finding A/C system.

I thought I'd share the fault finding of my air condition system as it had stopped working.
So when I press the A/C button on the A/C control...nothing. All the other controls work and if I Use the LEXIA I can get the compressor clutch to pull in. This can only be done while the engine has stopped.
If I can get the clutch to pull in then it's not the electrical side.
The next usual suspect is the gas, or more specifically the loss of gas. The engine ECU wont allow the compressor clutch to be pulled in if there is no gas.
There are two access ports on the refrigerant lines of the system. One High pressure port and one low pressure port. When the system is running of course the pressure in the high side is high (about 100-150 psi) and it's low on the low side (about 10-20 psi). If the aircon has not been running for a while the pressures equalize on both sides to about 40psi.
Hooking up the service connectors.

So if there is gas in the system it should be at about 40psi.
Well there's your problem! Hmm, no gas. Not that surprised.
Attach a vacuum pump and 'vac' the system down to zero psia(-30psi on the gauge). This is to get rid of air and moisture in the system and is also a test to see if there are leaks in the system. It's not foolproof as we are about to find out. At this point I added 3mls of florescent dye to the system to help spot leaks.
I vac it down for about half an hour and stop the vac pump. After another half an hour the gauges still show -30psi. Well, it's not a big leak.
I disconnect the Vac pump and connect the refrigerant to the service line. Next, start the car and turn on the A/C. Of course the compressor wont kick in yet. I slowly add refrigerant to the system until the compressor cuts in. At 30 psi the compressor cuts in! Now, I don't want to waste refrigerant because I know there is a leak, just enough to get the system running, not a full charge. It's not running well but that's OK there is not much refrigerant in the system. I shut down the engine, disconnect every thing and have a look around. I'm looking for oil leaks (there is a small amount of oil in the system to lubricate the compressor) and my UV dye. Also listening for hissing as the gas escapes.
The high side schrader valve is leaking, I can hear it hissing. Could be it hasn't sealed properly so I push on the valve to see if it reseats. The hissing dies down but doesn't stop. Could this be my leak? The low side appears to have a small leak too.
I decide to remove both valves and replace them. Of course I loose all the refrigerant in doing so. That's why I didn't put in a full charge.
Hmm not the best examples I have ever seen. So I replaced them with ones I prepared earlier.

I go through the process of vac'ing the system down and adding refrigerant. This time no leaks...that I can spot. Now it's a waiting game. See if it stays sealed up or, if not, see if I can spot the leak from the UV dye.

Did you see any sign of dye on the valves? I have a problem with my C4 Grande Picasso, where a charge will just about last a summer, but is empty by the spring. Citroen have put double doses of the dye in and inspected it several times, but they cannot find evidence of a leak, but the fluid has gone! It's a pain but isn't costing me money as the car is under warranty.

My wife's Renault has a similar issue, the A/C needs charging annually, it works for the summer but by the following year it works but only just. I'm going to try some 'leak stopper', it's supposed to help with leaks on seals. As the gas takes the best part of a year to escape and there are no discernible leaks I'm thinking it's maybe a seal in the compressor.

It might be a while before I know, ie next spring but I'm going to try. If the worst comes to the worst and I have to re-gas next year at least I will have the pipe, connections, valves etc to use a DIY re-gas cannister with.

Routmaster1, do you mean: was there dye present before I started? No but the problem with second hand cars is you don't know their history. So I have no proof there is or isn't 'anything' in the system, let alone dye.
Thank you for reminding me that I was being sloppy. I didn't flush the excess dye from the port. I added the dye to the port by using a syringe and 'sucking' it into the system under a vacuum, leaving residue on the port threads. So I (just then) flushed the port with isopropal alcohol and left some alcohol floating above the schrader valve-no bubbles!
If you have been following my...er...adventures, you would know I had refrigerant loss on the 'other' C3 that I fixed up. That one had lost refrigerant because one of the lines had rubbed on the engine mount and caused a hole. The refrigerant literally leaked out over night BUT no signs of oil leaking from the hole!!! Oil circulates around the ENTIRE system while it's working. Most remains in the compressor, where it's supposed to be but some vaporizes and is carried around the system with the refrigerant. If there is a hole, the oil goes out with the refrigerant. So how did no oil come out with the refrigerant on an over night leak, not even a tiny amount? Oil loss? Add some oil? The problem with that is that the oil displaces refrigerant and too much oil will reduce the efficiency of the system. The only way to add oil properly is to flush out any residual oil and fill the system with the manufacturers recommended quantity. That requires removal of the compressor (which is drained separately) and the receiver/dryer! It also requires a special machine to flush the system. A very expensive exercise. So the cheap way to add oil is; not do it in the first place...or guess. Which one are you going to do?

Unfortunately the quality of technicians varies and some do a good job and some don't. That's partly why I do most of my own servicing. I have seen technicians with the most advanced equipment available and still unable to do a good job. How often have you been unsatisfied with a wheel alignment?
A long story short - I paid good dollars for an auto electrician to fault find my A/C system (in another car) and they couldn't find the leak. I went over the system and found oil 9!$$ing out of the compressor's front seal and a massive build up of dye. They couldn't bother to get under the car? At the time I hadn't done much with A/C systems (which is why I went to a professional) but I quickly learnt how to repair and service them and do it properly (well, better than them).

I got a UV light from Ebay for inspection, it was quite cheap. You might get one yourself and see if you can do a better job than them.

See, your Grand Picasso is new and you know the history but still no oil coming out of the system with the leak! So the answer to your questions is...I don't know why these cars can leak refrigerant and not leave some trace behind. As Mr Spock would say "logic would dictate there is no oil in the system as it does not leak out" but you have a brand new car and logic says there is no oil in the A/C system????? I find that very hard to believe...so I have no idea what is going on. Are they using a very heavy weight oil that doesn't circulate around the system and stays in the compressor? The oil in an A/C system has to have some very special properties to be compatible with R134a and to my knowledge there are only 2 types of oil that are suitable (PAG and POA) and they circulate around the system. Is PSA using a 'different' oil? I cant answer that, I don't know.

R134a can leak through the pores of (some) flexible hoses BUT that rate is about 10% of the refrigerant in 10 years!

There was no oil (or dye) leak from the schrader valves in the C3 I am currently working on because the system had not worked for more than a year and all of the oil would have pooled to the lower parts of the system. It wouldn't have started to leak oil with the refrigerant until I got the system running and the oil circulating. So it was just leaking refrigerant at the time. Well that's my theory.

If you are asking me "can the refrigerant leak out of the schrader valves of my car too?" I say YES! The quality of the rubber seals in these valves is quite poor (have a look again at the pictures of the valves). The dust caps can also slow down the leakage rate. The valves I got from China ware actually a better quality than those that were installed. However, I have no proof that those valves installed in my car were OEM but I doubt that they were ever replaced.

Missing Lincs wrote: ↑Sun Jun 14, 2020 11:53 am maybe a seal in the compressor.

Most of the oil in the system is in the compressor . If the compressor has a leak of any sort you will definitely see oil coming out (if there is oil in the system).

You can try a 'home brew' of water and dish washing liquid in a squirt bottle and spray it all over the parts of the A/C system. Including into the schrader valves. Unfortunately at the rate you are talking the bubbles produced will be very small.
An R134a leak detector 'sniffer' would find a leak but that requires a trained technician. If not performed correctly the test will fail to find a leak.

Anyone know whether Citroen or other manufacturers put dye in the system from new?