tommyaudi

My AC stopped working after the winter so I took a chance and replaced the pressure switch as it often gives up and is cheap anyway. + is too much of a rookie to troubleshoot an AC. Also live very deserted and very far from workshops.

But: when I changed the pressure switch, it was gas that came out, so I quickly screwed on the new one. However, the AC still does not work and now the fan runs unusually often instead. And the ac button cannot be pressed now. However, it has been very cold so maybe that is why?

After some research it seems that the valve under the pressure switch should make 0 gas come out when you unscrew it? So it seems broken? Can I change it myself without having to top up the gas at a workshop afterwards? Is the gas dangerous to breathe?

1. Should there be 0 gas when you change the pressure switch?
2. Can I change the valve underneath without having to top up gas at a workshop afterwards? (+ what kind of valve is that? Can someone link?)
3. Is the gas dangerous to breathe? How do you do it in a workshop? Do you use a gas mask then or not?
4. Is it the case that it is not possible to start the ac under a certain temp outside?

The car is a 2017 Audi A4 but is the same on many Audis (and other cars) I guess. The car has done about 13,000 miles. (that's why I thought I can change the pressure switch regardless so it's fresh.)

Wish you a nice weekend!

tommyaudi

Ok after some searching I realize I have to take it in to to a workshop to replace the valve. But still interested in answers to questions out of curiosity and learning.

EDIT: Could it be bad to continue driving if the valve between the pressure switch does not work?

SMac770

The refrigerant pressure switch valve is a normal Schrader valve design, afaik. If you need to replace the valve, it's 8A0820855AA. But you're going to have to evac the refrigerant properly first, and the reload the circuit with the correct weight of refrigerant and oil after. Just venting refrigerant into the air should be illegal, and is certainly not something you should be breathing. You really should let a shop process this issue; you do not have the knowledge or tools to do the task correctly.

The basic car operation doesn't care about the refrigerant level. It will realize something is wrong with the refrigerant circuit and not let you engage the AC function (you can always press the button, it can't be physically locked out, but the system can ignore that button press). But beyond that, the car will operate perfectly fine.

tommyaudi

Thank you very much for a good and clear answer.

Yes you are right, I will contact a shop as I can't handle this unfortunately. Changing the pressure switch was as far as my knowledge went, and then it ended

But good to have what you wrote when I'm contacting a workshop. (And interesting to learn) Since the valve continued to leak when the pressure switch was off, should it be the valve that the workshop should replace?

Good, then I can keep driving the car then. Although it feels strange that the fan runs so often.

Is the gas so dangerous that what leaked out when I changed the pressure switch was dangerous for me?

SMac770

I don't know if your MY17 would use R134a or R1234yf for the refrigerant. It's probably on a sticker somewhere in the car. From the workshop manual on R134a, it seems like the main concerns for exposure are more about the cold and degreasing, to wash with lots of water exposed areas. The toxic concern seems more related to decomposed refrigerant. "A burning cigarette can cause refrigerant to decompose. The resultant substances are toxic and must not be inhaled." Still, when a global industry that knows they have to change a substance due to exposed (to public knowledge) threat to people and environment, they're going to undersell any issues with it.

Yeah, a valve is a valve, it shouldn't be leaking. So I assume it should be replaced. Hopefully the issue is the valve and not the valve seat, which is part of the radiator.

If the A/C is not running, the fans should only turn on when the coolant goes over 120°C or something like that. You'd have to review the measuring values for the coolant temp and fan duty cycle to determine if fan operation is inline with the ECM control, or if you have other issues going on.

tommyaudi

Thanks for the reply!

It seems to be R1234yf because I have received a reply from a workshop already that they do not work with "the new gas". Awaiting responses from two more. So now I wonder even more how dangerous it might have been when it leaked when I replaced the switch. I was standing outside the garage when I changed it, so it might have been a little better.

The strange thing about the fan is that it started to run a little now and then after changing the switch. Only runs for a second or so and stops and then a second or so again. And not all the time but in a strange pattern. And right from the start, when the car has been standing for a day.

SMac770

At that point, I'd see what comes up in a VCDS scan and work the actual errors present. But you might as well start with addressing the already known issues, then see what remains.

MichaelCarter

The valve you're talking about is probably the Schrader valve, which is like the valve on a bike tire. It shouldn't let gas out when you take off the pressure switch, so if it's not sealing right, that might be your problem. To replace it, you'd usually have to drain all the refrigerant from the system first. You can't really do that without special equipment and some know-how, so it's best to leave it to someone trained in this kind of work.

tommyaudi

Thanks for the reply!

Then I hope to get an answer from a workshop that can help me change it this week. Let's see if it also solves the problem with the fan.