A bit of backstory for clarity (question below)

I've recently had my second A/C regas after realising that there must be a leak and so opted for a stop-leak and regas with dye to find out where the leak is.

After their really quick investigation of the problem, the garage has quoted me for a new condenser at £360 fitted.

I bought a UV torch to check this out myself, and the only place I can see a considerable amount of green dye is all around the A/C H service valve:

Green dye around A/C H valve

As far as I have seen online, the regas canister would be fitted to the L valve (please correct me if i'm wrong), and so any leak from fitting that would be around that valve surely? There is a small amount around that valve anyway:

Small amount of dye on the L service valve

For what it's worth, there is a tiny amount of dye on the cooling fan in front of the condenser, but not enough that I would think the leak is coming from down there:

Small amount of dye on the cooling fan


My main question is, is it likely that the valve is the issue here, given the amount of dye around it? And is it relatively straight forward for me to remove the blue H valve cover to see what's going on underneath, or should I just go back to the garage with this info...

2 Answers 2


Quite possibly the Schrader valves. They're cheap to replace but (in the US & UK anyway) it's illegal to vent R-134 to the atmosphere; it needs to be recovered correctly with the right equipment. You can remove the caps if you wish; if there's a little hiss, then that's another indication that the valve has gone. DO NOT remove the valve core itself.

Also check the condenser (usually in front of the radiator) for leaks using the UV light - if you see any evidence there (can be on the back as well as the front), then you definitely need a new condenser. You should also look for physical damage on the condenser; a couple of bent fins is OK, significant damage means a new one.

I'd take it to another garage for a second opinion, and show them these photos.

  • 2
    One could possibly check to ensure the Schrader valves themselves are tight ... might have become loose for some reason and be leaking. Jul 15, 2017 at 21:56
  • Thanks both. I think I'll leave it to someone that knows what they're doing. I had a hunch it may have been the Schrader valve, but didn't really have much info to give to a mechanic and didn't really want to mess with them. I appreciate the help! Jul 18, 2017 at 10:39

If it is the Schroeder, which happens more often than we would like, an AC service shop should have a tool for replacing one, which does not require the system to be discharged and recharged.

However, keep in mind that all valves will have some dye on them as a result of connecting and disconnecting the gauge hoses. If you wash the area, and see more dye accumulate, than you may have identified a core that is leaking.

For what it is worth, I always suspect the core, and they frequently leak. Care when connecting gauges can help a bit, but they are a low cost item.

You did not tell us what kind of vehicle it is, but I can tell you that there are whole families of cars in the US which have a history of evap leaks, which are inside the car's heater box, and where you would not observe UV dye. There are sniffers, which can help identify those leaks.

However, again, a good AC shop will have a sniffer, and a valve core replacement tool. While I have these, they are not common tools for DIY because of infrequent use.

  • 1
    Thanks - I thought there may be some leakage from connecting the hose, but not the amount that there is. It's good to know that it is a common problem. I've spoken to a mechanic who is going to take a look at the valves and advise. Jul 18, 2017 at 10:37

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