Automotive Air Conditioning Information Forum

JohnHere wrote: Sat Sep 05, 2026 11:27 am IMHO, the advice Cusser posted is 100-percent correct.

If you have the knowledge, skills, and tools to work on the system yourself, I suggest concentrating on potential leakage points first. Leaks could be anywhere, but I would focus my attention on the condenser, the compressor shaft seal, the area around the control valve, the compressor's belly, the condensate coming from the evaporator, and every joint to which you have access.

If you're located in the Rust Belt, I recommend closely examining any metal lines routed down low, as well as the bottom of the condenser, for pinholes.

I would also examine with a magnifying glass the service ports themselves and the areas in which they're welded onto the tubes. If you need replacement tube assemblies, they're available at reasonable prices. Check with Tim at ACKITS.com, this Forum's sponsor.

Nylog Blue is an excellent product and is compatible with all MVAC systems and components. I wouldn't use any other substances that might contaminate the A/C system.

Agreed.
Thanks for the Nylog Blue suggestion. I had not heard of it and ordered some for my use.

I use Nylog Blue on every o-ring, gasket, and threaded connection, including Schrader valves and valve caps.

The caps are indeed what forms the final bubble-tight seal, not the Schrader valves. Carefully examine your existing caps to ensure that the sealing rings are in place and intact (they're located deep inside the caps), and that the threads aren't stripped. Replace them if necessary.

Metal caps are available in the market. They look nice, but they're more expensive than the OE plastic variety. The choice is yours.

Some comments about UV dye: It's okay to use, as long as you don't use too much. One-quarter of a fluid ounce is fine. Much more than that risks diluting the oil, which might reduce the oil's lubricity and its ability to lubricate the compressor.

I'm unsure whether the Calgary Roads Department uses chemicals to melt ice and snow during the winter months. If so, pay particular attention to metal A/C lines routed down low, and the bottom of the condenser, as already mentioned.

As for instructions to the shop, I would concentrate on the leakage points previously discussed.

I will not post Amazon or auction links because they don't support us; people seeking free advice never do. Brass caps have been and still are the best service caps available.

Tim wrote: Mon Sep 07, 2026 11:40 am I will not post Amazon or auction links because they don't support us; people seeking free advice never do. Brass caps have been and still are the best service caps available.

Is there a risk that a brass cap could strip the threads out of an aluminum service port?
On my VW GTI the service port and the A/C lines are all aluminum. The caps are plastic. I'm thinking that perhaps VW uses plastic caps to prevent damage to the aluminum threads. So if somebody overtightens the cap, the threads on the cap will strip first.

Never had a problem. If the individual is wrenching a service cap down hard enough to strip the threads. They should not be working on the vehicle. New valve core and Brass cap, best option out there.

jfklein wrote: Mon Sep 07, 2026 1:05 pm I'm thinking that perhaps VW uses plastic caps to prevent damage to the aluminum threads.

No, it's that plastic caps are cheaper.

jfklein wrote: Mon Sep 07, 2026 1:05 pm So if somebody overtightens the cap, the threads on the cap will strip first.

The caps have an internal rubber seal. Only an idiot would crank those super-tight.

I took the below photos of the rims of the high and low side service ports in my VW GTI. I used my iPhone so the photo quality isn’t the greatest. However they show some nicks and dents on the rim. I'm thinking that perhaps these are preventing the o-ring in the cap from sealing properly.

If this is true, I’m not exactly sure how this would be fixed. Maybe sanding the nicks and dents down with emory paper would work. But it’s difficult to sand a rounded surface like these rims. So maybe sanding a flat surface around the top of the rim using a sanding block with the emory paper would work. This would give the o-ring a flat smooth surface to seal against. But the surface would also have to be level. So it could be difficult to do.

Another possibility might be to put Nylog Blue on the rim or the o-ring. Maybe it would fill in any nicks and dents and allow the o-ring to seal.

Another possibility might be to use the FreezeCap or A/C QuickCap devices that I saw mentioned elsewhere on this forum. These devices are supposed to provide a better seal than caps.

At the moment I’m leaning towards getting the FreezeCap devices and using Nylog Blue.

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Tim wrote: Mon Sep 07, 2026 1:08 pm Never had a problem. If the individual is wrenching a service cap down hard enough to strip the threads. They should not be working on the vehicle. New valve core and Brass cap, best option out there.

Cusser wrote: Tue Sep 08, 2026 5:30 am

jfklein wrote: Mon Sep 07, 2026 1:05 pm I'm thinking that perhaps VW uses plastic caps to prevent damage to the aluminum threads.

No, it's that plastic caps are cheaper.

jfklein wrote: Mon Sep 07, 2026 1:05 pm So if somebody overtightens the cap, the threads on the cap will strip first.

The caps have an internal rubber seal. Only an idiot would crank those super-tight.

.

Maybe stripping the threads isn't realistic, but there's also the risk of cross-threading.

To avoid the risk of stripping the threads or cross-threading, I turn the caps in reverse (left-y loose-y). When I feel the cap "bump" over the first thread, I proceed to thread them on (right-y tight-y) and snug them up.

I took some better photos of the rims of the high and low side service ports in my VW GTI. See below.
Do you think the little nicks and dents in the rims are affecting the seal of the cap o-rings? If so, how would I fix the rims to get rid of the nicks and dents?