Automotive Air Conditioning Information Forum

For the past fer years I've had to top off the 134a in my 2000 Chevrolet pickup in the summer. I know both service port valves have a slow leak but I haven't wanted to evacuate the system to replace them. I've read that the service port caps are intended to be the primary seal and the service port valves are intended to be used to service the system. Are the plastic caps really supposed to hold up to the 134a pressures? Are there metal caps specifically intended to address service port valve leaks?

The plastic caps are essential. I keep an assortment kit on hand because many of the cars we work on are missing them .Get a schrader tool and be sure your stems are snug, not tight. This may not make much sense but it works!
I have never found metal caps

tbirdtbird wrote: ↑Tue Jun 04, 2024 12:16 pm The plastic caps are essential. I keep an assortment kit on hand because many of the cars we work on are missing them .Get a schrader tool and be sure your stems are snug, not tight. This may not make much sense but it works!
I have never found metal caps

I have the plastic caps on the service ports but they are probably the original caps. I know they seal a little because I can hear some pressure release when I remove them but I don't know if they are just holding some pressure and then start venting after they reach a higher pressure. Do the caps get old and need periodic replacing?

I have a Schrader tool and have verified the low pressure side doesn't stop leaking when I play with it. The high side uses a ball valve so there is nothing I can do other than replacing the whole service port.

On a 20 yr old vehicle it wouldn’t be a bad idea. Inside the caps there is a rubber seal.
The caps will not leak after system pressure builds up. I know it seems impossible but it just works.
I had 8 cars all lined up at my shop with all the owners standing by.
Engines at speed.
With caps off, 13 of the 16 of the ports set off the sniffer. Once caps were applied, there were no leaks

tbirdtbird wrote: ↑Tue Jun 04, 2024 1:40 pm On a 20 yr old vehicle it wouldn’t be a bad idea. Inside the caps there is a rubber seal.
The caps will not leak after system pressure builds up. I know it seems impossible but it just works.
I had 8 cars all lined up at my shop with all the owners standing by.
Engines at speed.
With caps off, 13 of the 16 of the ports set off the sniffer. Once caps were applied, there were no leaks

Thanks, I'll give new caps a try and see what happens next year.

tbirdtbird wrote: ↑Tue Jun 04, 2024 12:16 pm The plastic caps are essential. I keep an assortment kit on hand because many of the cars we work on are missing them .Get a schrader tool and be sure your stems are snug, not tight. This may not make much sense but it works!

Just under a month ago, investigating poorer-than-typical AC performance in my 1998 Frontier, I found that the high side cap was actually broken, in two pieces. And not all pink/red high side caps would screw in !

tbirdtbird wrote: ↑Tue Jun 04, 2024 12:16 pm I have never found metal caps

Back in the R-12 days there were some metal caps, on vehicle AC and even on some refrigerators.

Cusser wrote: ↑Wed Jun 05, 2024 7:39 am Back in the R-12 days there were some metal caps, on vehicle AC and even on some refrigerators.

Yes, my 1980 Toyota R12 system has metal caps. And every home HVAC system I've owned had metal caps. But I haven't found any for R134a systems other than decorative ones. But if the plastic caps are designed to seal against the 134a pressures then I'm fine with them.

Should have clarified what I have observed.
Of course R12 and resi/commercial have metal caps.
So why not 134 systems?

I have plastic cap kits for use on cars whose caps have been misplaced; usually on a port that is difficult to get to. There are at least 3 cap systems all with different pitches. Why?

We also have had the inside male stem of the female cap break off. It is not stuck in hard. Using a tiny pick tool you can walk it out . You may need to use 2 such tools.
Try to remember that you don’t have to crank the caps on to 100 ft lbs. All they need is snug.
Be sure to have new caps available right away, this is just to have the correct size available. You will lose precious little refrigerant this way.

tbirdtbird wrote: ↑Thu Jun 06, 2024 12:46 pm I have plastic cap kits for use on cars ... There are at least 3 cap systems all with different pitches. Why?

Why did GM and Ford use different R-12 high-side fittings once those were mandated to be a smaller size than the low side?

tbirdtbird wrote: ↑Thu Jun 06, 2024 12:46 pm We also have had the inside male stem of the female cap break off. It is not stuck in hard. Using a tiny pick tool you can walk it out

This is what I did on my 1998 Frontier, about 6 weeks ago. I had lost refrigerant, and when I went to investigate pressures with my gauge set, found the high-side cap was broken when I unscrewed it.