Help Identifying Cap I Found and What It Goes To

[2002_KJ]

I found this plastic cap in the air cleaner box when I was changing my filter:

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While I was trying to figure out what it was and where it goes I noticed that it actually screws onto that valve(?) in the picture below, which makes sense that I found it in the air cleaner considering how close it is to the inlet...but what exactly is that valve? There's another smaller valve that looks like it closer to the air cleaner/fender and I think it's also missing a cap. Is that where the cap I found is supposed to go, screwed on tight? Anything important? I checked the service manual but couldn't figure out what that tube/valve is for. Any ideas? Thanks.

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[klc]

I believe that’s part of your air conditioner.

 

[tommudd]

Yes part of the AC system

 

[klc]

One valve is for adding refrigerant, the other IIRC is for evacuating the system after repairs.

P.S. Viva il Giro!

 

[Techdad]

That is not completely incorrect.
When the A/C is being maintenanced using a proper gauge set with 3 hoses, one valve is the connection to the "high side gauge" hose and the other valve is for the "low side gauge" hose. They are different sizes so they cannot be installed incorrectly. When changing the system with a proper professional "gauge set" (not a Walmart can with one hose), the low pressure, or (suction) side is where you allow the freon to be sucked into the system via the 3rd hose using a valve (on) the low side gauge. When the high (and) low gauges both read the proper pressure and the cool air at the dash is the proper temp drop, the system is now charged correctly. Don't let the term (suction) fool you. Both sides are under GREAT pressure while the A/C is running. But the pressure on the suction side is much lower, thus it is referred to as the low side.
When the system is not running, both valves will have the same pressure.
The high side is called that because it is the output of the compressor, very high PSI hot gas going to the condenser coils to be cooled by the fan.
Keep those caps on to keep contamination out of the valves. Any crud in there can get into the system when a gauge set in installed and could cause damage. A tech probably dropped one and didn't see where it went. Sometimes there is a red cap for the high side and a blue for the low side. When charging with a one hose Walmart can, yes, it goes on the low (suction) side valve. But it is actually under pressure. But less than the can.

 

[2002_KJ]

Thanks guys. Watched a few YouTube videos on this and now I understand, including one using the gauges Techdad mentioned.

Glad I found that cap! Just need to find a replacement cap for the low pressure line now. Ciao.

 

[dkcase]

There are valve cores inside those ports, like tire valves. But I've seen it said that manufacturers say the real sealing DOES DEPEND on these caps.Should be o-rings inside them.

 

[2002_KJ]

There are valve cores inside those ports, like tire valves. But I've seen it said that manufacturers say the real sealing DOES DEPEND on these caps.Should be o-rings inside them.

Upon closer inspection those valves are a little gunky inside...no doubt because the caps were off for a long time...