Found two mystery caps in the grass by my condenser and got them back where they belong

Same thing happened to me last fall, except I only ever found one of mine. I was raking leaves around the condenser and the rake kicked up a single brass cap from under the honeysuckle by the fence. The other one I never did locate, probaly went over the fence line into the neighbor's brush pile years ago. The one I found threaded right onto the bigger line by hand, no tools needed. The open port with no cap had a bunch of dirt and grass clippings crusted around it, so I cleaned it off gently with an old toothbrush before putting anything near it. Didn't want to push grit down in there. When I mentioned it at my next service call, the tech just handed me a spare cap from his truck and screwed it on in about ten seconds. He said the caps mostly keep junk and moisture out of the valve, and that they're a secondary seal on top of that. He also told me hardware stores and supply houses sell them loose for a couple bucks if I ever lose another. Now I do a walk-around with a flashlight every October when I'm winterizing the yard, mostly because I got tired of mysteries turning up in the grass.

Funny timing on this thread, because I did the opposite cleanup job last month. Instead of finding caps in the grass, I found mine rattling around loose on the lines when I went to hose pollen off the unit. Somebody, maybe me, maybe the last tech, had left them finger-tight and one was about half a turn from falling off into the mulch. What I learned from that little episode: the caps actually matter more than I thought. On my Carrier, the bigger line's cap is what keeps dirt out of the service port, and if the little valve inside leaks, the cap is the backup seal. Mine had a cracked rubber gasket inside, which explains why I'd been smelling a faint oily whiff near the unit all summer and blaming the neighbor's grill.

I ordered a two-pack of replacements online for a few bucks and now keep the spares in the garage cabinet with the furnace filters. Hand-tight is right, like you said, no wrench needed. If you gorilla them down you can wreck the threads and then a tech has a real problem next visit.

One thing I'd add to your spring reminder: give them a quarter turn to snug up while you're out there, since temprature swings over a season seem to loosen them a touch. Also worth checking wether yours have the little o-ring inside at all. Some cheap aftermarket caps come dry and they're basically just dust covers at that point.

Gotta push back on the tech's take in the earlier reply though. He called the caps a secondary seal, and sure, technically a good cap with a rubber gasket does seal, but if someone's system is actually holding refrigerant only because a little plastic cap is tight, there's a leaking valve core under there. The cap is a dirt cover first and foremost. When my core weeped a while back the tech swapped the core, he didn't just crank a new cap on and call it done. If anyone reading this finds thier caps were off for months and still has decent cooling, fine, but if you ever notice oily residue around the valve, that's the actual problem, not a missing cap.

Reading this made me go check my own unit tonight and now I have a worry. My toddler was out with me while I looked, and he kept trying to poke the little pin thing in the middle of the valve with a stick before I stopped him. It hissed a tiny bit one time when he hit it. Did he maybe let some of the cooling stuff out, or is a quick press like that no big deal? Also now I realize one of my caps is plastic and the other looks metal, which seems wierd for the same unit.