Possible AC refrigerant leak source
 

I had a previous thread talking about our HVAC. Our system is a heat pump which is all matching Trane and dated 1991 (indoor, outdoor and thermostat are all a single system and all dated 1991). The aux and emergency heat is electric.

When we were sold the home, the PO told me "I used to do AC. Once a year, I top up the freon and it works fine, but it's old." A few weeks back before we had several folks in the house and when it had started getting warm, I noticed that the AC wasn't cooling at all. I called a guy who came out and said he put 9# in the system.

You guys said 9# was a ton and a leak should be easy to find because there'd be lots of oil. I turned the AC off the other day and poked around the indoor unit and the outdoor portion and didn't find anything that seemed super obvious, but a lot of the indoor portion of the system is hard to see.

This was the only thing that looked remotely wet or oily. It's missing a cap. I put some water in it and was able to see on occasional tiny bubble pop up from down in the area where the allen wrench would go. I don't know if that was just air working it's way out of dirt or if it's a place that can leak.

http://forums.pelicanparts.com/uploa...1618180689.jpg
http://forums.pelicanparts.com/uploa...1618180689.JPG

The AC seems to be working really well now that it's charged despite the fact that it's 30 years old and the attic space heat management is not good.

We'd like to get the roof replaced and hold off on the HVAC until after the summer. (Actually, I'd like to do both ASAP, but you do work around a budget a bit).

That may be your only leak on that system.
The occasional bubble may be more than occasional when the system is running during high outdoor temperatures.
I cannot believe (maybe I can) that any HVAC guy worth one's salt wouldn't find a replacement cap for that.

Is a cap (and maybe a little cleaning) all it would take?

I can probably find a cap.

You could glue a cap on there, or you could have your A/C guy sweat in a new valve while R&Ring the freon.

I would think it shouldn't be that hard to get a new cap, right?

Would a glued on cap seal as well as a proper screwed on cap?. Why would it bed to be glued on?

That is a valve that was used to release the original refrigerant charge from the condenser & compressor unit into the lines and evaporator when those were installed and evacuated - the bubbles mean that it is leaking. You can find a cap at Ace but will have to really clean the threads on the valve body and then use a sealer, such as Nylog or similar, on them since the cap area is not a flared fitting.

Common leak area. You should be able to find a cap for it. Do a search for "service valve cap" or call a Trane dealer. They probably have an old unit sitting around somewhere with a cap on it.
Are the caps on the gauge ports tight enough it requires a wrench to remove them? If not, snug those down as well.

Thanks, all.

Yes, the other caps are not hand tight.

If you can't find a cap, I think I could find one and mail it to you.
They are a common valve type.
They seal on the top edge.

You can make a soap bubble solution water and dawn, you will know quickly how bad that leak really is. I have a background in HVAC and REFRIG, the typical leak source on a system that old is your evaporator , which is to coil in the air handler unit.. This is accessible behind panel door on that unit HVAC guy should have no problem finding a leak on that coil They have electronic leak detector that can find leaks less than an ounce a year. If you want to check it yourself use the soap bubble solution in a spray bottle and saturate coil make sure you cut power of to unit since your blower motor is close to evaporator. Give it some time for bubbles to form Have a good flashlight.
If by chance that is where leak is located. You can replace evaporator however don’t recommend spending that money better to replace with new system. Hope it’s the service valve as far as the cap HVAC contractor or HVAC supply house in your area should be able to help

Thanks, hopefully, I'll be able to find it locally or online. If not, I'll certainly let you know.

Walk or drive over to your least friendly neighbor's house and ask if you can look at their A/C unit. Bring someone along to distract them. Then look at them and say "Huh! Mine is missing that cap too!" Problem solved! :D

OK, now I'm a little confused. I took my handy vernier caliper out and measured the diameter of the top and at the threads and it seems to be .545" which is quite a bit bigger that 1/2" or smaller than 9/16".

Hmm, looks like that may be a 3/8" cap. I found one on the web that says it's a 3/8" cap, but 5/8 OD and 9/16 ID. I guess 3/8" is the ID of the line or something like that.

I assume the correct cap would be a compression (concave taper/bevelled) cap (therefore not NPT or obviously not flare).

https://images.thdstatic.com/product...610-64_600.jpg

or should it be like this?

https://m.media-amazon.com/images/I/..._AC_SS450_.jpg

Flat cap, not flared. If my knee wasn't gimped I'd walk outside and measure my cap. It's a pretty standard cap. I'd call the local Trane dealer. Tell them you need the top cap for a liquid line service valve.

thanks. Will do.