HVAC drain line cleanout: shop air -> ? -> oversize Schrader valve
May 29, 2024 6:08 PM   Subscribe

I have an HVAC drain line with a cleanout valve. I need to connect shop air to the fitting on one side of the cleanout, but am at a loss for how to find the connecting part. Details and pics below.

The HVAC unit in my attic has a primary drain line that connects to the sink drain in one of the bathrooms. In the attic, near the HVAC unit, is a valve in the drain line. On either side of the valve is a brass fitting with what appear to be 7/16"x20 threads on the outside, and a thing that looks like a Schrader valve (like on your tires, only larger) on the inside.

The idea is that you can close the valve, connect pressurized gas to the fitting on one side of the value, and blow out any clog on that side.

Here is a photo of what the thing looks like in situ: Exhibit A.

(Note that I have removed the plastic cap from the fitting on the left, but left it in place on the identical fitting to the right.)

My question/problem: What fits this fitting? (That's in service of answering a broader question: How do I get air from a shop compressor into this thing?)

I have a feeling this is a question which would be answered by a very quick web search if I but knew the correct names for the things in question. (Gentle reader, I assure you that I am reasonably handy -- though lacking HVAC-domain-specific knowledge, and have searched diligently in vain.)

I have even gone to the extreme of visiting my local brick-and-mortar HVAC parts shop and talking, face-to-face, to another human in meatspace, much as extroverts are said to do. They suggested this thing might work.

Narrator: That thing did not work.

I can't push the tip into the fitting far enough to make the Schrader valve open, so even if I could make a good seal, no air would flow.

I suppose another option would be to temporarily remove the Schrader valve. I tried using an automotive valve stem wrench but it did not fit.

Any suggestions or help would be appreciated. Thanks!
posted by sourcequench to Home & Garden (8 answers total)
 
Best answer: The valve seems to be a Searco QB1 blowout isolation valve. There is a whole thread on it here with someone else with a similar problem and a video that might be helpful. The required part seems to be something commonly used in the hvac business and known as a "gauge hose".

That MIGHT be something like this.

It reminds me of connections I've seen while recharging automotive a/c units but I don't know anything special about this subject beyond that.

Presumably this type of connector is used simply because it is a common size most HVAC people will typically have on hand.
posted by flug at 7:13 PM on May 29, 2024


Searching on hints from flug's links I found a (c) 2021 link PROPRIETARY ESP PRODUCTS with a picture of your valve and contact info
posted by tinker at 7:53 PM on May 29, 2024


Best answer: This catalogue page has a question about the connection and the answer says 1/4" flare. Looking at the picture, that seems reasonable.

The plumbing supply or HVAC shop should be able to set you up with the right parts to go from flare to Schrader, or other options to connect to your air line. In fact it looks like Amazon has exactly what you need and it even mentions that it is for blowout systems...
posted by snoboy at 8:17 PM on May 29, 2024


For other non Amazon options (maybe helpful at the HVAC or Plumbing supplier) my Google search was on "1/4 flare fitting female x schrader valve".
posted by snoboy at 8:24 PM on May 29, 2024


It looks like you've got a few valve connect answers here.

"How do I get air from a shop compressor into this thing?"

A portable air tank. Just charge it up with your compressor, carry into the attic.

I'd lend you mine, but I'm 3,000 miles away.

Maybe you can borrow one from a tire place, their tow trucks usually have one.
posted by Marky at 12:51 AM on May 30, 2024


Can you push the blower bit that you bought with the rubber cone into the end of the pipe in the drain pan? That way you can bypass your odd ball valve with Schraderish valves and just go straight down the pipe?
posted by gregr at 6:19 AM on May 30, 2024


Response by poster: Thank you all for the answers upthread. To summarize what I've learned (from this thread, elsewhere on the web and empirically):

The fitting housing (not considering the Schrader-style valve inside) does indeed appear to be called 1/4" SAE male flare. The 1/4" part (I'm speculating) is related to the ID. The outside is 7/16" x 20 TPI (verified by putting a thread checker on the fitting).

The thing intended to mate with this (and, simultaneously, hold the Schrader-adjacent valve open) is known as a "gauge hose", "refill hose" or "Guatemala hose". It appears to be available as part of (generally, expensive) kits intended to measure the pressure of and/or add refrigerant to the closed coolant loop in air conditioning systems. Use to put pressure down a drain line appears to be an "off-label" use.

The path of least resistance, for now at least, appears to be obtaining the right size valve stem wrench, temporarily pulling the Schrader-alike thingy out of the fitting, then using a rubber-tipped air tool I already have to shove air into the hole. (I don't need a permanent, positive or leak-proof connection; just ~40psi for a couple seconds.)

I will update here when I've tried that approach. (ETA this weekend.)

I've already got a portable air tank and long air hoses, but thanks to Marky for the thought.

The pipe in the drain pan is in a position where I can't really put tools on it without significant disassembly of the system. (There is _a_ pipe I can reach, but it's for the overflow drain.)
posted by sourcequench at 11:59 AM on May 30, 2024


Response by poster: Removal of the valve core and using a rubber-tipped air tool did the job.

I got a cheap set of valve stem wrenches intended for automotive A/C work, and it had a size that did the trick.

Managed to launch the drain plug from the bathroom sink a good distance, too.

Thanks again to all who replied.
posted by sourcequench at 11:45 AM on June 4, 2024


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