SOLVED: Thread pitch/type to plug AC compressor manifold port?

[Dustin_89BII]

Hi folks,

just installed new AC components under the hood and annoyingly can’t find the right plug for this aftermarket manifold. I came close with the black 20tp plug. It almost threads in.

Any help would be appreciated! Can’t even determine if it’s metric or SAE

 

[franklin2]

Looks like it's a 12mm thread. I was searching, and what gave me some hits are what they call "A/C block-off kit and line terminator". They make these plugs for the A/C systems to block off rear A/C on dual A/C systems and other purposes.

One I found was a Dorman 801-020. Keep looking, maybe you can find something better. I am pretty sure looking at your fitting you will need a o-ring in there.

 

[Curious Hound]

I agree with trying a find thread M12. Probably 1.25mm thread pitch. It looks pretty fine. It also looks like parallel pipe threads, not tapered. That makes a difference. I wouldn't be surprised if the proper plug for that has a large head and flange and seals with an o-ring or copper washer.

What you're holding in the first picture looks like a setscrew and not a pipe plug.

 

[Dustin_89BII]

Thanks so much for your help, guys. I think I might order these in m12x1.0 & 1.25 and see if it can work.

 

[Curious Hound]

Thanks so much for your help, guys. I think I might order these in m12x1.0 & 1.25 and see if it can work. View attachment 95316

I think you're onto something there.

 

[Dustin_89BII]

Well, neither of the plugs I ordered from my previous post worked!
M12 x 1.0 & 1.25

I think m12 looks good. Seems straight walled. Seems like the 1.0 pitch is damn close, more than the finer 1.25… but it only threads in bout 3/4 of a turn.

what am I missing here? Is there a different thread format, akin to ACME that is common here? It’s sooo hot here, lol

 

[Curious Hound]

You could try measuring it with a thread gauge. You could get a cheap gauge from Harbor freight or local auto parts store. Get one in metric and another in SAE. That would help you narrow down the thread pitch.

1.0 is actually finer pitch that 1.25. In metric threads, the pitch is in millimeters. It’s the distance from one peak to the next or one valley to the next. So, M12 X 1.0 is 12mm diameter and 1.0 millimeter thread pitch. M8 X 1.25 has an 8mm diameter and 1.25mm pitch.

for SAE (non-metric) threads, the pitch is expressed in too or threads per inch. So, a 1/4-20 screw is 1/4” diameter with 20 threads per inch.

pipe threads can be tapered or parallel. Most common pipe threads are tapered. So, as you tighten them, they wedge together tighter and tighter to form a seal. So, a 1/2” NPT fitting is 1/2” nominal pipe diameter (pipes are measured by inner diameter) NPT stands for national Pipe Tapered. Less common would be BSP - British Standard Parallel. However, in the machinery world, metric parallel threads are very common. An example would look like what you have and be designated M12X1.0 Metric Parallel. Parallel pipe threads do not wedge together. So, provisions must be made to seal them with O-rings or soft copper or aluminum washers.

then there are other special threads for high pressure systems like JiS, AN, etc.

yes. It gets confusing

 

[Snoranger]

Sounds like it’s -5 straight thread o-ring seal. That’s a 1/2”x20 thread. Try a 1/2”x20 (fine thread, SAE, whatever’s you want to call it) bolt. It that’s right, find the right fitting.

 

[franklin2]

Where did you get the pipe? What model is it for? It would probably be for a high pressure switch or something like that. Just buy the sensor and screw it in.

 

[Dustin_89BII]

You could try measuring it with a thread gauge. You could get a cheap gauge from Harbor freight or local auto parts store. Get one in metric and another in SAE. That would help you narrow down the thread pitch.

1.0 is actually finer pitch that 1.25. In metric threads, the pitch is in millimeters. It’s the distance from one peak to the next or one valley to the next. So, M12 X 1.0 is 12mm diameter and 1.0 millimeter thread pitch. M8 X 1.25 has an 8mm diameter and 1.25mm pitch.

for SAE (non-metric) threads, the pitch is expressed in too or threads per inch. So, a 1/4-20 screw is 1/4” diameter with 20 threads per inch.

pipe threads can be tapered or parallel. Most common pipe threads are tapered. So, as you tighten them, they wedge together tighter and tighter to form a seal. So, a 1/2” NPT fitting is 1/2” nominal pipe diameter (pipes are measured by inner diameter) NPT stands for national Pipe Tapered. Less common would be BSP - British Standard Parallel. However, in the machinery world, metric parallel threads are very common. An example would look like what you have and be designated M12X1.0 Metric Parallel. Parallel pipe threads do not wedge together. So, provisions must be made to seal them with O-rings or soft copper or aluminum washers.

then there are other special threads for high pressure systems like JiS, AN, etc.

yes. It gets confusing

Thanks for all this good info! It really helps. Cheers!

 

[Dustin_89BII]

Sounds like it’s -5 straight thread o-ring seal. That’s a 1/2”x20 thread. Try a 1/2”x20 (fine thread, SAE, whatever’s you want to call it) bolt. It that’s right, find the right fitting.

Thanks for the comment. Yeah 1/2” x 20 is really close as well. But it doesn’t go in very far. Maybe 1/2-3/4 of a turn!

 

[Dustin_89BII]

Where did you get the pipe? What model is it for? It would probably be for a high pressure switch or something like that. Just buy the sensor and screw it in.

I found out that the port in the manifold that I’m trying to plug is for a high pressure release valve. So the threads are for that. so I’m either continuing down this road— getting a plug or HPRV, getting an older manifold that doesn’t have the port, or just drilling and tapping for a known thread pitch! Good lord this had been way too much work for this little thing. Thanks for commenting.

 

[Dustin_89BII]

Franklin2 got it right. I was able to get a pressure release valve to work on the manifold. Thanks so much everyone for the support! Found the valve online at cold hose.