problem measuring a/c high side pressure

J

JDEstill

Turboliscious!
Joined
May 26, 2001
I need to do a little troubleshooting on my a/c. It's still got R12 in it, so the two Schraeder valves are stock. At least I think they are - my hard lines that run across the top of the radiator were replaced back in the late 90's, I think with an OEM hose set.

The high pressure port on the hard lines is smaller than the low pressure port on the drier. I have an R134 gauge set, which seems to fit the low pressure port, but not the high pressure. Went to friends house, he has an ancient R12 gauge set, and his gauges fit the low pressure port but not the high pressure. So I am momentarily stuck!

Thinking my best option is to find a high pressure hose that will fit my gauge set on one end and fit my high pressure port on the other end. Or, if that isn't feasible, just buy a new R12 gauge set that will fit up ok. But I am worried about just ordering a cheap gauge set - since my friend's set did not fit, how do I know that a brand new gauge set will fit? The internet searching I have done has turned up some fairly inexpensive gauges sets, but they never specify the fitting sizes. So can someone educate me here? Anyone know where I can get the proper hose, or the proper gauge set, or something?

Thanks

John
 
There is an adapter for the high pressure side. It was made a different size so that folks couldn't easily try to charge on the high side (blows up the can).

RemoveBeforeFlight
 
My friend's R12 gauges do NOT fit. Like I said, his low pressure hose fits the low pressure port, but the high pressure hose appears to be the same size as the low - swapping hoses around doesn't help.

RBF, are you saying that the hose ends are supposed to be the same, but there is an adapter that is used to connect the hose to the high pressure port? If I understood that right, is that adapter commonly included in new gauge sets? Also, such an adapter does not require taking the core out of the high pressure Schraeder does it? I'm not interested in depressuring my system!

Another question - it seems like my R134 gauge set fits the low side - is it supposed to? For some reason I was thinking the fittings were different on both low side and high side.
 
Some pictures, this adapter has a push pin to activate the valve as the hose end is attached to it. Thread this onto the high pressure port, then connect the hose. Click on pic for full size.

AC_Adapter_00.JPG AC_Adapter_01.JPG

This one is steel, they are also made in brass. For a bit of trivia, in '91 GM went to a different high pressure port, a recessed valve type that requires yet another adapter. Note that these adapters aren't meant to be left in place. Just used during servicing.

As for the R134a hose end connecting the the low pressure port, from my understanding it shouldn't. The R134a ports use a completely different thread along with a flat gasket seal. It may be that there is just enough thread engagement.

RemoveBeforeFlight
 
cheat...

Go to autozone an buy the R134A adapters for 12 dollars. Screw them on the R12 fittings. Use he R134a gauges to charge your R12. its not like the compressor is gonna know ... just make sure you set by pressure and have a temp chart on had for correct charge fill.
 
I was at the zone the other day and I looked at the R134 adapter fittings. It looked to me like using them required pulling the core out of the existing Schraeder valves. Not true? Because I sure ain't doing that! :) That's why I was figuring I needed an R12 gauge set.

RBF, thanks for the above pics. Is it expected that the adapter be included in a new R12 gauge set?
 
JDEstill said:
I was at the zone the other day and I looked at the R134 adapter fittings. It looked to me like using them required pulling the core out of the existing Schraeder valves. Not true? Because I sure ain't doing that! :) That's why I was figuring I needed an R12 gauge set.

RBF, thanks for the above pics. Is it expected that the adapter be included in a new R12 gauge set?
Click to expand...
There are some tha screw on over the existing ones like a sleeve and use the existing core


Posted from the TurboBuick.Com mobile app
 
JDEstill said:
RBF, thanks for the above pics. Is it expected that the adapter be included in a new R12 gauge set?
Click to expand...

Not that I know of. There may be gauge sets out there that are supplied with a variety of adapters, but you would likely be paying for more then you need.

IIRC, I got the two I mentioned at a CarQuest store. Needed to be ordered, but were there within a day (maybe 5 now since they are older cars).

This appears to be the proper adapter:

http://www.es-refrigerants.com/products/details.asp?id=260&t=316quot;-to-14quot;-adapter&Trying=ON

Also, I've been using ES-12a in the R12 systems. Works much better and is cheaper then R12 or R134a. Note that ES-12a cans require a R134a tap valve.

RemoveBeforeFlight
 
I believe the high side fitting is a 3/16" sae flare connection. A standard set of R12 gauges are 1/4" sae flare (non automotive).. the adapter or hose should be available at your local parts store. Maybe try calling an auto air shop and inquiring.. had this issue last summer but got busy on other things and haven't gotten back to it (buick in garage not being driven :( ).. I will check for myself maybe tomorrow and post unless I see the solution posted here first

Posted from the TurboBuick.Com mobile app
 
RmvBfrFlght said:
Not that I know of. There may be gauge sets out there that are supplied with a variety of adapters, but you would likely be paying for more then you need.

IIRC, I got the two I mentioned at a CarQuest store. Needed to be ordered, but were there within a day (maybe 5 now since they are older cars).

This appears to be the proper adapter:

http://www.es-refrigerants.com/products/details.asp?id=260&t=316quot;-to-14quot;-adapter&Trying=ON

Also, I've been using ES-12a in the R12 systems. Works much better and is cheaper then R12 or R134a. Note that ES-12a cans require a R134a tap valve.

RemoveBeforeFlight
Click to expand...
Maybe I should learn to pay attention to previous posts lol :oops:

Posted from the TurboBuick.Com mobile app
 
Looking at my R134a gauge set, I am nearly positive that the fittings off the manifold are 1/4" SAE, and the hoses are 1/4" on both ends (with one end having a push pin to depress a Schraeder valve). Then there are two quick connect fittings that screw onto the end of the hoses. I should state that I have never used this gauge set before, LOL, so I'm trying to figure out exactly how these pieces are supposed to work! So it seems like the quick connects will snap onto R134a fittings? My gauge set is identical to this one: http://www.harborfreight.com/a-c-manifold-gauge-set-92649.html
The hose, without the quick connect on it, seems to fit on the low pressure port nice and tight, so I'm pretty sure all I need to make this gauge set work on my car is the 3/16" x 1/4" adapter. Sound right?
 
JDEstill said:
The hose, without the quick connect on it, seems to fit on the low pressure port nice and tight, so I'm pretty sure all I need to make this gauge set work on my car is the 3/16" x 1/4" adapter. Sound right?
Click to expand...

Yes, I had to look at the manual for the gauge set to see what they did for hoses & fittings. Note that the yellow charge hose end won't fit a R12 can tap. Only a R134a can tap.

RemoveBeforeFlight
 
Thanks RBF, I think I can find the adapter somewhere around here. My gauge set is actually US General instead of the Pittsburg set I linked to. Identical set, but that Pittsburg manual is 100pct better than the USG one! Glad you referenced it, I think I will print it out and keep it with my gauge set, and throw away the useless manual that came with it originally!

John


Posted from the TurboBuick.Com mobile app
 
First question is what are you troubleshooting?
Click to expand...

My air conditioning?


LOL - my a/c has been essentially depressured for the last 5 or 6 years, though it was still holding 10-15 psi. Put an unknown quantity of R12 in it, and it blows cold again, but need to make sure it has the right amount, and need to check both pressures to make sure nothing is plugged up or the compressor is failing or anything like that. I'm sure once I get some good pressure measurements I'll be back with more questions.
 
Did you put it under a vacuum to see if it holds first before pumping $600/lb of R-12?
Did you change out the orifice tube and see if there is any water in the system?
 
Lol, good answer. Actually what you said helps. There is a leak and r-12 is going for thousands a can when you can find it. You need to find the leak. Best thing to do is bite the bullet and switch to 134. Pull a vacuum first, like horndog said, once it's pulled down, shut everything down and come back in a hour or so. If the needle holds your good, if not you will need to add leak detector and find that leak. The conversion is easy and mine blows so cold that I have to turn the vents away from my legs.
Just so you know you can get pretty close to the right charge just using the low side. Both are used more for troubleshooting The gauges that come on cans from the parts stores are low side only. I'm a facility manager but am licensed for A/C. I can charge by either side, using both just gives you more info and tell's you where to look for problems. I would rather have only the high side if I had to pick, but it can be done. For instance I know that r-22 on a 80 degree day should show around 225-235 on the high side and 70 on the low. That's if everything is working correctly and the house is at normal temp on the inside.
Hope this helps, let us know how things go. -Jeff
 
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