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Taking Pressure Readings

tomibriggs on Mon July 13, 2009 7:09 PM User is offline

Does taking pressure readings often decrease the amount of the refrigerant in the system? If yes, is it significant enough to affect the performance of the a/c? I'm just wondering what happens to the refrigerant in the hose between the service port & manifold guage on both the hi & low side whenever I take pressure readings.

Cussboy on Mon July 13, 2009 11:57 PM User is offline

Yes, it decreases the amount of refrigerant; but only a tiny amount, if done correctly, so not significant.

Edited: Mon July 13, 2009 at 11:58 PM by Cussboy

GM Tech on Tue July 14, 2009 8:20 AM User is offline

You can "suck" the refrigerant in the hoses back into the system- by shutting off high side at the car connections- then open both gage valves- let it all back into the low side- except for a minimal amount. or if the old style r-12 hoses- use the check valves on the ends- commonly called freezeless adapters- work the same way.

I am spoiled with a machine- I just suck it back into the machine- never lose a drop.....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Tue July 14, 2009 9:34 AM User is offline

If your gauges sat around for awhile, even with check valves, can almost bet your life you will have air in them. But for just taking pressure readings, make sure both valves are closed and don't take a half a day to attach them to the ports. Either Schrader R-12 or quick coupling R-134a ports will release a certain amount of refrigerant, do it quick. The air in the lines doesn't hurt anything as the pressure of the refrigerant is far greater. But if you read zero, doesn't make any difference anyway, you already have air in your system. You never open the manifold gauge valves while doing a pressure test, and have to remove the port couples, just as fast as you attached them.

Either valve gives a route from either the blue or red hose to the yellow, if both are opened, not only between the yellow, but between the red and blue as well. If intending to top off, that air in the gauge lines has to be removed first, normally done by purging that in itself is a guessing game.

I prefer adding a valve to the vacuum pump and teeing that in with the refrigerant source with both gauge valves closed, refrigerant source comes with a valve. With all valves closed, can open and run the vacuum pump to purge out all the air, close it, then open your refrigerant source valve, then the low side with the engine running at 1,500-2,000 rpm to add refrigerant.

Would think such a tee and valve would be commercially available, is available in a four valve manifold gauge, but I couldn't find one, so had to make one. Okay, show a site where such a tee is available.

Yeah, it's nice to have a charging machine with the gauges, tank, vacuum pump all built into it, but still have to be awake when turning knobs and valves. Ha, and also a refrigerant identifier, don't leave that out we the screwed up mess the EPA has made today and all this garbage on the market due to the killing of the FTC with tons of false misleading claims.

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