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Old 07-24-2012, 09:14 PM
  #16  
dr bob
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If you are reading PS I for vacuum, you have the wrong gauges or your pump sucks poorly. (Had to think about that a bit...). My industrial/lab pump does everything but bend the needle over the stop pin on my Robinaire gauge set. So if your anywhere near sea level, try a more serious vacuum gauge to verify that you have enough suction to boil out all the moisture in your system. Just a little bit of air will trash the system performance, and a little moisture loose in the system will hurt the expansion valve and eventually perforate the evaporator. A few PS I of partial air pressure in the system will easily cost you twenty hot-day degrees of cooling at the evaporator. I've listened to more than a few DIY experts who report awesome vent temps as low as fifty degrees, don't need no stinkin' vacuum pump! Just sweep the system. They are way wrong.
Old 07-24-2012, 09:23 PM
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Speedtoys
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Well...I get lower than 50, 38d on a "not sure if its REALLY full" charge or not..because I have an unknown actual size system at the moment.
Old 07-25-2012, 07:53 AM
  #18  
griffiths
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Originally Posted by Speedtoys
I have a 3Hp dual stage vac pump..appears to work well.

But the -same- pump, on two different sets of HF gauges, read different vacuums by 2-3psi.

Gotta love HF.
I guess you mean under vacuum you are seeing different readings by 2-3 inches of mercury. If you are using a common analog (mechanical) gauge you will find with most of these type gauges it can be difficult to determine exactly what the reading is because the printing width of the increments on the gauge face vs. the width of the needle. I recall one time I had a low side gauge that was giving me different readings every time I bumped it. So I smacked it with my hand the needle move 5" !

So we moved on to electronic or digital gauges, however here to, depending upon the voltage of the battery, we notice variations in measurements but not to the degree as you find with less expensive analog gauges. On occasion we use 2 digital gauges on the same manifold set, both set to read in microns vs. inches of mercury, and the 2 never present the same reading; one of which needs to be 'zero'd' out before each use (add the 2 and divide the sum... lol).
And I'm sure if we sent the 2 digital units to different calibration labs we get different findings.

So if you are going to make A/C a full time occupation then invest in a good quality digital gauge that offers both micron and inches of mercury readings.
(I believe Robin Air and Tif are just a few sources you can explore).



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