jroode32,
Congratulations on your first success! Quite a thrill when you see that frost forming, isn't it.
But you do have some tweaking to do to get things really going in the right direction...
Quote:
Originally Posted by jroode32
...it is a HF pneumatic powered venturi style pump. After doing some research on that pump I found a lot of people reported 28" hg and for just a few extra bucks I thought why not, I also thought since im here on the gulf coast and ambient outside temps are mid 90's or higher that the moisture would boil out even it didn't quite get down to 28"hg.
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I have a friend who has that venturi style vacuum pump. It probably does draw down to 28" hg, but to get a good vacuum that will get all the moisture out, you will need to go for a deeper vacuum.
The gauges you are using are good for the purpose that you used them for, monitoring the level of refrigerant in your system.
The problem happens when you try to use the manifold gauges at the low end of the scale. The mechanism they use to cause the needle to deflect is just not sensitive enough to give you a good reading that will tell you if you are achieving the deep vacuum you need for your system to work properly, and to keep working for years to come.
The way the micron gauge works is that it has a tiny heating element and a tiny thermistor mounted near it. When there are molecules of gas present, they will carry heat away from the heater and the thermistor will read a cooler temperature which the display reflects as higher microns (not very deep vacuum)... when you approach a really deep vacuum, the molecules of gas aren't there to carry away the heat, and the thermistor starts reading hotter, which is reflected on the display as lower microns (a deeper vacuum).
I have seen various specifications as to how deep to pull a vacuum, but
here is a pretty good description of the procedure.
Your situation is that you are trusting your manifold gauges to tell you what vacuum you are getting. But you are trusting the
least accurate part of the gauge's range to give you the
most important information you need.
Here is
an interesting story from a working HVAC guy:
Quote:
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For years, I didn't know any better and just watched my gauges like I had seen everyone else doing, until I had some extra money in my pocket one day and seen a shiny new micron gauge right there in the display case. I bought it and tried it out the next day. I couldn't get that thing to pull down at all, but yet, my gauge was dead on 30 inches of vacuum. I worked and worked to get my gauges and hoses leak-tight and then realized my pump wasn't working correctly. I sent it in for repairs and things went much better after that, but I often wondered how long I had been hooking it up and doing nothing. That was probably 12 or so years ago and I have used a micron gauge since. Just two weeks ago, I had a system that wouldn't pull below 100,000 on my micron gauge. I kept at it until I found a tiny leak in the unit that I would have never even known was there without the micron gauge.
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I had virtually the same experience, with the exception that I was using a friend's vacuum pump which he had bought used off of ebay. He had serviced all of his family's car AC systems with it and was happy with it. He was still using the pump with the original oil it came with... he would let it pull down to 30 inches (no micron gauge), let it run for a couple of minutes, and call it good.
I borrowed it to set up a brand new mini-split I had bought. I did change the oil before I used it, and let it run for three hours before I closed everything up.
Later, I bought a new micron gauge and found that his pump, with new oil would barely pull down to 500 microns.
Two years later, my mini-split is still running just fine, but i really wish I had pulled a proper vacuum, using good working techniques.
After that experience, I bought a new HF two-stage vacuum pump and with fresh oil, it will go down to 60 microns which is great.
By the way, I relayed all this to my friend, and he now has his own micron gauge, and he changes vacuum pump oil every time he pulls a vacuum. He also rebuilt his vacuum pump.
So your situation is that you don't actually know how deep your venturi pump will actually go, and you can't trust a manifold gauge to tell you what you need to know because the low end of the dial is the least accurate part.
If you can find someone with a micron gauge, you would know for sure.
Or if you bought a new vacuum pump you would have a fair level of confidence that it would pull a good vacuum.
Quote:
Originally Posted by jroode32
The bad news is this morning after leaving the gauges on it all night, the pressure dropped about 100-PSI and when I turned it on it was still working but the LS stabilized @ 25-PSI and HS 150-PSI, I guess the leak could be in the gauges but I will definitely be do some leak testing today.
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This is where the soap bubbles come in.
So, I would say to keep working with the equipment you have and save up for a good vacuum pump. The HF two-stage is pretty good bang for the buck.
Regards,
-AC_Hacker