Evacuating Procedure, Thumb Knobs on Gauge

[duke16]

I bought a set of Harborfrieght gauges and a ventrilo-type pump. The pumpis hooked up to my compressor and then to the yellow port on the gauges. High and low side are connected. But here's where I get a little confused. Do I open the thumb knobs on the gauges to evacuate? Or do they remain closed? I have the control valves on both the low and high side open. Just not sure about these thumb knobs.

Thanks.

Air Vacuum Pump, Ventrilo Style
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=96677

A/C Manifold Gauge Set
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92649

 

[duke16]

I think I figured it out. I guess the thumb gauges are supposed to both be open, but what I was doing wrong was actually the control valves. In the instructions for the gauges it said clockwise to close, I misintreptted what that meant. I figured I wanted to start the comrpessor, and then turn the control valves counter-clockwise to open the flow. But that was wrong.

Anyway, it looks like I have a leak. As soon as I turn my compressor off, the pressure starts building back up again (i.e the vacuum goes away). I tried some of the U.V leak detector stuff, but I can't locate the leak. Not sure where to go from here.

 

[Cobraguy]

Put a partial charge in it and check it with a leak detector. If you don't have one, then I would suggest taking it to a shop that does. They will find it for you.

 

[duke16]

About how many cans would it take to create enough pressure for the compressor to kick in?

 

[Cobraguy]

It might start trying to cycle after 12 oz. But you don't need it to engage to find your leak. One can...maybe less...should show the leak. And if you have the fluorescent dye in the oil, then you might find it without a partial charge.

 

[duke16]

Well it's possible I just damaged my compressor. I got a can of Prestone 134a +UV Dye and on it is says "Use only with this end up - Liquid Charge Only" and an arrow pointing to the bottom. So I assumed that meant hold the can upside down. So I attached it to my gauges and opened up the high side. Once it wouldn't pull any more, I closed the high side and opened up the low side and turned the engine on. But this entire time the can was upside down. The can also says that the system should be liquid charged only, whatever that means. And that the liquid refrigerant should not be charged to the low side without passing through a throttling device, again, not sure what that means. I hope the gauges count as a "throttling device", otherwise I have no idea.

 

[Cobraguy]

There are a lot of vehicles charged with the cans like you say. Remember...you're dumping the liquid into the accumulator before it ever gets near the compressor. I wouldn't be the least bit worried about it. But I'm going to give you some unsolicited advice. Never, and I mean NEVER EVER charge through the high side port. Even with the engine off. It's a horrible habit. If you should happen to forget to close that high side valve and run the system, you will introduce very high pressures to the can. BOOM.....

 

[duke16]

Ah, well that's good then. Thanks.

Looks like my leak is the pipe going into the compressor. Am I going to have to wait for everything to slowly leak back out now before I can repair the leak? I don't really have anyway of collecting the stuff I just put into the system.

 

[Cobraguy]

Well, legally, it needs to be recovered.

 

[KPT]

I have a real vacuum pump (Robinair 4 CFM) and I am in Apex. You're welcome to come use it, its about $5 for vacuum oil for it (I change the oil every time I use it). Or stop by my favorite brewery in Holly Springs (Carolina Brewing Company) and grab a 5 gallon keg....

I have those same gauges and never touched what you are calling the control gauges. They will open the high/low valves and hold the refrigerant in the lines in the closed position.

 

[Cobraguy]

You change vacuum oil every time???

 

[duke16]

I have a real vacuum pump (Robinair 4 CFM) and I am in Apex. You're welcome to come use it, its about $5 for vacuum oil for it (I change the oil every time I use it). Or stop by my favorite brewery in Holly Springs (Carolina Brewing Company) and grab a 5 gallon keg....

I have those same gauges and never touched what you are calling the control gauges. They will open the high/low valves and hold the refrigerant in the lines in the closed position.

Thanks for the offer, if I hadn't already put one can in I would taken you up. But I just went ahead and filled the system with another 2 cans to be done with it.

The leak doesn't appear to be too big, this should get me through the rest of summer at least.