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How do you run a vacuum pump?

M-train on Sat March 31, 2012 2:21 PM User is offline

Its a Meirson super service 1/2hp unit {not a cheap China brand}.

First, I usually leave the little side lever just under the intake fittings {yellow hose in the pic} to the upright position 12-o-clock .

And, the ballast gas fitting on the pump closed when pulling a vacuum, is this correct? Also, when do you put the lever down to the close position {9-o-clock}?

Ok, Here is how I pull down an automotive system. Now we are talking about a new system with no refrigerant at all.

I first make sure each fitting is tight on the ac system, and the gauge manifold, etc.

Then I hook up the blue line of the AC gauges to the low side service port, then the red to the high side service port.

Then the middle hose, usually yellow hose, to the vacuum pump.

Before I use the pump I change the oil.

Now I open the hoses on the ac manifold gauge, and start the vac pump.

I'll let it run for about fifteen minutes until it gets down to 28" on the low side gauge. Then I turn off both the control knobs on the AC manifold, then the vac pump, and watch the low side gauge.

Is this the correct way to do this? I have just turned off the pump, and left the gauges open, but still I'm slowly loosing vacuum somewhere.

Today I tried checking the system with air from my compressor {the air is dry as I also use it for painting}, I couldn't find a leak using soapy water anywhere on the AC system.

So now I'm getting frustrated as to where the leak could be. I checked all of the new o-rings, and fittings, and even pulled the new evac core to pressure test it with no results. Everything seems to be sealing!!!!

So far I have a new evap core, new compressor, new expansion valve, all new hoses, and new receiver dryer. The only thing not new is the condenser.

mk378 on Sat March 31, 2012 3:26 PM User is offline

There's a leak somewhere in the car. Fill with air to about 100 psi, close both manifold valves, and watch for pressure drop. Do this first with the manifold not connected to the car and the hoses on the storage fittings to make sure your manifold and hoses don't leak. You could also put in few oz of R-134a and go over the car with an electronic leak detector. Do not mix R-134a with compressed air.

The isolation valve (black lever) on the vacuum pump should be closed whenever the pump is not running, especially if there is still a vacuum in the attached yellow hose. This prevents oil from being sucked out of the pump.

M-train on Sat March 31, 2012 4:17 PM User is offline

So you just leave the hose controls open, and the pump lever off when checking if the system is holding vacuum?

Thanks, I'm beginning to wonder if its the hoses as well.

Also, thanks for answering the question about the pump controls as I have looked a just about every youtube vid, as well as a net search with no luck. Everything I have found just skips over hooking up the pump, and goes right in to charging the system.

mk378 on Sat March 31, 2012 4:33 PM User is offline

You should close both, that way in case there is a leak in the yellow hose it won't mess up your test. Then if the vacuum seems to be holding, start the pump, open the isolation valve first to make sure the yellow hose is evacuated, then open both manifold valves again for the final evacuation.

M-train on Sat March 31, 2012 5:52 PM User is offline

OK, thanks.

One thing I just did was to take every hose off the AC gauges, and fill them with mineral oil.

Then I reattached them, and pulled a vacuum for about a hour. I turned off the lever on the pump {this was before I read your last reply}, and waited around for about thirty minutes, and checked the gauges again.

The both gauges hadn't moved so I'm now going to let the pump run over night {I will check it again, before bedtime just to make sure its holding}, and try to get my buddy who is certified over to install the R12.


Dougflas on Sun April 01, 2012 7:45 PM User is offline

Manifolds can leak at their valve stems. When you pressurize the system squirt bubble search on them to insure no leakage. The ballast valve should be open when first starting to pull a vacuum. After the compound guage doesn't move any more, then close the valve. When I change my pump oil, I run the pump a few minutes and then change the oil. By the way, the hoses you are using are not "vacuum rated". Vacuum rated hoses are black in color and heavier. One more thing, put Nylog at all of your hose connections. zit seals better and also makes the hose gaskets last longer.

M-train on Mon April 02, 2012 3:17 PM User is offline

Well, that was apparently the problem. The hoses, even though they didn't blow bubbles with soap, they were still part of the leak.

I turned the lever down on on the pump, and closed the manifold gauges, and it held vac till yesterday morning when I did a check.

I got the refrigerant put in, and now it blows cold. There was a small panic time when I ran out of gas, and had to run to the gas station for more gas.

Thanks again for all of the info on the, "ballast plug", and pump lever. I scanned the net everywhere about how to operate the pump without luck.

Thanks again.

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