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Using an Ac Vacuum Pump, Having Issues

Just have a general question about ac vacuum pumps. I tried to use one the other day for the first time, and couldn’t figure out how to get the pump itself to hold pressure.

  • First I got a junky parts store rental pump and followed instructions to check oil.
  1. Block off suction port, let run and check oil level
  2. Slowly add oil as necessary

As soon as I turned it on, freon started blowing out of the oil pour cap, so i tightened it down and tried again. Same result. So I figure it’s just a shot pump and bring it back. They swap it out for a new in box unit and I bring it back and the same exact thing happens (but with just air this time.) Am I just having bad luck or is this normal?

Is the AC system you’re connecting the vacuum pump to void of refrigerant?

Tester

Need more info.

Didn’t even make it to that point. I was just test running the pumps per instructions and number one blew freon from the oil cap and number two blew air since it was new and unused prior.

What more info? That’s all that happened.

Are you saying the AC system still has refrigerant in it?

Tester

When you write: “I tried to use one the other day for the first time, and couldn’t figure out how to get the pump itself to hold pressure”, what exactly did you do other than “tried to use one the other day” that resulted in the pump not holding pressure?

This is from my original post

" * First I got a junky parts store rental pump and followed instructions to check oil.

  1. Block off suction port, let run and check oil level
  2. Slowly add oil as necessary

As soon as I turned it on, freon started blowing out of the oil pour cap, so i tightened it down and tried again. Same result. So I figure it’s just a shot pump and bring it back. They swap it out for a new in box unit and I bring it back and the same exact thing happens (but with just air this time.) Am I just having bad luck or is this normal?"

Yes it does, but I didn’t make it that far. I was just adding oil/testing the pump prior to hook up.

So?

Are going to repay the parts store for the vacuum pumps you ruined?

I can believe it!

I’m roaring my ass off!

Tester

So you’re not supposed to turn them on?

Not with refrigerant in the system!

Tester

I’m pretty sure you don’t understand me. The instructions say to test run the unit (without being hooked up) to circulate and check oil levels. So they weren’t even hooked up to a vehicle or cooling system. Simply plugged into an outlet.

No!

I totally understand you.

And everything you’ve stated so far has nothing to do with normal AC service or expectations.

Tester

Did you hook it up to your AC system when “freon started blowing out of the oil pour cap”? If not, where did the freon come from that blew out of the oil pour cap?

So you don’t understand. My question was specifically about ac vacuum pumps, nothing to do with servicing an ac system.

Just like if I asked “Why does my floor jack keep falling down even when in the tightened position with no weight?”

And you ask “Well how much does the car weigh?”

No I didn’t even make it past oiling/test starting the unit solo/ unhooked from anything. I assume it was freon, it was a cold rising gas.

The oil also had a green tint in the sight glass if that helps.

There is no refrigerant in a vacuum pump, if the pump was stored upside-down you might see a mist of oil discharged from the exhaust vent but that doesn’t indicate failure.

So if you didn’t connect to an ac system, and were just checking the ac vacuum pump, where did the freon come from?