HVAC vacuum pump losing oil

[MushCreek]

I may have already figured out the mystery, but I want to see if anyone else has had this happen. I'm installing a mini-split, and bought a typical Chinese vacuum pump. I hooked it all up, and it seemed to **** it right down according to the cheap manifold gauge. I have a micron gauge on order, but just wanted to test it out. I pumped it down, and shut off the valve on the manifold good and tight. A half hour later, it was still holding vacuum. BUT- When I disconnected everything, the hose from the manifold to the pump was full of oil. At first, I couldn't figure out where all of the oil was coming from, but then I noticed that the sight glass on the pump was down near the minimum. My guess is this: The valve on the manifold is leaking, so the vacuum in the system pulled the oil out of the vacuum pump. Otherwise, I don't see how a pump pulling vacuum could blow oil into the hose. I'm not sure how I can test the manifold gauge, but I won't be using it after I get the micron gauge. I decided to get a valve core removal tool after watching some videos on the right way to do this.

 

[Gizzi]

I hope you didn't get a bunch of pump oil into the AC system. If you didn't isolate the pump from the system before shutting the pump off, the oil from the pump can migrate/travel into the system. Since the standing vacuum in the AC system is stronger than the pump without it running, there is nothing stopping the oil from siphoning out of the pump. Even with high quality pumps that can happen.

 

[MushCreek]

The thing that SHOULD prevent this is the shut-off valve on the manifold. Apparently it didn't. Luckily, the oil didn't get to the system. It doesn't appear to have gotten past the manifold, as the hose from the manifold to the mini-split was dry.

 

[Terry D]

I personally dont even use manifold gaugues when pulling a vacuum. I use a micron gauge and vacuum rated core removal tools

 

[rlitman]

The thing that SHOULD prevent this is the shut-off valve on the manifold. Apparently it didn't. Luckily, the oil didn't get to the system. It doesn't appear to have gotten past the manifold, as the hose from the manifold to the mini-split was dry.

The manifold valve should stop the vacuum in the system from pulling on the pump, but the hose is still evacuated.

 

[MushCreek]

So, I should have removed the hose from the pump to the manifold, or at least cracked it to release the vacuum? I guess the give in a rubber hose could continue to pull.

 

[Terry D]

Is this the first time you used the pump. Im thinking there is something wrong with your pump, possibly a check valve. I would wait till you get your micron gauge and vac it all down again with a different pump. Maybe even flush the lines

 

[chinboys]

I too had this problem with an Amazon, made in China vacuum pump, where it vomited its oil while pulling a vacuum.
You get what you pay for... threw it out after I purchased Yellow Jacket brand one. No oil issues and pulls a vacuum in no time.

 

[slow]

Is there not a valve on the vacuum pump? My Robinair 15600 has a valve on the side to shut off the vacuum pump from the gauge set.

 

[Dagny]

I know many disagree but I never leave any system in a vacuum . That is why I use a 4 valve manifold and have a can of refrigerant hooked up to it as soon as you have a good vacuum. Shut vac. valve open refrigerant valve.

If you have a leak the micron gauge should tell you. Also never shut the pump off under vacuum always valve it off break the vacuum the shut off.

 

[MushCreek]

No valve on the pump itself, just two different sized ports. I'm going to experiment, disconnecting the hose from the pump after pulling a vacuum. I really need the micron gauge, as the total vacuum scale on the manifold is only about 1/4" in travel. It seems to max out pretty quickly.

 

[Terry D]

My JB Industries pump does not have a valve. Just two different sized ports

 

[rlitman]

Is there not a valve on the vacuum pump? My Robinair 15600 has a valve on the side to shut off the vacuum pump from the gauge set.

That's a premium feature you pay for with a better pump. I just use hoses with valves on the ends.

 

[Gizzi]

I use an evacuation tee or manifold with ball valves on the end. Shut the ball valve off before turning the pump off and it won't siphon out of the pump into the manifold or system.

 

[MushCreek]

I got my micron gauge and hooked it up. The pump pulled it down quickly. I was careful not to leave vacuum on it with the pump off, and there was no oil in the hose, so the pump apparently is OK. Now I'm worried about the oil that got into the manifold. There's a sight glass on the front of the manifold, and I could see oil in there. I blew it out. What's the sight glass for?

 

[rlitman]

...What's the sight glass for?

It's to tell if you are charging with liquid or gas.

 

[Terry D]

I got my micron gauge and hooked it up. The pump pulled it down quickly. I was careful not to leave vacuum on it with the pump off, and there was no oil in the hose, so the pump apparently is OK. Now I'm worried about the oil that got into the manifold. There's a sight glass on the front of the manifold, and I could see oil in there. I blew it out. What's the sight glass for?

What do you mean " careful not to leave vacuum on it with the pump off" You should close the valves on the gauges before you turn the pump off. Is that what you did? You should not have oil in your sight glass, unless there was oil in your lines from the first time you did it. Is your oil level on your pump over full after the second evacuation. You may need to purge the lines out with nitrogen. I would not trust that pump.

 

[MushCreek]

The pump is fine. I screwed up by leaving it connected under vacuum, and the vacuum pulled the oil up into the hose, and apparently some got in the gauges, too. The hose from the gauge to the mini was dry inside. Further testing hasn't put any oil into the hoses, as long as I'm careful to disconnect everything. I do suspect that the shut-off on the manifold is leaking slightly. I think that's why it pulled oil out of the pump.

How do you purge the lines with nitrogen? I have a nitrogen regulator. There's only one access port on the mini-split, on the low pressure side. The high pressure doesn't have a port, so I don't see how to purge the lines unless I loosen a fitting, which I'd rather not do.

 

[Terry D]

The pump is fine. I screwed up by leaving it connected under vacuum, and the vacuum pulled the oil up into the hose, and apparently some got in the gauges, too. The hose from the gauge to the mini was dry inside. Further testing hasn't put any oil into the hoses, as long as I'm careful to disconnect everything. I do suspect that the shut-off on the manifold is leaking slightly. I think that's why it pulled oil out of the pump.

How do you purge the lines with nitrogen? I have a nitrogen regulator. There's only one access port on the mini-split, on the low pressure side. The high pressure doesn't have a port, so I don't see how to purge the lines unless I loosen a fitting, which I'd rather not do.

If you don't think oil got into the lines, then you should be ok. But yes, to purge with nitrogen, you would have to open the flare on the port without the Schrader out at the condenser. Then hook up the tank to the Schrader. How far did you pull a vacuum down on your gauge, hopefully to 200 microns. Then you close your manifold valve then shut your pump off. You should leave it set for about 15 min to see how much your micron gauge is going to rise. this is not checking for a leak, this is checking to see if all moisture, air and non condensables were evacuated. Shouldn't raise above 500 microns. Your micron gauge should be between your manifold and service port, preferably at the service port. You mini split book probably doesn't say it, but you should pressure test with nitrogen to check for leaks before evacuating. If you suspect you manifold is leaking, that would need to be repaired or replaced before doing anything

 

[metlmunchr]

The valve on the gauge manifold doesn't have to leak for oil to be pulled back into the hose. If the pump doesn't have a means of preventing backflow then the oil will simply flow back into the hose to fill the void created by the vacuum in the hose. That the OP found no oil in the hose going from manifold to the mini is indicative that the valve is not leaking.

Most vacuum pumps either have no backflow check valve or they have one that isn't very effective. The problem with trying to include an effective check valve is that such valves have a pressure drop characteristic that interferes with the ability of the pump to function efficiently. So, rather than using a poppet style check, the ones that use a check typically have a floating ball that moves to seal off the inlet and stop backflow. But, because of the low pressure differentials involved, these check balls don't tend to provide a reliable positive seal.

On large split systems where you may have a couple hundred feet of liquid and suction line, and want the pump to run for 24 hours or more prior to charging, it's common to have a normally closed electric solenoid valve connected to the pump inlet. Then, in case of a power failure while the pump is unattended, the solenoid closes and prevents oil backflowing from the pump into the system.

In the OP's case, what happened was normal, and can happen with name brand pumps like Robinair and J/B just the same as the imports since many of the known brands don't have backflow prevention either.

 

[MushCreek]

I'm going to pressure test the system with argon. I have a welding tank of argon, and from what I read, it's fine to use for pressure testing. A/C techs use nitrogen because it's cheaper, but I already have a welding bottle. I picked up a nitrogen regulator so I can have enough pressure.

I haven't done a full deep vacuum yet. I'm still waiting for the valve core tool I ordered. When I have everything I need, I'll first do a high pressure leak test, and if that's OK, then I'll vacuum it down for a good long time, then follow the procedure to open the refrigerant valve and replace the Schrader valve.

 

[Terry D]

I'm going to pressure test the system with argon. I have a welding tank of argon, and from what I read, it's fine to use for pressure testing. A/C techs use nitrogen because it's cheaper, but I already have a welding bottle. I picked up a nitrogen regulator so I can have enough pressure.

I haven't done a full deep vacuum yet. I'm still waiting for the valve core tool I ordered. When I have everything I need, I'll first do a high pressure leak test, and if that's OK, then I'll vacuum it down for a good long time, then follow the procedure to open the refrigerant valve and replace the Schrader valve.

This guy explains it very well. He has a lot of other videos also

 

[Terry D]

If you pump does not have a check or anti siphon valve built in, here is a kit that might work with yours. Without a check valve, even if your pump would lose power momentarily, it can siphon oil into the system

VPASU CPS Universal Anti-Siphon Valve Kit 1/4'' SAE, 3/8'' SAE & 1/2''-20 UNF

Universal Anti-Siphon Valve Kit 1/4' SAE, 3/8' SAE & 1/2'-20 UNF. Add to any brand of vacuum pump to prevent the cross-contamination of vacuum pump oil and the compressor oil of the system being serviced.

www.centurytool.net

 

[MushCreek]

I've watched that video. He does a good job of explaining it.