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Vacuum Pump Oil in Prius AC System?

I think that I might have accidently gotten vacuum pump oil in my 2005 Prius AC system when I was pumping it down before recharging it. I realize that this could be a big problem. Is it possible to completely flush the system? If so, how?

Background Info…

  • After installing a new condenser and pumping down the system for about 45 minutes, I am fairly certain that I completely turned off both of the valves on my manifold gauges before turning off the vacuum pump. I do wonder if I did not turn the valves completely off?

  • Shortly thereafter, I noticed what I think was oil in the manifold gauge’s sight glass. I immediately disconnected the yellow hose going into the manifold set from the vacuum pump. I would estimate that 1-2 oz of oil came out of the disconnected end of the yellow hose. I am fairly certian this oil is from the vacuum pump. Let me know if you think it was something else…

  • The vacuum did NOT hold on the system. I think this is because I either did not have the hoses connected to the system well or that I did not connect the condenser right–maybe one of the o-rings is not seated correctly or is damaged? I realize that I will need to work this out before recharging the system. I am prepared to troubleshoot this issue.

  • When I inspected the fittings on the blue and red hoses I did not detect any oil. Nor did I see any oil come out of the blue or red hoses connected to the manifold.

  • I am not sure that the vacuum pump oil went into the system, but I want to know how I can be assured of a clean system before I recharge it. Any help/guidance would be greatly appreciated.

What do you mean when you say the system did not hold vacuum? Did you vacuum the system for 30 minutes and then close the manifold valves and watch for vacuum decay? Did you ever achieve 30 inches of vacuum?

Also, when you assembled the system I assume you used the appropriate ND11 hybrid specific oil?

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Thanks for considering and thinking about my problem.

I pumped the system down to just this side of 30 inches of mercury–maybe to 28. As I understand it, this is about normal. The manifold gauges indicated that the system held that pressure for 45 minutes while the vacuum pump was running. After 45 minutes, I closed the high and low side valves on the manifold gauges. Then I turned off the vacuum pump. That is when I noticed the oil in the sight glass of the manifold gauges.

  • With the valves on the manifold set closed, I noticed that the system gradually lost pressure. I think that the gauge was reading 0 within 30 minutes.

  • I used a brand new set of gauges.

  • I have not intentionally added any new oil to the system yet. I was planning on adding about 2 oz of the proper hybrid specific oil to the system when I charged it.

If the system (with the gauge set closed) lost all vacuum within half an hour you’ve got a sizeable leak somewhere.

If you closed the valves before you turned off the vacuum pump you shouldn’t have gotten anything into the A/C system. But I would clean out the yellow hose before using it again.

If you didn’t add oil before you assembled the system how are you going to add it?

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If no oil was in the high or low hoses it is very unlikely that any leaked into the car’s system unless the vacuum pump was located above the level of the car’s fittings and the gauge/manifold was resting on the car. If you had the vacuum pump on the floor and the gauge set hanging from the underside of the hood it would be difficult for oil to feed upward and siphon the oil into the car. The vacuum pump likely has a leaking check valve though.

Thanks again for everyone’s comments and suggestions. It is a relief to hear that at least two people don’t think that I got vacuum pump oil into the ac system.

Here is more background information…

  • The vacuum pump was resting on a cinder block while the gauges were hung from the hood latch when I pumped down the system. The base of the pump was eight inches off the ground, which was lower than the entry points to the high and low sides of the system.

  • To add the oil to the system, I am planning to use something I found on called FJC 9148 Oil Charge ( This for hybrids including Prius AC units. One can has two ounces of oil and two ounces of R-134a. It gets fairly high reviews (4.5 stars out of 5). I have not used it yet.

why would you add more oil? It should have been added prior to installing the compressor (assuming factory specifications required it). At this point all it should need is refrigerants after evacuating the system…

I am NOT a pro, but, my understanding is that if I replaced the condenser, I needed to add 1.4 oz of oil to the system when I recharged it. My source is someone on the priuschat forum who quoted the repair manual. I think this is because not all of the oil makes it back to the compressor?

Here is the thread–>

Again, I greatly appreciate all of your help and guidance.

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I wanted to give an update. About a year after the repair, the ac is working fine. Last October, I found that I had a leak in one of the connections on my gauges by using dye. Once I tightened that down, I charged up the system and it has been working great for a year now. Thanks again for all of the help.

When did you realize the gauge fitting was leaking? 11 months ago?

Yes. I determined my gauge was leaking probably a week or so after my original post last fall. Sorry that my message was not more clear. Since this website was so helpful to me, I wanted to close out the story and hopefully help someone else who was fighting a similar problem.


We do appreciate getting the end of the story :slight_smile: It doesn’t happen as much as we’d like!