It could be that the pump you rented this time was inadequate. Or, you might have had a leak somewhere in your manifold gauge set hook-ups. A small system leak is also a possibility.PromiseRing wrote:I had vacuumed the system for about 1 hour or maybe 1.5 hours with a vacuum pump I rented from AutoZone. This is the same type I’ve rented there many times before and have always been able to achieve 29-almost 30 in Hg on other vehicles (Including her Toyota, before the new system). Considering I had removed every single possible connection in the system, the likelihood of a leak is higher. When I vacuumed it for 1-1.5 hours, it was 10pm and she was leaving the next morning for the airport, so I was in a hurry to get some refrigerant in the system.
Hopefully not, but let us know whether it stops cooling.PromiseRing wrote:If she reports back that the ac stopped working, I can only assume it’s because of a slow leak. Now that I think about it though, since the system was open for a few hours, isn’t it much more difficult to get that 29-30 in Hg? On a system that hasn’t been exposed to outside air, it seems to go into vacuum much easier. I’m wondering if I did a longer vacuum and achieved that number, if vent temps would be cooler.
Non-condensable gases (air and moisture) in the system will affect cooling. How much depends on the amount. Less than one percent probably won't be noticeable.
I don't think it makes much difference whether the system has been open for a while. A good vacuum pump should pull down to 29 InHg or better almost immediately. It's just that you have to maintain that level of vacuum for at least 30 minutes to boil-off all the air and moisture. I like to evacuate for one hour or more, as you did. Sometimes, you'll have a bit of internal out-gassing in a well-sealed system that will cause the vacuum reading to drop a little after the initial evacuation. But achieving only 26 InHg on the first attempt indicates a problem someplace. If you have significant non-condensables in the system due to inadequate evacuation, cooling will be compromised to some extent as already mentioned. A system running with significant non-condensables will usually have higher than normal high-side pressures even though airflow over the condenser is sufficient.
On this system, it sounds like the airflow is as good as it's going to get.