Automotive Air Conditioning Information Forum

I vacuumed it 15 minutes and let it sit another 15. Gauge steady at -30. Connected a micron gauge and after 15 more minutes it's at 460 microns. Will let it vacuum another half hour and let it sit an additional half hour and check the micron reading. Is that long enough or should I wait until the morning?

atikovi wrote: Thu Oct 22, 2026 3:52 pm I vacuumed it 15 minutes and let it sit another 15. Gauge steady at -30. Connected a micron gauge and after 15 more minutes it's at 460 microns. Will let it vacuum another half hour and let it sit an additional half hour and check the micron reading. Is that long enough or should I wait until the morning?

Did the refrigerant leak out, is that the reason for evacuating the system? If so, I recommend replacing the desiccant element, as well as the cabin air filter.

Bear in mind that the system can hold and maintain a vacuum, but still leak under pressure. One-half hour should be sufficient to determine whether the vacuum holds.

The specs for this vehicle are 16.0 ounces net weight of R-1234yf, and 4.4 fluid ounces of PAG-46 intended for the aforementioned refrigerant, or whatever specs are listed on the under-hood decal (the decal takes precedence).

12 hours later it's at 350 microns at 45°. I could put in half a charge and check it in a week or two.

350μm is very good, but doing MVAC work at only 45°F is difficult. It's hard to test and charge a system at that low of an ambient. Better to wait until the ambient temperatures rise to a minimum of 80°F, or work in a heated environment—easier said than done, I know.

An alternative is to heat the small cans with warm water (not a torch), or if using a 30-pound cylinder, warm it with an electric blanket specifically designed for that purpose.

In the meantime, you certainly could give the system a half charge, and then check for leaks later on using a "sniffer."

Ended up putting a full charge in. $45 of 1234. Doubt it will be near 80 again this year.

That refrigerant is expensive! Did the R-1234yf leak out?

Even in my area, it's only in the high 60's to low 70's during the day.

I don't know. It was 0 when I checked so expected to see something obvious, but saw nothing.

atikovi wrote: Fri Oct 23, 2026 12:25 pm I don't know. It was 0 when I checked so expected to see something obvious, but saw nothing.

Are you the original owner? If not, then the system has a leak (or leaks), or a previous owner recovered the refrigerant with the intention of finding the leak. Maybe that person didn't find it, or maybe she/he found the leak, repaired it, then didn't get around to the evacuation and recharge process. If you don't know the vehicle's service history, almost anything is possible.

Nope just got it.

In that case, if you have a garage, preferably heated, pull it in there and check the system for leaks. Pay particular attention to the compressor shaft seal and the condensate coming from the evaporator. If the evaporator is leaking, the condensate usually will contain UV dye if you did add it when you recharged the system. You'll need a special flashlight and glasses for the UV dye to show up in a dark garage. And you'll also need a "sniffer."