Automotive Air Conditioning Information Forum

JohnHere wrote: ↑Thu Aug 11, 2022 12:37 pm If you flush the evaporator in situ, try to ensure that you get out all of the flushing chemical, which will cause problems if you inadvertently leave any of it in there.

Thanks. Hopefully we can.

Blow it out thoroughly and repeatedly, preferably with nitrogen. Because the evaporator is designed as a low-pressure component, I use no more pressure than 100 PSI to be on the safe side. Lacking a nitrogen set-up, you'll have no choice but to use shop air—the dryer and more filtered, the better.

JohnHere wrote: ↑Fri Aug 12, 2022 8:52 am Blow it out thoroughly and repeatedly, preferably with nitrogen. Because the evaporator is designed as a low-pressure component, I use no more pressure than 100 PSI to be on the safe side. Lacking a nitrogen set-up, you'll have no choice but to use shop air—the dryer and more filtered, the better.

He only has shop air and no nitrogen set up so that is going to have to work. I used shop air years ago when I converted one of my 92 Cavaliers from R12 to R134a and it worked fine for years until the compressor seal leaked.

Thanks for the pressure recommendation.

Then get a super low vacuum for several hours

Latest update: AC seems to be fixed. The owner got everything flushed and put back together and dried out with filtered shop air. He brought it over and I put the vacuum pump on it and vacuumed it down for 30 minutes and let it sit for 30 minutes. Gauges never dropped at all during the 30 minutes. I turned on the pump and let it go another 15 minutes and then let it sit for another 15 minutes. Gauges again never dropped at all.

I charged it with 45 ounces of refrigerant. Vent temps at idle were 48 to 50 degrees with outside temps around 87 and very humid. Pressures at idle were 32 low and about 175-180 high. At around 1500-1800 rpms they were 35-36 low side and around 300-325 high side. He took it for a drive and temps went down to around 46 degrees. The AC was on Max and highest blower speed the entire time during the charging and test drive.

He had also replaced the cycling switch and high pressure switch with new Motorcraft ones. He is happy with the performance so hopefully everything lasts awhile though he is talking about selling the truck.

Thanks again for everyone's help. I really appreciate it.

Glad it is working but the system is wet.
No where near sufficient vacuum time

tbirdtbird wrote: ↑Fri Aug 12, 2022 6:24 pm Glad it is working but the system is wet.
No where near sufficient vacuum time

Well, unfortunately I did not see your post about vacuuming for several hours until after I had done the job. He is happy with the performance and actually thinks it's too cold so I guess the next time I run into this, I will vacuum for longer.

The vacuum never did decay at all on the gauge which was right at the 30 mark on the vacuum side so I figured that there was not any moisture left in the system. Other systems that I've done in the past that had moisture in it, the vacuum would drop on the initial vacuum because it boiled off the moisture and then would stay solid after the next vaccum down.

Just for the record, a vac time of 30 min is never enough.
Moisture will not boil off until 29.9, and once you hit that number, it takes time to get all the water vapor out. Not sure why people rush this important step.

The better the vac the better the system will run, and the longer it will run, durability wise. Water vapor combines with the refrigerants and forms acids, which harm the compressor parts.

A shop may rush a vac because they want you in and out, but a private concern can afford the additional time

tbirdtbird wrote: ↑Fri Aug 12, 2022 8:44 pm Just for the record, a vac time of 30 min is never enough.
Moisture will not boil off until 29.9, and once you hit that number, it takes time to get all the water vapor out. Not sure why people rush this important step.

The better the vac the better the system will run, and the longer it will run, durability wise. Water vapor combines with the refrigerants and forms acids, which harm the compressor parts.

A shop may rush a vac because they want you in and out, but a private concern can afford the additional time

It's interesting that you say that 30 minutes is never enough time to vacuum down a system because when I first came to this forum back in 2006 and was asking advice on how to repair and recharge the system in my 92 Cavalier, I was told by several people at the time to vacuum for at least 30 minutes and if it held for 30 minutes, you were good to go ahead and charge. The repair of that Cavalier lasted 10 years before the compressor developed a leak and lost the charge.

Since that time, I've always done 30 minutes, let it sit for 30 minutes, vacuum again for 15-30 minutes and then let it sit an equal amount of time and if the pressures hold, I charge. On this truck today I did a total of 45 minutes.

I own a 98 Chevy K1500 truck that I bought new. In 2007 I replaced all of the AC components in the truck and vacuumed the system as I described above and 15 years later it still blows ice cold so my procedure definitely didn't hurt the system durability wise. It's lasted longer so far than the original charge and compressor did.
In 2007 I bought a used 98 Chevy K3500. In 2010 I replaced all of the AC components and followed the same procedure and 12 years later it's still blowing ice cold.

I have a 6 cfm Robinair vacuum pump so it pulls the system down to the 29.9 pretty quick and I'm not waiting very long before it starts boiling the moisture out.

With all of that being said, what is your minimum recommendation for how long you should vacuum a system down for?

I forgot to mention that Tim, a moderator here posted this viewtopic.php?f=4&t=13603 information in the AC procedures forum which was updated in 2020 because it's basically the same info I printed out in 2006 when I first joined and he states that 30 minutes of evacuation is usually enough.