Bringing up A/C pressure from a vacuum to trick it into turning on?

ERNESTO36021

MEMBER
2014 NISSAN ALTIMA
2.5L
AUTOMATIC
200,000 MILES

Hello, I just watched a video from August 2020 titled, "How to Vacuum Down and Recharge Your A/C System! - EASY". In that video you state "So the AC system, if you turn the truck on right now the AC compressor isn't going to click on, nothing's going to work the pressure switches aren't going to be active, because it thinks the systems empty which it is, so it's not going to work to protect itself. So, you need to bring up that pressure enough to trick the system into working and that is right about where the keg pressure is." My question is, if I'm not using a keg to recharge the system, instead I'll be using the little cans. Do the cans have enough pressure to bring the pressure of the system high enough to trick the system into working? Also, if my car requires 1.15lbs of refrigerant 18oz roughly. And each can only contains 14oz could I just use the second once the first is empty? Like it would be ok to just unplug the empty one and plug in the new one? One last question I'm replacing the AC compressor valve. Would the steps be 1. Evacuate the refrigerant 2. Replace the air compressor valve 3. Vacuum the system 4. Add new refrigerant? Thank you for taking the time to read and answer, I'm a beginner so I really appreciate this.

1 Reply

STEVE W.

MECHANIC
12,961 POSTS

Your steps are correct. Use a machine to pull the charge out, do the repairs, test for leaks, vacuum the system down then recharge.
As for tricking the compressor, you want to set the can in hot water with both on a scale so you can measure the amount. Note the start weight. Then open the valve and let it fill the system with that can. When it shows the can is empty and it was actually 14 OZ. Have the engine running and AC on max, the compressor with kick on as soon as the pressure is high enough that it thinks it has a charge. Now once that can is empty, close the valve and then change the can out and set the new can on a scale that reads ounces and start charging until you have put in the required charge.