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Your 134 gauges will have that information on the face of the dial.
If you don't have a gauge set, you'll just be guessing.
 

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That's a big can of worms. It all depends. The gauges will just show you what the pressure is but you need to know what they should be. It varies depending on what type of refrigerant system it is. The pressure readings on an orifice tube system or an expansion valve or a VIR or any other style will all be different from each other. Then is it a serpentine condenser or a parallel flow or heaven forbid anyone still use an old tube and fin condenser. Tube and fin do not play well with 134a.


When I was an ASE master I was pretty good at it now I have forgotten most of it since I don't do it anymore. But roughly 50 and 250 @ 90*. I never liked doing AC work as there were so many junk rebuilt compressors that customers wanted to use because they were cheap... Four Siezens was the worst.
 

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With decent airflow through the condenser and the A/C set on "MAX", low fan speed, I'd expect to see 250-300 on the high side and 30-35 on the low side at 80-90*F.
 

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With decent airflow through the condenser and the A/C set on "MAX", low fan speed, I'd expect to see 250-300 on the high side and 30-35 on the low side at 80-90*F.

This is what I saw on my newly installed Classic Auto Air after putting in the exact amount of R134a required (24oz?). This after an overnight sitting with vacuum to make sure I had no leaks. I did run the vacuum pump for another 40 minutes right before the freon.


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This is what I saw on my newly installed Classic Auto Air after putting in the exact amount of R134a required (24oz?). This after an overnight sitting with vacuum to make sure I had no leaks. I did run the vacuum pump for another 40 minutes right before the freon.
Now that is some overkill there. It sure doesn't hurt anything to keep vacuumed down for that long, but generally you'll know if you have a leak in 15 minutes or so. Do these systems really take 24oz of 134? If so, that makes things really easy since it comes in 12oz cans. I'm used to systems taking something like 19.5oz, which is just a PITA for the DIY guy.
 

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Now that is some overkill there. It sure doesn't hurt anything to keep vacuumed down for that long, but generally you'll know if you have a leak in 15 minutes or so. Do these systems really take 24oz of 134? If so, that makes things really easy since it comes in 12oz cans. I'm used to systems taking something like 19.5oz, which is just a PITA for the DIY guy.

I was ready to break out the scale before I found out the spec on mine was 24oz. The only reason I left it overnight is it was midnight and I was beat so I charged it the following morning. I initially had one bad leak on a fitting I forgot to tighten. Once I snugged that one up it held vacuum. It was one of those moments of triumph during my project.


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