'92 Tercel R12 A/C pressure readings

[MacG467]

Hey everyone. N00b here.

My father and I fixed a leak in the Schrader valve on the high side A/C line and now we need to charge the system.

My father's R12 certified (he works on centrifuges), and has all the correct equipment and a 30lb bottle of R12.

We realize that the best way to put R12 in is by weight (the car even says to put in between 1.54 and 1.76 lbs), but we don't have a scale to use.

We were both wondering what the low side and high side pressure readings should be between with a full charge instead of using weight. Centrifuges go by pressure and not weight, so he wasn't prepared to require a scale.

Also, when he pulled a vaccuum, he could only manage pulling down to 150 microns after two hours of vaccuum. He's normally accustomed to pulling 50 for the centrifuges he works on. Is 150 acceptable?

Thanks for the info,
-MacG467

[96paseo]

Originally Posted by MacG467

Hey everyone. N00b here.

My father and I fixed a leak in the Schrader valve on the high side A/C line and now we need to charge the system.

My father's R12 certified (he works on centrifuges), and has all the correct equipment and a 30lb bottle of R12.

We realize that the best way to put R12 in is by weight (the car even says to put in between 1.54 and 1.76 lbs), but we don't have a scale to use.

We were both wondering what the low side and high side pressure readings should be between with a full charge instead of using weight. Centrifuges go by pressure and not weight, so he wasn't prepared to require a scale.

Also, when he pulled a vaccuum, he could only manage pulling down to 150 microns after two hours of vaccuum. He's normally accustomed to pulling 50 for the centrifuges he works on. Is 150 acceptable?

Thanks for the info,
-MacG467

Pulling vacuum down to 150 is alright for a car. The most important part is to do the "standing test" after pulling the vacuum. Section 609 standards specify 24 hours standing vacuum and re-check to ensure no leaks are present. I'm not saying you have to do this but give it at least 2 hours and check the gauge to see if your losing vacuum. The two biggest things you'll be fighting with an older system are 1)worn out compressor shaft seal and 2)o-rings at the unions are probably in need of replacement. As far as charging goes, normal operating pressure ranges are as follows. Low side 30-40 psi and high side 185-200 psi. These are subject to change based on engine rpm so don't overcharge. After you get the system running, bring the engine rpm up to 2500-3000 rpm, this is typical cruising range for most drivers. Your low side pressure will drop but make sure the compressor isn't trying to pull a vacuum. Your low on charge if the pressure gets below 15 psi. If you have a bathroom scale handy, you can charge by weight. No need for a special scale just watch your pressures as you go, stop feeding refridgerant and check the scale. I would certainly recommend replacing all o-rings at the unions as well as the dessicant drier/filter on the side of the condenser. Those parts can be had for cheap from rockauto.com Good luck. Feel free to PM me or post a reply if you need more information.

[MacG467]

96paseo,

Thank you very much for your insight! Unfortunately, we already put R12 in the system. With your extra info, I can now determine that we didn't put enough in and we'll be adjusting it next weekend. The compressor cycles, but the air coming out of the vents isn't very cold. We probaby filled the system at about 1200RPM instead of your recommended 2000-3000.

As far as replacing certain parts is concerned, I'm having my wife check to see if the A/C performance degrades over the week. If so, we'll know more problems are afoot.

The Schrader valve on the high side was missing the cap and caused the entire valve (including the tube) to corrode. After we replaced the valve and pressurized the system, we had to quickly put a cap on and run a leak detector around it. Fortunately, there was no leak. I'm not about to pay a professional to sweat on another valve assembly if I can just cap it and get no leaks.

That, along with some of the stories my father told me about his experiences working on centrifuges made for an enjoyable morning.

Thanks again! And I think I'll stick around here for while.

[96paseo]

Originally Posted by MacG467

96paseo,

Thank you very much for your insight! Unfortunately, we already put R12 in the system. With your extra info, I can now determine that we didn't put enough in and we'll be adjusting it next weekend. The compressor cycles, but the air coming out of the vents isn't very cold. We probaby filled the system at about 1200RPM instead of your recommended 2000-3000.

As far as replacing certain parts is concerned, I'm having my wife check to see if the A/C performance degrades over the week. If so, we'll know more problems are afoot.

The Schrader valve on the high side was missing the cap and caused the entire valve (including the tube) to corrode. After we replaced the valve and pressurized the system, we had to quickly put a cap on and run a leak detector around it. Fortunately, there was no leak. I'm not about to pay a professional to sweat on another valve assembly if I can just cap it and get no leaks.

That, along with some of the stories my father told me about his experiences working on centrifuges made for an enjoyable morning.

Thanks again! And I think I'll stick around here for while.

Certainley sweating a new valve isn't necessary. Unless there is a break in the pipe, you shouldn't be concerned. I've never seen sweating needed on a car. Toyota uses unions exclusively. Charging at normal idle 1200RPM is ok. Sorry if I didn't make that clear before. Just by running the A/C, your idle should rise to near that mark. R12 is the best. I'm suprised that you have access to it. R414B and R-12 work nearly the same. Check into the pressure/temperature chart for refridgerants. You will find that R-12, R-134a and R-414B have the same P/T properties. Most importantly that the temp and pressure relationship are the almost same. Good luck.