Automotive Air Conditioning Information Forum

I am stumped right now. I have a 2015 Nissan Sentra SV. I hooked up gauges to low side and high side. Low side was too high, about 60. High side was correct pressure. I recovered some of the refrigerant to the correct psi based on the ambient temperatures. The air was blowing hot. Then i added it back to 60 and now its cold again. Anyone know why this would be the case? I have the max ac on and its still not getting as cold as i'd like.

Pressures are an effective diagnostic tool but can't tell us how much refrigerant a system contains. The only way to do that is to weigh the charge into a system that's under a well-held vacuum.

According to the specs I have, your car takes 17.6 ounces net weight of R-134a and 3.0 fluid ounces of PAG-46.

Weigh it on a scale? I rented one of those vacuums from autozone. How would I weigh the refrigerant already in the system? And why does every video on the internet use the pressure gauge on the can to fill it?

I've never seen a pressure gauge on anything other than those Wonder cans they sell at parts stores. Real Guage set, cylinder of refrigerant, and a scale. As for how much a system has in it. Professional machines can reclaim the refrigerant and show how much was removed. I've yet to see a formula calculating the proper amount of refrigerant in a system by pressure.

kevboost wrote: ↑Sat Jul 29, 2023 12:24 pm How would I weigh the refrigerant already in the system?

You would have to recover whatever refrigerant is already in the system (if any) using a professional RRR (Recover, Recycle, Recharge) machine, which will tell you the weight of the refrigerant removed, along with the fluid ounces of oil removed. Then, you would recharge the system according to the exact weight-of-charge the system calls for while adding back the same amount of oil. Yes, very accurate refrigerant scales are also used together with a Manifold Gauge Set and refrigerant source—e.g., a 30-pound cylinder—to properly recharge a system. Charging or recharging by weight is the only correct way to do the job. Pressures alone simply cannot tell you how much refrigerant a system contains.

kevboost wrote: ↑Sat Jul 29, 2023 12:24 pm And why does every video on the internet use the pressure gauge on the can to fill it?

With all due respect, you came on this Forum, which comprises a small group of trained MVAC professionals, retired pros, and knowledgeable others, for advice on how to properly recharge your system. We offered you our best opinion about what should be done to address your issue. Just because you see videos on the Internet doesn't mean it's the correct way to charge a system. But you already found that out. Go to any professional MVAC shop in your area and ask about charging using one of those Miracles In A Can and see what kind of answer you get. We can only offer you our best professional advice. What you do with that information is up to you.

kevboost wrote: ↑Fri Jul 28, 2023 3:17 pm I am stumped right now. I have a 2015 Nissan Sentra SV. I hooked up gauges to low side and high side. Low side was too high, about 60. High side was correct pressure. I recovered some of the refrigerant to the correct psi based on the ambient temperatures. The air was blowing hot. Then i added it back to 60 and now its cold again. Anyone know why this would be the case? I have the max ac on and its still not getting as cold as i'd like.

My brother had a 2014 and not knowing any better shot additional refrigerant into it. It would not cool with the proper charge and low side pressures were high and high side pressures were low. The problem ended up being a failed compressor control solenoid. A $25 part that Nissan wants to sell to you as a complete compressor assembly. I was able to find a solenoid replacement through the aftermarket. I recovered the refrigerant, replaced the solenoid (the compressor itself does not even have to be removed) vacuumed and recharged the unit and the a/c went back to its old marginally performing self. From day one that car only had good cooling when you were off the throttle. As soon as you put your foot on the throttle the airflow went to about half capacity and the a/c compressor would cut capacity. It is built into the electronics to optimize fuel economy by reducing engine load. Might have been specific to the 6spd manual cars, but I doubt it. On throttle, slower blower speed, less compressor, coasting in gear at higher speed, more airflow and more compressor action. Terrible design for Texas heat atleast. I have never experienced another vehicle that would reduce the ac output in extreme heat under light throttle operation.

I will also caution you on those Sentras. The compressor bolts are prone to breaking off in the oil pan. The only replacement oil pan available will be used. Nissan in their infinite wisdom sells a replacement pan for an upgraded newer engine setup. IIRC, have to change the timing cover, timing set, and oil pump to retrofit the new oil pan to the older engine. The oil pan part number for those cars Service Files in the parts catalog and gives you a laundry list of parts to buy and replace on the actual engine in order to replace the pan.

Hello,

I'd like to revive this thread a little bit as I'm having a similar, but not exact issue on a 2006 Mazda3.

Question, if a system had the adequate refrigerant amount within its specifications, wouldn't it be able to attain the proper pressures in the proper ranges? I.E. proper pressures= proper refrigerant charge?

Or is the idea here that if the system has the proper amount of refrigerant in it by weight; if the pressures are not in range then there is an issue somewhere?

Thank you.

mizzle33 wrote: ↑Thu Jul 04, 2024 8:39 pm Hello,

I'd like to revive this thread a little bit as I'm having a similar, but not exact issue on a 2006 Mazda3.

Question, if a system had the adequate refrigerant amount within its specifications, wouldn't it be able to attain the proper pressures in the proper ranges? I.E. proper pressures= proper refrigerant charge?

Or is the idea here that if the system has the proper amount of refrigerant in it by weight; if the pressures are not in range then there is an issue somewhere?

Thank you.

It's best to start your thread and not tagging into another.

Thanks, will do....