Today I serviced my ac with a can of r134 on my 98 maxima. The gauge did read on the red mark, but the ac was working at 90 degrees before I added the can. I still put some. I added the whole can. About 12oz. The ac was very good. I shut the car off for 10 mins to get ready for a test drive. I go back in and start to drive to the bank and the compressor wouldn't turn until I arrived to the bank. Then I further test drove it and the ac went all the way to 59 degrees, it would never go there in this heat (today is 112 degrees) it usually stayed at 75. But then at 2500 and up rpm I hear a noise. It doesn't do it at anything lower than that. If it's overcharged how do I release pressure? Through the low pressure hose? I don't get how its high pressure when the damn car was not even blowing cold ac. If the weather is over 85 it said to move the dial to 85 plus degrees on the valve. The needle was just a little past it on red. The needle gauge is wrong when it's not on, it reads 10psi and it's not connected to the low pressure hose. When I filled it it was at 70

 

How about take the car to a local shop, have them check and adjust your pressures.

Did you have a leak?

Did you loose PAG?

Did you add any PAG?

Do have the correct volume of PAG in the system?

Did you truly add R134 or did you use one of those AC Doctor/AC Pro concoctions that contain just about everything except R134?

 

Could be your compressor clutch is sticking and wasn't engaging properly. Overcharging can build high pressure the hotter it is outside which could cause a leak at the weakest point. When charging the gauge could show pressure a little high but probably won't give you a proper reading until the compressor engages allowing you to fully charge the system. You should have a sticker on the firewall or under the hood showing the refridgerant capacity for your car. If you started with no refridgerant and had a leak you could have had air and moisture in the system which when mixed with refridgerant will throw off the reading and could also cause the refridgerant to be acidic. I know it can eat away and cause leaks with copper lines but not sure about the aluminum lines in automotive systems. The system should be vacumed before charging. You could also have a shop pressurize the system with nitrogen to see if it holds pressure but the refridgerant probably also has a green dye which can help detect leaks.

 

The noise went away and pressure already dropped to like 59 psi

 

However the noise comes and goes then the compressor wouldn't turn on until I drive or restart car sometimes. Now the pressure is at 40 it dropped alot. Take it to the shop? It does like a high motor noise kinda like a buzz or grind