AC question: pull vacuum on service hoses before connecting?

[CDX825]

You should always purge your hoses out. Air in any type of refrigeration system is bad. When you connect your gauges to a system with pressure on it you should crack the hoses loose at the gauges for a second or two in order to push the air out of the hoses. You should be doing the same thing when you connect a can of refrigerant to the center hose on your manifold gauge set.

 

[Nukeman7]

I just hooked gauges up to the system and get a reading of 38 psi on both gauges showing it is equalized. Note - It was about 56F outside. According to the F R134a blue scale on the gauge 38 psi corresponds to about 44 F. When I made this measurement it was about 56 outside.

The compressor shuts off when the is refrigerant pressure too low (< 2.0 bar). 2 bar = 19 psi. So at 38 pis I am above that. So I guess this is not what is keeping the compressor from running.

If the G65 pressure sensor is defective as I suggested in Post #15, it would not be able to detect that it is above 19 psi. Hence, a defective G65 transducer would not send the proper signal to the ECU to energize the compressor.

 

[tiredguy]

If the G65 pressure sensor is defective as I suggested in Post #15, it would not be able to detect that it is above 19 psi. Hence, a defective G65 transducer would not send the proper signal to the ECU to energize the compressor.

thanks , good point. I was thinking that G65 just interrupts the compressor operation when the pressure exceeds a certain value. Is G65 dynamic where it works across the pressures or does it just act as a switch?

 

[Nukeman7]

thanks , good point. I was thinking that G65 just interrupts the compressor operation when the pressure exceeds a certain value. Is G65 dynamic where it works across the pressures or does it just act as a switch?

Got this info from Google AI: The G65 sensor (officially called the A/C Refrigerant High-Pressure Sensor) is a critical 3-pin electronic sensor in Audi and Volkswagen air conditioning systems. Instead of a physical on/off switch, it uses a silicon crystal to constantly measure refrigerant pressure and sends a pulse-width modulated (PWM) signal to the car's computer.

The following video explains how to test it if you are adventurous...however, I'd just replace it with the $12 part.