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.

 

[wtd]

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.

Have you tested the wiring down to the compressor to see if you are getting power to it? Have you tried jumping the AC relay to see if your clutch engages?

 

[grasscutter]

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.

Are the manifold valves open as you're cracking the hoses at the gauges? Refrigerant canister valve open too?

 

[CDX825]

Are the manifold valves open as you're cracking the hoses at the gauges? Refrigerant canister valve open too?

Valves closed at the manifold. If you are hooking a refrigerant tank to your center hose you should open the tank valve after you have connected the hose and then purge it at the manifold.

 

[grasscutter]

Valves closed at the manifold. If you are hooking a refrigerant tank to your center hose you should open the tank valve after you have connected the hose and then purge it at the manifold.

So that means the manifold valves don't prevent the refrigerant from entering the manifold from the canister, but only prevent the refrigerant from leaving the manifold; correct?

 

[CDX825]

So that means the manifold valves don't prevent the refrigerant from entering the manifold from the canister, but only prevent the refrigerant from leaving the manifold; correct?

Correct when it comes to the standard 2 valve manifold.

 

[hytronbgd011]

Hi,

I totally see your point. I do the same way.
So when I store my gauges I like to keep them free of any refrigerant - Otherwise the pressure in the hoses and gauges will destroy the gauge over time. So my technique is to attach blue and red ports, connect a T at the center input and attach two separate hoses - One I use for the vacuum pump and the other for the refrigerant can. With valves at each connection port closed and refrigerant can closed you want to pull vacuum with a vacuum pump and therefore empty all the air from the hoses. That way you are not introducing any air in the system. Just my way of purging. Also I always fill the hoses with fresh refrigerant so instead of removing refrigerant from the system once you disconnect hoses, I always add a bit (The refrigerant that was in the hoses).
Makes sense?