How do you read a/c manifold gauges?

[Robert Coats]

Starting to learn about the a/c system on my 964 (1991) and bought manifold set. However, the instructions are less than clear. I figured out how to connect it to the car, but not sure if I'm reading/using the manifold correctly. Here's what I did, and please tell me if this is right/wrong or what... Closed red and blue handwheel valves on manifold. Opened red and blue knob valves at the end of each read and blue hose. Connected loose end of the yellow hose onto its nipple on the manifold. Connected red and blue hoses to fittings on a/c system (nice they are different sizes and you can't screw it up). Started engine, engaged a/c compressor button. Compressor running fine. Opened red and blue handwheel valves on manifold 1.5 turns each (per instructions). Both read and blue gauges stablized at almost exactly 140 psi each?!? Something ain't right...I'm too low on the high side, and too high on the low side from what I've read, OR, I'm not doing something right. So, if I did use the tool correctly, what is the likely problem? If I did not use the tool correctly, please tell me how. All help/suggestions are welcome.

[GB83SC]

I found this on the web the other day, see if this helps.


Red to high side, blue to low side... That is pressure, not hieght..If your system is empty, a vacuum needs to be pulled. If there is positive pressure, you can top it off. Hook the "BLUE" line to the low side fitting, and the "RED" line to the high side fitting, The yellow is for the refrigerant. make sure you purge the air out of the lines before adding. Add refrigerant until the high side is about 2.2 times the outside temp. Check the cooling. Best to charge when the outside temp is above 70 degrees. Make sure the "wheel" on the high side (RED) is closed while checking pressures and charging.. Otherwise the pressure can blow up the can...Be careful!!!

[turbo6bar]

Robert, unless you are using some funky gauges, you do not need to open the valves. What you are doing is connecting the high and low sides of the system. When you do that, the pressure is going to be equal for the entire system.

Read the gauges with the valves closed. You only open a valve when you're extracting or adding refrigerant. 9 times out of 10, you will be operating the blue valve, or the low side. You can open the high side when you're pulling a vacuum, or when you're charging an empty system with liquid or gas refrigerant.

Hope this helps.

Jürgen

[walt]

Jurgen is correct, the manifold is designed to read pressure with the valves closed. You only open the valves to connect the center hose to either side.

[Robert Coats]

Originally posted by turbo6bar
Read the gauges with the valves closed. You only open a valve when you're extracting or adding refrigerant.

Picture time...just be sure:



To read pressures on the system, I open the valves (1) and (2) and connect them to the high and low side fittings, make sure (3) and (4) are closed, then start the engine and a/c and read direct.

Is this right?

[turbo6bar]

That's right!!!

Jürgen