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How To Read Ac Gauge

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  • Location: Riverside, CA
Here's what's happening when I connect an AC gauge to the low side port:

1) Compressor off, reads ~40psi

2) Compressor kicks on, gauge quickly (<1sec) drops to ~10psi, causing the compressor to turn off again.

3) Compressor off, gauge now slowly (~5 sec) goes back up to ~40psi

4) Repeat step 1.

What does this mean?

I don't think I need to add freon, nor is there a leak.

What else could be the problem?




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  • Location: Texas
  • Car: 1998 Mazda 626, 2.0, Auto
If the compressor kicks on and pressure drops to 10 psi it sounds to me like you to need to add freon.

I believe you are supposed to read the A/C gauge when the compressor kicks on.

As you add more freon the compressor should stay on longer.

Hopefully you have a A/C gauge that tells you the proper psi to charge the system.

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I agree that you're just low on refrigerant. With the A/C compressor kicked on you should read around 35psi. Goes way up when the compressor is off.

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