I have been using my low side gauge to pull a vacuum, is this wrong?

I have been using my low side gauge to pull a vacuum, is this wrong?

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I have been using my low side gauge to pull a vacuum, is this wrong?

Yes, it is generally incorrect to only use a low-side gauge to pull a vacuum on an HVAC or refrigeration system. While a low-side gauge can indicate a vacuum, it doesn’t accurately measure the depth of the vacuum or the presence of non-condensable gases and moisture. For proper evacuation, a micron gauge (which measures vacuum in microns) is essential and should be used on both the high and low sides of the system. 

Here’s why using only a low-side gauge is insufficient:
  • Inaccurate Measurement:
    A low-side gauge only measures pressure relative to atmospheric pressure and doesn’t provide the fine-grained measurements needed to ensure a proper vacuum. 

  • Inability to Detect Moisture and Non-Condensables:
    A low-side gauge cannot detect moisture or non-condensable gases, which can negatively impact system performance. 

  • Potential for Trapped Moisture:
    Pulling a vacuum only on the low side can trap moisture and other contaminants in the high side, leading to system inefficiency or damage. 

  • Need for Micron Gauge:
    A micron gauge is necessary to accurately measure the vacuum depth and ensure it’s deep enough to remove all moisture and non-condensable gases. 

Proper Evacuation Procedure:
  1. ۱٫ Connect a manifold gauge set:
    Connect the manifold gauge set to both the high and low-side service ports of the system. 

  2. ۲٫ Use a micron gauge:
    Connect the micron gauge to the system, preferably on the high side or as close to the system as possible, to accurately measure the vacuum. 

  3. ۳٫ Pull vacuum simultaneously:
    Use a vacuum pump to pull a vacuum on both the high and low sides of the system at the same time. 

  4. ۴٫ Maintain vacuum:
    Keep the system under vacuum for at least 15-30 minutes, monitoring the micron gauge to ensure the desired vacuum level is reached and maintained. 

  5. ۵٫ Isolate and test:
    Once the desired vacuum level is reached, isolate the system and observe the vacuum reading on the micron gauge to check for leaks. 

YES. The low side gauge knows only atmospheric pressure and cannot sense moisture or non-condensables. A micron gauge is a heat sensing device that not only reads atmospheric pressure, but also measures the gases created by the vacuum pump as it boils the moisture. For example, if you were to pull a vacuum on an enclosed bottle of water, the low side gauge when pulling a vacuum will read a perfect vacuum. Using a micron gauge, it will immediately tell you with a high reading the you have a problem in you system.