What do manifold gauges measure?

Manifold gauges are essential tools used primarily in refrigeration and air conditioning systems, where they measure the pressure in the system. Specifically, they gauge pressure compared to atmospheric pressure, which is crucial for diagnosing and servicing HVAC systems. By providing a clear indication of both high side and low side pressures, manifold gauges allow technicians to assess the system's performance accurately.

When pressure readings are taken, they can determine if the system is charged correctly, identify issues like leaks or blockages, and evaluate the overall health of the refrigeration cycle. Understanding the pressure in relation to atmospheric conditions is vital because it facilitates comparison between the operating pressures and the expected normal pressures for that system, allowing for effective troubleshooting.

Other options such as temperature differences or focusing solely on high or low pressure do not encompass the full functionality of manifold gauges, which are designed specifically to measure pressure against atmospheric levels in both high and low settings. This capability makes option B the correct choice.