HVAC Gauges, Analog vs. Digital vs. Probes

HVAC Gauges, Analog vs. Digital vs. Probes

Bryan with HVAC School goes over some of the common differences between analog gauges, digital manifolds (with the Testo 550), and probes. We examine the benefits of each and discuss their ideal uses.
By Bryan Orr

Many people learn on an analog manifold, as you have to be able to calculate superheat and subcooling on your own with a line temperature clamp. So, the analog manifold is a good teaching tool; by comparison, the digital manifold gives you the answers and doesn’t make you familiarize yourself with the math required in HVAC work. The analog gauges also show saturation temperatures for a few different refrigerant types.

However, analog gauges have low resolution, and it can be difficult to get exact measurements in the field. On microchannel condensers and critical-charge systems, those mild inaccuracies can actually be pretty significant. Line temperature clamps must also be calibrated separately and may use K-type thermocouples, which tend to be less accurate than the thermistors used with clamps for digital manifolds.

It’s much easier to zero out digital manifolds, as you press a button with your hoses open instead of removing lenses and adjusting needles manually. Digital manifolds can tell you your evaporator temperature (EV) and condenser temperature (CO) all on one display. You can also select the refrigerant type (reducing the probability that you’re looking at the wrong refrigerant scale) or go into superheat/subcooling mode. Digital manifolds also tend to be a bit more accurate, as do the line temperature clamps that connect to them.

You can also use wireless probes for non-invasive testing. They have a similar level of performance as digital manifolds, but they’re smaller and reduce the risk of refrigerant losses through hoses. However, you have to add a tee for charging and recovery, as you can’t pull through the probes themselves.

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