In my column that ran in the February issue I suggested it would be better for HVAC service techs to use thermometers rather than manifold gauges when doing preventive maintenance calls.
As I explained, connecting the manifold creates all sorts of contamination problems. It too often results in refrigerant leaks that require a callback. And on the new high-pressure systems, a lot of refrigerant often is lost when connecting and disconnecting the hoses.