You do not need gauges to learn whether the machine is moving heat. You need time and a $10 thermometer.
How
- System calling for Cool (or Heat) for at least ten minutes.
- Return = the large grille that sucks air back. Hold the probe in the airstream, not against the paint.
- Supply = a vent that is blowing in a room you use. Same idea.
- Subtract.
Cooling in this climate often shows about 14–22°F of drop (return minus supply). Heat pumps in heat are a different, wider band. Under about 8°F while the outdoor unit is clearly running means it is not doing the job.
Fan On with no call for Cool will look like a 0–2° “split.” That is room air in a circle. Set fan to Auto and test again.
What a bad split is not
It is not a coupon. It does not tell you the exact leak location. It tells you the visit is real. Combined with ice and a dirty filter, it is almost always airflow. Combined with a clean filter and a spinning outdoor fan, it is a licensed diagnosis.
Enter the two numbers in the Toolbox if you want them in the notes when you book. Or skip. We will measure on site either way.