Arkansas HVACR NewsMagazine January 2024

HVACR NewsMagazine January 2024

Tech News

furnace plug. Corrosion and cracks on the grounded components will indicate that there is a problem.

Tools and Parts for 90%+

The most important tool you could keep on hand when troubleshooting a 90%+ furnace isn’t an HVAC tool at all. It’s your phone. Your smartphone allows you to look up service manuals, many of which have diagnostic flow charts. And if the service manual doesn ’t help, you can always call tech support. Apart from having a means of looking up information, your most important tool for troubleshooting 90%+ gas furnaces will be a manometer to measure pressure and test pressure switches. Another important tool would be a good digital thermometer to measure temperature rise across the furnace. It’s also a good idea to have a way to measure airflow, such as with a TrueFlow grid. You can also calculate airflow with temperature rise and blower charts. An underrated tool is the humble level. If you have a level on hand, you can rule out problems with the drain pitch and ensure that the unit and drainage assembly were installed according to the manufacturer’s specs (and local codes). While 90%+ high-efficiency furnaces are quite different from 80% furnaces and can be intimidating at first glance, you’ll get the hang of them as you spend more time looking at them and reading manuals. You’ll eventually grasp the unique needs of these systems and the most common things that could go wrong, several of which we’ve covered here and in the livestream, which you can watch in its entirety HERE.

Flame rods tend to foul more quickly on LP units than natural gas ones, and they’re also more likely to get dirty if a furnace’s air intake is in an area with lots of VOCs, such as those given off by household cleaners. Keep in mind that you’ll want to check the burners, too. Dirty or rusted burners can affect flame rectification, and they can even lead to higher CO levels. Correctly grounding a 90%+ furnace is necessary for flame rectification. During flame rectification, an electrical current flows through the flame and to the rod to close the switch. (The electrical potential in the flame sensing terminal and the ions in the flame allow an electrical path to form between the rod, through the flame, and to ground.) Reversed polarity or improper grounding won’t allow a completed DC microamp flame signal to travel to the board and prove the flame. The system needs to be grounded from the burner to the cabinet, the board, and the Grounding