Mechanical Business Jan/Feb 2018

Page 30

HVAC TOP TIPS B y Ma r k Pa r l i a m e n t a n d A l e x a n d r a W en n b er g


maintenance checks



ost parts of the country have experienced one of the colder winters in recent memory, and the cold keeps HVACR technicians busy as furnaces falter and the calls for winter maintenance just don’t seem to ever stop. Frustration can mount when a furnace is not working properly and the indoor temperature continues to fall, despite following the maintenance check-list. Sometimes the issues are due to additional failing parts, but other times it’s the procedural steps that block the path to a fix. In the spirit sharing knowledge, and to help get you to your next no-heat call quickly, here are three common component errors made in the field that could cause a furnace to fire improperly, or worse, not at all. And remember, no matter how long one has been working in the

field, one can never learn too much or know too much. You can be the type of technician that is hesitant to jump at emerging technologies or the one who embraces the new and looks for the latest products to work into the systems you are installing. Regardless of your stripes,

only you are in charge of your knowledge level, so strive to learn something new every day by trying different ways of troubleshooting appliances, reading manufacturer manuals, registering for industry courses or signing up for online industry blogs and forums and keep reading magazines like this one.

MANIFOLD PRESSURES AND SEALED COMBUSTION With a direct vent furnace equipped with a sealed combustion burner, it is important to check the manifold pressure to ensure that the system is not over-fired. Over-firing can lead to premature limit failure, damage to the heat exchanger, improper combustion and CO poisoning. At one time, we would check the manifold pressure with the burner box cover removed or by disconnecting the hose from the gas valve and plugging it, leaving the valve vent open to the atmosphere. These burners run in slightly negative pressure, however. By removing the cover or disconnecting the hose, the manometer does not see the negative pressure and could easily over- or under-fire the unit while in operation. Instead, it is recommended to insert a tee in the hose from the gas valve vent to the burner box. The other end of the tee is then connected to the negative port on the dual port manometer. This way you can see the operating pressure of the unit while running in true load conditions.


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