#heat exchanger

Tech Tips:

There are two camps I've run into regarding cracked heat exchanger diagnosis. There are those who look for it everywhere and those who dismiss it and never look. I will start by saying that everything I write here is my own opinion and experience. Because this is such a hot-button topic, don't take my word […]

Heat Exchangers and Temperature Rise – Short #227

In this short podcast episode, Bryan talks about heat exchangers and temperature rise in gas furnaces, especially 80% open-combustion gas furnaces. Temperature rise is the difference between the return air temperature and supply air temperature; in cooling, we usually refer to this difference as a delta T or temperature split. The manufacturer sets a […]

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In this short Q&A podcast episode, Bryan answers a listener-submitted question about circuit board troubleshooting: is there a quick way to learn how to check circuit boards, and if so, where are those resources?

A circuit board is a bunch of components put together on a printed circuit board (PCB). There isn’t a lot of helpful universal information about circuit boards available, as they vary quite a bit by model and manufacturer. However, many of the basic components will be the same across circuit boards: microprocessors, diodes, relays, capacitors, and transformers. If you understand what these are on their own, that will help you understand what they do in circuit boards.

You mostly need to know the inputs, outputs, and sequence of operation of a circuit board to diagnose it. The sequence of operation tells you when certain things are supposed to happen, such as in an integrated furnace control (IFC); the flame rectification process is a classic example. If the flame can be proven, the operation continues; if it can’t be proven, then that will cause a lockout (possibly due to improper grounding or poor placement and NOT necessarily because of the board).

A lot of issues with the board can be diagnosed if you understand the inputs and outputs (e.g., 24v signals) or observe it with your senses, such as bloated capacitors or ant nests. Becoming a master of the obvious and checking the manufacturer’s literature are the top two things you can do to diagnose circuit boards.

HVAC Control Systems by Ronnie Auvil

Electricity for Refrigeration, Heating, and Air Conditioning by Russell Smith

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