Anatomy & pictorials

A career plumber knows what a boiler room looks like before they read about one. A career tech reads a schematic and sees the cabinet in their head. For someone crossing trades, the missing piece is the second habit — the mental picture that turns a symbol into a part you can touch. These pictorials exist to build that habit.

System-level view — the big picture first

Before any component-level diagnosis, the reader needs to mentally place everything: the stat on the wall, the air handler in the basement closet, the condenser in the yard, the thermostat wire that connects them, the line-voltage feed that powers them. This is the picture every chapter implicitly assumes you already have.

Gas furnace — what's inside the cabinet

The single most-referenced piece of residential equipment. Everything in Part 5 — ignition modules, gas valves, flame sensors, limits, pressure switches, blower motors — lives inside this cabinet. Memorize where each component sits and half the chapters turn from abstract into concrete.

AC condenser — what's inside the outdoor unit

Opening an outdoor unit for the first time is disorienting. The layout looks different from the furnace: compressor and fan motor dominate the volume, the control components are crammed into a small access compartment, and almost everything is 240 V hot the instant the disconnect is in.

Boiler room — job-site view

Boiler rooms read chaotic until you've seen a few. The electrical story is surprisingly simple — one service switch, one aquastat, zone controls, one or more circulators — but the piping hides the wire runs, so the pictorial has to show both. This diagram traces the thermostat call from wall to pump through the physical layout every tech sees on arrival.

Probe-placement pictorial — µA flame signal

The most commonly-run test on a gas furnace, and the one where probe geometry matters most. Getting this pictorial into the reader's head prevents the classic mistake of trying to read flame signal as an AC voltage across R and C. The meter goes in series with the sensor's wire — not across it.

Photo annotations — for your own job-site images

The drawn pictorials above explain how systems work in the abstract. But there's no substitute for a real photograph of a real piece of equipment when you want to say "this is what a Copeland scroll compressor actually looks like sitting on a pad in a Jersey driveway." The <PhotoAnnotation> component takes any image and overlays numbered technical callouts — same visual language as the pictorials, but with your photos underneath. Drop in a photo from your phone, a licensed stock image, or a Wikimedia Commons shot, specify where the callouts anchor in percent coordinates, and the component handles the rest.

Demo — replace the placeholder with a real photo

1. 1

   Inducer motor

   establishes draft before ignition

2. 3

   Burner tubes

   manifold + 4-tube array

1 2 3 4

1. 2

   Pressure switch

   proves inducer draft to IFC

2. 4

   Blower assembly

   PSC or ECM · scroll + wheel

1. 1
   Inducer motor — establishes draft before ignition
2. 2
   Pressure switch — proves inducer draft to IFC
3. 3
   Burner tubes — manifold + 4-tube array
4. 4
   Blower assembly — PSC or ECM · scroll + wheel

import PhotoAnnotation from "@/components/illustrations/PhotoAnnotation.astro";

<PhotoAnnotation
  src="/photos/condenser-interior.jpg"
  alt="Carrier condenser with access panel removed"
  title="Service call — 8/14/2026"
  annotations={[
    { x: 72, y: 38, num: 1, label: "Run capacitor",
      detail: "swollen top · failed", side: "right" },
    { x: 45, y: 52, num: 2, label: "Contactor",
      detail: "burn marks on L2 lug", side: "right" },
    { x: 40, y: 78, num: 3, label: "Compressor terminals",
      detail: "C/S/R under cover", side: "left" },
  ]}
/>