INTRO
0:00-0:30
[SHOT] Darrel at the open furnace, meter in hand, manometer hanging on the cabinet.
DARREL: This furnace has three faults in it, and I planted all three. You will not see me guess once. I am going to run the sequence you learned in C18, let the furnace stall, name the fault family from where it stalled, and then prove each fault with a number before I touch a single part. That is the whole method. Watch.
MAIN
[0:30-1:30] One cycle, eyes only
[SHOT] Wide on the cabinet: burner compartment, inducer, and board all in frame. Darrel initiates the call for heat and steps back, narrating with hands off.
DARREL: Call for heat is in. Hands in pockets, eyes open. Inducer is running... there is the pressure switch click... igniter should be glowing about now. Look in the burner box: nothing. No glow. The sequence climbed three rungs and died on rung four. So I am not chasing the gas valve, not the flame sensor, not the blower. The stall point says ignition hardware, and that is the only family I am allowed to work in right now.
[ON-SCREEN] Text overlay: STALL = IGNITER NEVER GLOWS. FAULT FAMILY: IGNITION.
[1:30-3:30] Fault one: the igniter, eyes, ohms, volts
[SHOT] Close-up. Power off. Darrel removes the igniter, holds it to the light by the body, never touching the element.
DARREL: Test one is eyes. Hold it to the light... and there it is, a hairline crack across the element. A cracked igniter can still read fine cold, because the crack closes up at room temperature and opens when it heats. Test two anyway, because I want the habit on camera: meter on ohms, across the plug.
[SHOT] Insert: meter display reading OL, or a number far out of range.
DARREL: This one reads open, so it is dead twice over. A healthy silicon carbide element reads somewhere around forty to ninety ohms cold, and the spec sheet for the exact part is the real referee. Now the third test matters when the igniter checks good but never glows: volts under command. Meter on AC volts at the plug, run the sequence, and if one twenty shows up in the warm-up window with no glow, the igniter is condemned. If no voltage shows up, the igniter is innocent and the board output or harness is your fault. Inputs and outputs, same D23 logic as always.
[SHOT] Darrel installs the replacement igniter, handling by the body.
DARREL: New element goes in by the body only. Fingers never touch ceramic, skin oil cracks them. That is fault one found, proven, and fixed.
[3:30-5:30] Fault two: lights, then drops
[SHOT] Wide. Darrel runs the call again. Burners light, hold a few seconds, drop out. Let the retry happen on camera.
DARREL: New stall. It glows, it lights, and... gone. Three, four seconds of fire and the valve slammed shut, and it will retry and do it again. Lights-then-drops is the signature of exactly one family: flame sensing. The fire was real, the proof of fire failed. So my meter goes in series with the sensor, DC microamps.
[SHOT] Close-up: Darrel kills the call, disconnects the sensor lead, clips the meter between lead and rod terminal, runs the furnace again. Insert on the meter display during the brief burn.
DARREL: Watch the number during the burn... zero point six microamps. Healthy is one to six, and most boards drop the valve somewhere under about one. There is my proof. Now the discipline: I do not condemn this sensor yet. I clean it and I retest it.
[SHOT] Close-up: rod removed, polished with a fine abrasive pad, wiped, reinstalled. Meter back in series. Furnace runs and holds.
DARREL: Fine abrasive only, never a coarse file, a scarred rod just grows oxide back faster. Reassemble, rerun... four point three microamps, and the burners are holding. Dirty number, clean number, both go in the ticket. That is a thirty second repair that a parts changer turns into a sensor sale, and if cleaning had NOT fixed it, the same measurement sends me to the ground path, the porcelain, line polarity, and gas pressure, in that order.
[ON-SCREEN] Text overlay: 0.6 uA DIRTY, 4.3 uA CLEAN. RECORD BOTH.
[5:30-8:00] Fault three: the inducer that runs forever
[SHOT] Wide. Darrel runs the call again. Inducer spins up and runs continuously. Nothing else happens. Hold the shot long enough to feel the stall.
DARREL: Listen. Inducer running, running, running, and no click, no glow, no gas. The board is waiting on the pressure switch and the switch will not close. Here is the most important sentence in this video: an open pressure switch almost never means a bad pressure switch. It is a report about draft. So I do not grab a switch off the truck, I grab the manometer and I tee into the hose.
[SHOT] Close-up: Darrel kills power, tees the manometer into the pressure switch hose, points at the rating printed on the switch body.
DARREL: Printed right on the switch: this one makes at minus zero point six inches of water column. The question is whether the inducer is delivering that draft. Power back on, call for heat, read the meter.
[SHOT] Insert: manometer reading near zero, far short of the rating.
DARREL: Almost nothing. The switch is innocent, it is refusing to close because there is genuinely no draft to prove. So the fault is upstream: inducer, hose, vent, or condensate. Flashlight time.
[SHOT] Darrel traces the hose from the switch toward the inducer and finds it pulled off the inducer tap. He holds it up to camera before reconnecting.
DARREL: And there it is, the hose is off the tap at the inducer. Reconnect, rerun.
[SHOT] Insert: manometer now reading past the rating; the switch clicks, the sequence proceeds to full fire.
DARREL: Minus one point one against a minus point six switch, click, and the whole sequence climbs. On a real call this same stall is a weak inducer, a blocked flue, a bird nest on the roof, or on a ninety percent furnace a plugged condensate trap backing water into this very hose. The manometer against the printed rating sorts the innocent switch from the guilty one, every time, in two minutes.
[ON-SCREEN] Text overlay: MEASURED DRAFT vs PRINTED RATING. THE SWITCH IS THE MESSENGER.
[8:00-9:30] Verify like it matters: full cycle and combustion check
[SHOT] Wide. The furnace runs a complete uninterrupted cycle. Darrel connects the manometer to the gas valve outlet tap, then sets up the combustion analyzer probe in the flue.
DARREL: Three faults found, three proven, three fixed. Now the furnace has to earn its sign-off. Full cycle, no interruptions: call, inducer, prove, glow, gas, flame, blower, all in order. Manifold pressure with the burners firing: three point five inches of water column, natural gas, on the nose. And because we were inside the ignition and draft systems today, the analyzer comes out.
[SHOT] Insert: analyzer display. Darrel reads the numbers aloud.
DARREL: Oxygen seven and a half percent, right in the six to nine window for an eighty percent furnace. CO air-free, twenty two ppm, comfortably under a hundred. Stack temperature in range for the category. And one more habit while it fires: watch the flames the moment the blower starts... no waver, no lift, no change. A flame that dances at blower start is house air getting into the fire side of that heat exchanger, and that is a conversation backed by evidence, never by vibes.
[SHOT] Close-up: gas off, manometer adapter out, tap plug back in, bubble solution on the plug.
DARREL: Tap plug back in and bubble tested, same as C18, because a loose tap is a leak you built.
[9:30-10:30] The line you never cross
[SHOT] Darrel closes the burner door, faces camera, deliberately slower.
DARREL: Last thing, and I want it said at the furnace, not in a classroom. Every stall you saw today was a safety doing its job. The pressure switch refused to allow gas without draft. The flame sense refused to allow gas without fire. There will be a night, some January, customer with kids, parts house closed, where a jumper wire would make heat right now. You do not do it. Not for ten minutes, not while you wait for a part, not ever. A bypassed safety is how a no-heat call becomes a carbon monoxide call, and no cold night is worth that trade.
OUTRO
10:30-11:00
[SHOT] Darrel at the closed, running furnace.
DARREL: One cycle watched. Stall named. Number proven. Repair made. Verified with a full cycle and the analyzer. That ladder is your practical for this module: I will plant the faults, you will find them exactly the way I just did. The furnace tells you where it hurts. Come show me you can listen.