INTRO (0:00 to 0:30)
ON-SCREEN: black, then two gauge dials side by side, both reading low head and high suction, then text: "Two suspects. One reading."
VOICEOVER: Here is a gauge reading that has cost customers thousands of dollars in wrong repairs. Head pressure low. Suction pressure high. Capacity weak. On a straight-cool system, D26 taught you that picture points at the compressor. On a heat pump, there are two components that produce that exact signature, and one of them costs a fraction of the other to replace. This video gives you the three minute test that tells them apart, plus the defrost diagnostics and the winter baseline that keep you from condemning healthy machines.
MAIN (0:30 to 4:30)
[0:30-1:30] The 2 degree test
ON-SCREEN: D29-two-degree-test.svg, highlight the two suction-side lines, then the probe positions
VOICEOVER: The reversing valve from C19 has four lines, and in any mode two of them are on the suction side: the line returning from the active evaporator coil, and the center line out to the compressor. Inside the valve, those two connect under the slide. The valve is supposed to be nothing but a short tube between those points, and gas does not warm up flowing through a tube. So strap a probe on each line, close to the body, insulated, after ten or fifteen steady minutes of runtime. If the gas leaves the valve less than 2 degrees warmer than it entered, the valve passes. More than about 3 degrees of rise means hot discharge gas is leaking past the slide into the suction stream. That is an internal bypass leak, and NIST measured it as the most expensive fault per percent severity in their whole study.
ON-SCREEN TEXT: Pass: under 2 F rise. Gray zone: 2 to 3 F, retest. Fail: over 3 F. Never within 60 minutes of a defrost.
[1:30-2:20] Valve or compressor: the discrimination
ON-SCREEN: D29-valve-vs-compressor-discrimination.svg, walk down the flow
VOICEOVER: Now the discrimination. Low head, high suction, weak capacity, low amps. A leaking valve and a worn compressor both let compressed gas sneak back to the low side, so the gauges cannot split them. The order is: triangle first, the D24 discipline translated to heating mode, then the valve speaks first, because the 2 degree test takes three minutes. Valve fails, the compressor walks. Valve passes, the compressor is the suspect, and it still gets the full D26 condemnation sequence before anyone orders one. Amps against RLA, the compression ratio capacity check, the functional test. The compressor proves itself. Nobody guesses it dead. And if head and suction have converged hard toward each other with capacity collapsed, that is the stuck mid-shift valve, the slide stalled halfway, the compressor pumping in a circle.
[2:20-3:20] Defrost diagnosis
ON-SCREEN: D29-defrost-diagnosis-flow.svg, follow the chain top to bottom
VOICEOVER: Defrost faults fail in two directions. A defrost that never runs builds ice armor, the coil packed solid in glaze, capacity gone, strips secretly carrying the house. A defrost that runs constantly is a nuisance defrost, air conditioning the house every half hour in winter while the customer watches steam and worries. The diagnostic chain is the same for both. Identify the board, time-temperature or demand. Check the sensor: seated on the right return bend, ohming open at room temperature if it is a defrost stat, matching the resistance chart if it is a thermistor. Force a cycle with the test pins and a sensor jumper, and watch for all four actions from C19: valve shifts, fan stops, compressor keeps running, strips come on. Then watch how it ends. Terminating on temperature, sensor opening between 50 and 80 degrees, means the coil provably got warm. Riding the 10 minute clock every time means it never did, and that is a finding. And pull your jumpers before the panel goes on.
[3:20-4:00] What winter normal looks like
ON-SCREEN: D29-low-ambient-normal-readings.svg
VOICEOVER: Before you condemn anything in winter, load the baseline. Thirty five degrees outdoor, healthy R-410A heat pump: suction around 62 to 78 psig, because the coil boils 15 to 25 degrees below ambient. Head around 317 to 365, because the indoor coil condenses against 70 degree return air. Supply air around 90 to 100 degrees, which feels cool to your 98.6 degree hand and is heating the house just fine. Light frost between defrosts, normal. And capacity falls with the temperature on a perfectly healthy unit: the NIST machine lost about 37 percent of its output between 47 and 17 degrees. Weak heat on the coldest night is, first, physics.
[4:00-4:30] The strips and the power bill
ON-SCREEN: D29-aux-heat-staging-faults.svg, highlight the amp staircase, then the stuck-strip card
VOICEOVER: Last suspect: the strips. Verify staging with a clamp meter, each 5 kW bank stepping in as roughly 21 amps. And on every winter high-bill complaint, ask one question: who is making the heat, the compressor or the strips? A welded sequencer leaves a bank running with no call. A thermostat configured as a furnace runs strips as primary heat with the compressor idle. One clamp reading at the air handler with the stat satisfied screens all of it.
OUTRO (4:30 to 4:45)
ON-SCREEN: the five SVGs as a grid, then title card: "D29 v2: Darrel stages the fault. You catch it."
VOICEOVER: Two probes, a clamp meter, and a baseline. That is heat pump diagnosis. In the demo, Darrel stages a real fault, runs the 2 degree test on camera, forces a defrost, and makes the valve versus compressor call with numbers on the ticket. Read the article, then meet him at the unit.