FA-92438 / HVAC thermostat control / Member archive

Defrost timer accumulates runtime with a dry coil · case 03

The unit defrosts on schedule in dry mild weather even though the coil never got cold enough to frost.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Heat pump time-temperature defrost sampled per minute (degrees F); samples are [compressor_running, coil_temp, outdoor_temp]. Compressor run minutes accumulate only while coil <= 32. When the accumulation reaches interval and outdoor <= 50, defrost starts that minute and the accumulation resets; otherwise the accumulation keeps growing. Defrost ends on the first later minute with coil >= 57 or when it has lasted max_minutes minutes; that minute reports normal operation. Return heat, off or defrost per minute.

Why this case matters

Residential and light-commercial thermostats make these decisions sample by sample; each defect changes equipment calls in a way that shows up as short cycling, comfort complaints or equipment stress.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: scenario 2	`["heat", "heat", "heat", "defrost", "defrost", "defrost", "heat", "heat", "heat", "heat", "off", "defrost", "defrost", "defrost", "heat", "heat", "heat", "heat", "heat"]`	`["heat", "heat", "heat", "heat", "off", "heat", "heat", "heat", "heat", "heat", "off", "heat", "off", "off", "heat", "heat", "heat", "heat", "heat"]`	Failed

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