FA-92545 / HVAC thermostat control / Member archive

Mixed-air low limit reads the outdoor air sensor · case 05

The damper throttles back on cold mornings even when the mixed air is warm enough, and fails to protect when it is not.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Rooftop economizer per sample; samples are [outdoor, return_air, cooling_call, mixed_air, occupied] in tenths F. Economizing is enabled when outdoor <= high_limit - 2.0 F and outdoor < return - diff, and disabled when outdoor > high_limit or outdoor >= return. Unoccupied: damper 0%. Occupied, enabled and cooling: if mixed air < mat_low the damper steps down 10% but not below min_pos, otherwise it steps up 20% from at least min_pos, capped at 100%. Otherwise the damper sits at min_pos. Return [enabled, damper%] per sample.

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 6	`[[true, 30], [true, 0], [true, 30], [true, 30], [true, 30], [true, 0], [true, 0], [true, 0], [true, 30]]`	`[[true, 50], [true, 0], [true, 50], [true, 40], [true, 30], [true, 0], [true, 0], [true, 0], [true, 30]]`	Failed

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