Rooftop Units (RTUs) error codes, explained
Packaged rooftop units, all brands, ~3–25 ton — the machine over most offices. Codes below: Common failure guides (economizers, belts, drains). Each guide covers what the code means, what you can safely try yourself, when to stop and call a technician, and what the repair typically costs.
Rooftop unit economizer not working (most offices have this and don't know)
Here's a statistic worth knowing if your office sits under a rooftop unit: field studies have repeatedly found that 60–80% of RTU economizers — the dampers that should be cooling your office with free outside air — are not working properly (64% in NBI/PIER field research, 80% in PG&E's study of existing units, ~two-thirds across studies compiled by ACEEE and New Buildings Institute). A failed economizer doesn't break your AC; it silently runs the compressor when outside air would do the job, wasting $1,000–$3,700 per unit per year by DOE-cited estimates.
Rooftop unit basics for office managers — belts, filters, drains
The unglamorous truth about the machine on your roof: the failures that actually take offices down are cheap parts nobody checked. A worn $30–$60 blower belt that snaps means no airflow — and can cascade into a $3,000–$8,000 compressor failure. Clogged filters and dirty coils show up in field studies as inadequate airflow in 40–70% of units. Clogged condensate drains announce themselves as ceiling stains and roof leaks. Quarterly PM on these three items prevents the large majority of emergency calls.