HVAC in the District of Columbia has to pull humidity out of brick rows that hold heat, and it still has to heat those houses when a winter night drops. Top floors bake. English basements stay clammy. Detached houses under trees have a different load, shady and damp rather than blasted by the street. Radiators remain in many older homes. Ducts, where they exist, are squeezed into chases that were never drawn for them.
Outdoor units live in alleys and side yards with poor clearance, lint, and heat bouncing off brick. A condenser that cannot breathe will ice or quit in August weather that is already hard. Inside, a boiler in a basement can be old, loud, and uneven, leaving the top floor cold. If you have radiators and a window unit, say so. Do not describe a patchwork as a single central system.
Name the floor that fails. The top will not cool. The garden bedroom smells when the heat starts. The basement short-cycles. A thermostat in a drafty hall lies about a room under a flat roof. Brick gives the afternoon back at night, so the house stays hot after the sun drops. That is a District habit. A wooded house may have the opposite problem: little sun and a lot of damp.
Say the fuel if you know it, and where the equipment sits. A checkup before the humid months and a no-heat morning are different calls. Do not guess the failed part. Filters, blocked returns, and a crushed duct can mimic a dead machine. Party walls pass noise. They do not reliably pass heat to a neighbor and they will not cool your top floor.
HVAC in the District of Columbia is top-floor heat, basement damp, alley equipment, and old radiators inside long brick rooms, plus the occasional detached house in the trees. Call the number on this page.