Chapter 19 Key Takeaways: Air Conditioning and Cooling Systems
The Core Concept
Your AC system moves heat — from inside your house to outside. It does not create cold. The refrigerant cycle picks up heat at the indoor evaporator coil (absorbing it from your house air), carries it to the outdoor condenser unit, and dumps it outside. Understanding this makes every other AC concept easier to grasp.
Air conditioning also dehumidifies — moisture condenses on the cold indoor coil and drains away. Dehumidification is as important to comfort as temperature.
The Refrigeration Cycle
Four components; four steps: 1. Evaporator coil (inside): Cold, low-pressure refrigerant absorbs heat from house air and evaporates 2. Compressor (outdoor unit): Squeezes refrigerant vapor, raising pressure and temperature 3. Condenser coil (outdoor unit): Hot refrigerant releases heat to outdoor air and condenses to liquid 4. Expansion valve: Drops refrigerant pressure, cooling it for return to the evaporator
SEER Ratings and Operating Cost
- SEER = cooling BTUs out ÷ electrical watt-hours in (over a full season)
- Since January 2023, SEER2 is the standard — slightly lower numbers for the same equipment
- Calculate your savings: Every increase of 1 SEER reduces operating cost by about 7%
- The biggest gains come from replacing very old equipment (SEER 8–10 is common pre-1992)
- Marginal gains from SEER 18 vs. SEER 14 may take 10+ years to pay back — run the numbers for your situation
- System sizing affects efficiency as much as SEER: oversized systems short-cycle, killing humidity control
Refrigerant Transitions — What You Need to Know
| Situation | Implication |
|---|---|
| R-22 system (pre-2010) | Recycled R-22 available but expensive ($50–150/lb). Repair vs. replace decision critical when leak develops. |
| R-410A system (2010–2024) | Can be recharged normally; not yet being phased out of use. New R-454B/R-32 equipment available but not required until replacement. |
| Buying new equipment (2025+) | Expect R-454B or R-32 — lower environmental impact, mildly flammable but safe under normal conditions. |
R-22 systems cannot be converted to R-410A or R-454B — the systems operate at different pressures and the equipment is incompatible.
Common Failures and Responses
| Symptom | Most Likely Cause | Your Action |
|---|---|---|
| Reduced cooling | Dirty filter | Replace filter immediately |
| Reduced cooling | Dirty condenser coil | Rinse outdoor unit (power off first) |
| Ice on coil | Dirty filter or low refrigerant | Shut off, thaw, then diagnose |
| System won't start | Tripped breaker, failed capacitor | Check breaker; call tech for capacitor |
| Warm air from registers with system running | Multiple possible causes | Full diagnostic sequence; probably professional |
| Water dripping near air handler | Clogged condensate drain | Clear drain; treat with bleach solution |
🔴 Never run a system with an iced coil — risk of liquid refrigerant reaching the compressor and destroying it.
Mini-Splits
- Same refrigerant cycle as central AC, just distributed to room-level air handlers without ductwork
- Best applications: additions, rooms without duct service, homes without existing ductwork, new construction
- Individual zone control per indoor unit is a genuine comfort advantage
- Cold-climate models (Mitsubishi, Daikin, Bosch, Fujitsu) maintain capacity to -13°F
- Filtration is simple mesh only — not a substitute for central system media filtration
- Refrigerant work requires EPA 608 certification — not a pure DIY project
Annual Maintenance Rhythm
Spring startup: New filter, clear outdoor unit, check and clean condensate drain, inspect refrigerant line insulation, test run.
Professional annual service: Check refrigerant charge, clean coils, measure capacitor and motor amperage, verify condensate drain, inspect electrical connections.
Fall shutdown: Clean outdoor unit, note any performance issues for spring service, consider a breathable cover in climates with severe ice.
The Oversizing Problem
The most common AC installation mistake is oversizing — installing more capacity than the house requires. Oversized equipment: - Short-cycles (frequent on/off cycling) instead of running long cycles - Fails to dehumidify because run cycles are too short for moisture removal - Wears out faster from the repeated starts - Costs the same or more than a correctly-sized system
Insist on a Manual J load calculation before any new system installation. Reject contractors who size by rule-of-thumb alone.