🔧 HVAC Troubleshooting & Maintenance Encyclopedia

🥵

AC Running But Not Cooling: Diagnosis Dirty condenser coils, frozen evaporator, refrigerant leak, or failed compressor—how to triage each cause before calling a technician.

🔄

AC Short Cycling: Causes & Fixes Oversized unit, clogged air filter, refrigerant low, or thermostat location error—short cycling destroys compressors. Diagnose the root cause before the compressor fails.

💨

Refrigerant Leak: Signs & EPA Regulations Hissing sounds, ice on coils, and declining cooling—R-410A phaseout and why topping off without fixing the leak is illegal and expensive waste.

🧊

Frozen Evaporator Coil: Why It Happens Low refrigerant or low airflow (dirty filter, blocked returns)—ice on indoor unit means turn it OFF immediately. Running a frozen system floods the compressor with liquid refrigerant.

⚡

AC Capacitor Failure: Symptoms & Replacement Humming but fan not spinning, or compressor won't start—the most common AC failure. Start vs run capacitors and why a $20 part causes a $300 service call.

🔧

Compressor Failure: Repair vs Replace Decision Compressor replacement costs $1,500-$2,800—on a 10+ year old system, replacement is usually smarter. The $5,000 rule: repair cost × age > $5,000 = replace.

🔊

AC Strange Noises: Diagnosis Guide Squealing (belt/blower motor), grinding (compressor bearings), buzzing (electrical/contactor), rattling (loose panel or debris). Sound ID before the tech arrives.

🏠

Central AC vs Ductless Mini-Split Ductless efficiency (no duct losses = 30% energy saved), multi-zone capability, and installation cost comparison. Why mini-splits dominate in homes without existing ductwork.

🥶

Furnace Not Producing Heat: Troubleshooting Check thermostat batteries, filter, and gas valve before calling. Pilot light vs electronic ignition—different no-heat scenarios for each system type.

🌡️

Furnace Short Cycling: Overheating Shutdown Dirty filter, blocked vents, or failing limit switch causing safety shutdown. Why repeated short cycling cracks the heat exchanger—a carbon monoxide risk.

☠️

Cracked Heat Exchanger: CO Danger The most dangerous furnace failure—carbon monoxide leaks through cracks. Flame disturbance pattern test and why a cracked heat exchanger means furnace replacement, not repair.

🔥

Pilot Light Won't Stay Lit Thermocouple failure, gas valve issue, or draft blowing out the flame. Troubleshooting older standing-pilot furnaces vs modern hot surface igniter systems.

⚖️

Gas Furnace vs Heat Pump: Cost Comparison Operating cost by climate zone, carbon impact, and dual-fuel systems that switch based on outdoor temperature. The IRA heat pump rebate eligibility explained.

🔍

Furnace Filter MERV Rating Guide MERV 8 vs 11 vs 13—higher isn't always better. High-MERV filters restrict airflow and strain the blower unless the ductwork was designed for the pressure drop.

🛁

Radiator Cold at Top or Bottom Cold top = trapped air (bleed it). Cold bottom = sludge buildup (needs power flushing). Understanding hydronic heating maintenance.

📉

Boiler Losing Pressure: Leak Diagnosis Pressure relief valve discharge, hidden pipe leaks under floors, or expansion vessel failure—systematically finding pressure loss in hydronic systems.

🧊

Heat Pump Covered in Ice: Normal or Not? Light frost during defrost cycle is normal—solid ice block means failed defrost control board, low refrigerant, or bad reversing valve. When to call for service.

❄️

Heat Pump Blowing Cold Air in Winter Defrost cycle produces temporary cool air—but constant cold means reversing valve stuck in cooling mode or compressor not running on heat call.

🏔️

Cold Climate Heat Pumps: Below Zero Performance Mitsubishi Hyper-Heat, Carrier Greenspeed, and other cold-climate units that deliver full capacity at -13°F. Backup heat strip sizing and when dual-fuel makes sense.

💨

Duct Leakage: The 20-30% Energy Loss Typical homes lose 20-30% of conditioned air through duct leaks in attic and crawlspace. Aeroseal vs manual mastic sealing—cost and effectiveness compared.

🏠

Uneven Heating & Cooling Between Rooms Dampers, register adjustment, and return air balancing. The upstairs-is-always-hotter problem and why closing too many registers increases static pressure and kills blowers.

🧹

Air Duct Cleaning: Scam or Necessary? EPA and NADCA guidelines—when duct cleaning is warranted (mold, vermin infestation, construction debris) vs when it's an upsell. The $99 bait-and-switch warning.

🔄

Insufficient Return Air: Symptoms & Fixes Doors slamming shut when system runs, whistling at return grille, and high static pressure. Adding return ducts or transfer grilles for balanced airflow.

🌡️

Thermostat Not Communicating With HVAC Dead batteries, tripped float switch cutting common wire, or C-wire missing for smart thermostats. Checking voltage at the thermostat before replacing it.

🏠

Smart Thermostat C-Wire Requirements Nest, Ecobee, and other smart thermostats need continuous power. C-wire alternatives: power extender kits, repurposing G-wire, or running new thermostat cable.

🏘️

Zoned HVAC: Dampers & Multi-Zone Control Motorized dampers, zone control boards, and bypass dampers. Why improperly designed zoning causes frozen coils and compressor failure.

💧

High Indoor Humidity: HVAC Solutions AC removes humidity as a byproduct of cooling—but an oversized unit short cycles and doesn't dehumidify. Whole-house dehumidifier vs portable units.

🌵

Low Winter Humidity & Whole-House Humidifiers Bypass vs steam humidifiers, hardwood floor cracking, and static electricity. Maintaining 30-50% RH for health and comfort.

🦠

Mold in HVAC System: Remediation Guide Moldy smell when AC runs means microbial growth on evaporator coil or in ductwork. UV-C light installation on coils and when professional remediation is required.

🌬️

Whole-House Air Purifier vs Portable Units Electronic air cleaners, media filters, and UV-C systems integrated into ductwork. MERV 13+ media cabinets vs HEPA bypass systems—what removes viruses, smoke, and allergens.