HVAC Repair FAQ

The most common reasons your HVAC won't turn on, in order of likelihood:

1. Thermostat issue — Dead batteries, wrong mode setting (OFF instead of HEAT/COOL), or a tripped schedule. Check batteries first, then verify the mode and temperature settings. 2. Tripped circuit breaker — HVAC systems usually have two breakers (indoor and outdoor units). Check your electrical panel for any breakers in the middle position. Flip fully OFF, wait 30 seconds, then ON. 3. Clogged air filter — A severely dirty filter can trigger the safety switch and shut the system down. Pull the filter and check if you can see light through it. 4. Safety switch triggered — The furnace door panel has a push-button safety switch. If the panel is loose or removed, the system won't run. 5. Blown fuse on control board — A low-voltage fuse on the furnace control board can blow from a wiring short. This requires opening the furnace panel to inspect.

If none of these solve it, you likely need a technician for a deeper electrical or component diagnosis.

Filter change frequency depends on the type of filter and your home conditions:

- 1-inch fiberglass filters: Every 30 days - 1-inch pleated filters: Every 60-90 days - 4-inch pleated filters: Every 6-12 months - Washable/reusable filters: Clean monthly

Change more frequently if you have: - Pets (especially dogs and cats that shed) - Allergies or asthma sufferers in the home - Recent construction or renovation nearby - Dusty area or near unpaved roads - Multiple occupants

A good rule of thumb: check your filter monthly. Hold it up to light — if you can't see through it, replace it regardless of how long it's been. A clogged filter is the #1 cause of preventable HVAC service calls and can lead to frozen coils, overheating, and system failure.

If the AC is running but not producing cold air, check these in order:

1. Thermostat setting — Make sure it's set to COOL (not just fan ON) and the target temperature is below room temp. 2. Dirty air filter — A clogged filter restricts airflow over the evaporator coil, reducing cooling capacity dramatically. 3. Dirty outdoor condenser — Leaves, dirt, and debris on the condenser fins block heat rejection. Hose it off from inside out. 4. Frozen evaporator coil — Check the indoor coil for ice. If frozen, switch to FAN ONLY for 2-4 hours to thaw, then replace the filter and try again. 5. Blocked vents — Walk the house and confirm all supply and return vents are open and unobstructed. 6. Low refrigerant — If all the above checks out, you likely have a refrigerant leak. Only a licensed technician can diagnose and repair this.

The most common DIY-fixable causes are dirty filters and dirty condenser coils. If cleaning both doesn't restore cooling within 24 hours, call a pro.

Typical HVAC repair costs (parts and labor):

Common repairs: - Diagnostic/service call: $75-150 (often credited toward repair) - Capacitor replacement: $150-300 - Igniter/flame sensor: $150-300 - Thermostat replacement: $150-400 - Blower motor: $300-600 - Refrigerant recharge: $200-500 - Condensate drain clearing: $75-200

Major repairs: - Control board: $200-600 - Compressor: $1,500-3,000 - Heat exchanger: $1,500-3,500 - Evaporator coil: $800-2,000

Factors that affect cost: Your location, time of year (emergency summer AC calls cost more), brand of equipment, and whether it's during or after business hours. Always get 2-3 quotes for non-emergency repairs. A repair that's 50% or more of replacement cost on a system over 10 years old usually means replacement is the better investment.

Most furnaces have a small LED light on the control board that blinks in patterns to indicate status or errors. The patterns vary by manufacturer, but common codes include:

- Steady ON: Normal operation, no fault - 1 blink: Ignition failure or no flame detected - 2 blinks: Pressure switch stuck open (venting issue) - 3 blinks: Pressure switch stuck closed - 4 blinks: Open high limit switch (system overheating, often caused by dirty filter) - 5 blinks: Flame sensed without gas valve call (dangerous, call a pro) - Rapid blinking: System lockout, needs manual reset

To read your specific codes: Open the lower furnace panel and look for the LED. A code chart is usually printed on a sticker inside the panel door. Count the number of blinks in each sequence, then match to the chart.

Important: Write down the exact code before resetting the system. Share this code with your technician — it dramatically speeds up diagnosis and can save you money on the service call.

Common HVAC sounds and what they indicate:

- Rattling: Loose screws, panels, or ductwork. Usually harmless — tighten accessible fasteners. - Squealing/screeching: Worn belt (older systems) or failing motor bearings. Turn off the system to prevent further damage and call a tech. - Banging at startup: Could be duct expansion (harmless) or delayed ignition (dangerous). If it's from the furnace, not the ducts, call a pro immediately. - Clicking: Normal at startup/shutdown. Continuous clicking may indicate a failing relay or control board. - Humming: Normal for a running system. Loud humming with no airflow means a seized blower motor or bad capacitor. - Buzzing: Electrical issue — could be a contactor, capacitor, or loose wiring. Call a pro. - Gurgling/bubbling: Refrigerant leak or condensate drain issue. - Hissing: Refrigerant leak (at the outdoor unit) or air leak in ductwork.

Rule of thumb: Sudden new sounds warrant investigation. Sounds that get progressively louder mean the problem is getting worse — address it before it becomes a bigger repair.

Different HVAC smells indicate different problems:

- Dusty/burning on first start of season: Normal. Dust accumulated on the heat exchanger is burning off. Should clear in 15-30 minutes. Open windows to ventilate. - Persistent burning: Overheating motor or electrical component. Turn system OFF immediately and call a technician. - Electrical/plastic smell: Wiring issue or melting component. Turn OFF immediately — fire risk. - Musty/moldy: Mold growing in ductwork or on the evaporator coil. Not an emergency but should be addressed — can cause respiratory issues. Often resolved by UV light installation or coil cleaning. - Rotten eggs/sulfur: GAS LEAK. Leave the house immediately. Do not flip any switches or use electronics. Call your gas company from outside. - Chemical/formaldehyde: Possible cracked heat exchanger allowing combustion gases into your air supply. Carbon monoxide risk. Shut off and call for emergency service. - Sewage smell: Dried-out drain trap or sewer gas entering through the condensate line. Pour water into the drain trap.

Safety rule: If you smell gas or electrical burning, shut off the system and address it as an emergency.

Consider replacement when:

- Age + cost: System is 15+ years old AND the repair exceeds 50% of replacement cost - The $5,000 rule: Multiply the repair cost by the system's age. If the result exceeds $5,000, replace. Example: $400 repair x 14 years = $5,600 — time to replace. - Frequent breakdowns: If you've had 3+ repairs in the past 2 years, the system is declining - R-22 refrigerant: If your AC uses R-22 (Freon), it's being phased out and increasingly expensive. Replacement with an R-410A system is the long-term answer. - Rising energy bills: Old systems lose efficiency over time. A new system can be 20-40% more efficient.

Average system lifespans: - Central air conditioner: 15-20 years - Gas furnace: 15-25 years - Heat pump: 10-15 years

Average replacement costs: - Central AC only: $3,500-7,500 - Furnace only: $2,500-6,000 - Complete system (AC + furnace): $5,000-12,000 - Heat pump system: $4,000-8,000

New systems come with 5-10 year warranties, better comfort, and significant energy savings.

DIY-safe repairs (no special tools or training needed): - Replace air filters - Replace thermostat batteries - Reset tripped circuit breakers - Clean supply and return vents - Clear area around indoor and outdoor units - Hose off the outdoor condenser - Pour vinegar down the condensate drain line - Check and adjust thermostat settings - Relight a pilot light (following manufacturer instructions) - Verify the gas valve is in the ON position (visual check only)

Call a professional for: - Anything involving refrigerant (legally requires EPA certification) - Gas line issues or gas leak suspicion - Electrical work beyond breaker resets - Compressor or motor replacement - Heat exchanger inspection or replacement - Ductwork modification - Any repair on a system still under warranty (DIY can void it) - Repeated breaker trips (indicates a larger electrical problem)

The line is simple: if it involves gas, refrigerant, or internal electrical components, call a pro. Everything else on the outside of the system is generally safe for DIY.

The standard recommendation is twice per year:

- Spring (March-May): AC/cooling tune-up before summer - Fall (September-November): Heating tune-up before winter

What a professional maintenance visit includes: - Inspect and clean all components - Check refrigerant levels and pressure - Test electrical connections and tighten as needed - Lubricate moving parts - Check all safety controls - Measure airflow and temperature differentials - Inspect heat exchanger for cracks (critical safety check) - Clean condensate drain - Check thermostat calibration

Cost: $75-200 per visit, or $150-300/year for a maintenance plan that covers both visits.

Between professional visits, DIY maintenance includes: changing filters every 1-3 months, keeping the outdoor unit clean and clear, clearing the condensate drain line quarterly, and listening for unusual sounds.

Regular maintenance extends system life by 5-10 years, maintains efficiency, catches small problems before they become expensive repairs, and keeps your warranty valid (many manufacturers require annual maintenance).

A blank thermostat screen has several possible causes:

1. Dead batteries (most common): Most thermostats use AA or AAA batteries. Replace them and the display should come back immediately. 2. Tripped circuit breaker: The HVAC breaker powers the transformer that feeds the thermostat. Check your breaker panel. 3. Blown low-voltage fuse: The furnace control board has a 3-5 amp fuse that can blow from a wiring short. This requires opening the furnace panel to check. 4. Tripped float switch: If the AC condensate drain is clogged, the safety float switch cuts power to prevent water damage. Check for water around the indoor unit. 5. Bad transformer: The 24V transformer converts household power for the thermostat circuit. If it fails, the thermostat gets no power. A technician can test this. 6. Wiring issue: A loose or disconnected wire at the thermostat or furnace can break the circuit.

Start with batteries. If your thermostat is hardwired (no battery compartment), check the breaker. If neither works, the issue is likely the transformer, fuse, or wiring — time to call a tech.

Short cycling — when the system runs for a few minutes then shuts off repeatedly — has several causes:

- Dirty air filter: The #1 cause. Restricted airflow causes overheating, triggering the high limit switch. Replace the filter. - Oversized system: An HVAC system that's too large for the space cools or heats quickly, then shuts off before a full cycle. This is a design/installation issue. - Thermostat problems: A thermostat in direct sunlight, near a heat source, or in a drafty location reads incorrect temperatures, causing frequent cycling. - Low refrigerant: Causes the system to struggle and trigger safety shutoffs. Needs a pro. - Frozen evaporator coil: Ice on the coil causes temperature swings that trigger cycling. Thaw by running FAN ONLY. - Failing compressor: An aging compressor that overheats and shuts down on its thermal overload. - Electrical issues: Loose wiring, failing capacitor, or bad contactor.

Short cycling wastes energy, increases wear on components (especially the compressor), and reduces comfort. If replacing the filter doesn't fix it, have a technician diagnose the root cause before the cycling damages expensive components.

If you find ice on your indoor evaporator coil, follow these steps:

1. Turn the system to FAN ONLY (not OFF — the fan helps melt the ice faster) 2. Place towels around the indoor unit to catch meltwater 3. Wait 2-4 hours until the ice is completely melted 4. While waiting, replace the air filter with a new one 5. Check that all vents throughout the house are open and unobstructed 6. Once thawed, turn the system back to COOL and monitor

If it freezes again within 24 hours, you likely have a refrigerant leak, which only a licensed technician can diagnose and repair. Adding refrigerant without fixing the leak is a temporary fix that will need repeating.

Common causes of frozen coils: - Dirty air filter (most common, easy DIY fix) - Blocked or closed vents - Dirty evaporator coil (needs professional cleaning) - Low refrigerant from a leak (needs professional repair) - Blower motor not running at full speed - Running AC when outdoor temperature is below 60F

Never chip or scrape ice off the coil — you can damage the fragile fins and cause a refrigerant leak.

If you smell rotten eggs or sulfur near your furnace, this indicates a potential gas leak. Follow these steps immediately:

1. Do NOT flip any switches, light matches, or use electronics near the smell 2. Do NOT try to find or fix the leak yourself 3. Leave the house immediately — take everyone including pets 4. Once safely outside, call your gas utility company's emergency line (it's on your bill, or call 911) 5. Do not re-enter the home until the gas company clears it as safe

Natural gas is odorless — the rotten egg smell is mercaptan, an additive specifically so you can detect leaks. Even a faint smell should be taken seriously.

After the gas company clears your home: - Have an HVAC technician inspect the furnace before restarting it - Check that the gas valve connections are tight - Consider installing natural gas detectors near the furnace and in bedrooms

A slight gas smell when the furnace first ignites is sometimes normal (unburned gas before ignition). But if the smell persists, is strong, or occurs when the furnace isn't running, treat it as an emergency.

Carbon monoxide is a separate, equally dangerous concern. Install CO detectors on every level of your home and near bedrooms. A cracked heat exchanger can leak CO without any detectable smell.

It depends on the repair and your warranty terms:

Generally safe (won't void warranty): - Replacing air filters - Replacing thermostat batteries - Resetting circuit breakers - Cleaning vents and registers - Hosing off the outdoor unit - Clearing condensate drain lines - Basic thermostat troubleshooting

May void warranty: - Opening the sealed refrigerant system - Replacing internal electrical components - Modifying ductwork connections to the unit - Using non-approved replacement parts - Any repair that a manufacturer determines caused subsequent damage

Key warranty requirements that are commonly missed: - Annual professional maintenance (most manufacturers require this to keep the warranty valid) - Registration within 60-90 days of installation (extends warranty from 5 to 10 years for many brands) - Using a licensed HVAC contractor for installation

If your system is less than 5 years old, always check your warranty before attempting any repair beyond basic maintenance. The cost of a service call ($75-150) is worth it to protect a warranty that could cover a $2,000+ compressor replacement.