Property · Improve

HVAC Diagnosis Live Matrix

A dead AC, heater problem, weak heat, or furnace lockout is not automatically a system replacement. Start with what the homeowner saw, then make the quote show evidence.

Map HVAC symptoms to likely cheap fixes, safety stops, repair scopes, and replacement-level failures before accepting a sales quote.

Start the tool How this estimate works Build decision packet Not sure where to start?

Plain English

My AC or heat is not working. What should I check before replacing it?

This starts with symptoms and helps you ask what the tech proved.

Start here: Pick what you see at home: no cooling, weak air, ice, drain trouble, or heat trouble.

Estimate inputs

What you see at homeThermostat callIndoor blower behaviorOutdoor unit behavior, if cooling or heat pumpGas furnace patternElectric heat / sequencer patternBreaker statusDrain float switch / water safetyA clogged condensate drain can shut the system off before anything expensive is broken.Technician quoted a control boardBoard replacement can be real, but it should not be the first guess before power, thermostat, safeties, sensors, relays, and wiring are checked.Flame sensor already cleaned/testedThermostat was recently replaced or reprogrammedFilter is dirty or airflow seems weakCapacitor ageyrsSystem ageyrsWhat the contractor is saying

Result

1 service-call paths before replacement

Replacement pressure: Low
Homeowner symptom: cooling dead
System age: 12 years
Thermostat signal: calls cool
Indoor blower: runs

Flags to check

No immediate replacement-level proof from these inputs. Ask for diagnostics before sales scope.

Options to ask for

Capacitor, contactor, or condenser fan motor

Cheap failures can make AC look dead or make a compressor look worse than it is.

A bad capacitor can cause humming, no fan spin, hard starting, or compressor start failure.
A bad contactor can keep the outdoor unit silent even when the thermostat calls.
A failed condenser fan can overheat the compressor and mimic larger trouble.

Pushback: Ask: what were the capacitor microfarads, contactor voltage, amp draw, and fan motor findings?

Start from what the homeowner can actually know: what happened, what changed recently, what the thermostat/outdoor unit/blower did, and what the technician claimed.

This is a homeowner matrix for asking better questions, not instructions to bypass safety switches or work inside energized equipment.

If there is gas smell, carbon monoxide alarm, flame rollout, burning smell, melted wiring, or repeated breaker trips, stop using the system and call qualified help.

Assumptions

Use symptoms, recent history, and what the technician said. You do not need to know the failed part.
Do not open electrical cabinets unless qualified. Capacitors can hold dangerous charge.
Gas smell, carbon monoxide alarm, flame rollout, cracked heat exchanger, burning smell, melted wiring, or repeated breaker trips are stop conditions. Shut the system down and call qualified help.
This is a homeowner pushback checklist, not a live electrical diagnostic procedure.
Identify the heat type first: gas furnace, electric furnace or air handler heat strips, heat pump with auxiliary heat, boiler, or another setup.
A breaker that trips immediately, burning smell, melted wire, or shorted compressor needs a qualified technician.

Decision check

Before you act on the number

The output is useful only if it survives the missing-scope, fragile-assumption, and next-step check.

Mistake check

Buying the replacement story before scope, diagnosis, ducts, warranty, or repair economics are clear.

What people forget

Cheaper service-call causes
Ducts, returns, zoning, and comfort distribution
Partial replacement or repair options
Rebate eligibility and payback limits

What makes it go bad

The quote replaces good parts
A new system still leaves comfort problems
The low bid excludes duct, electrical, permit, or warranty work

What to do next

Owners usually start with symptoms or repair-vs-replace, then compare repair, partial replacement, full replacement, and duct options.

Use the decision packet to compare scopes, missing measurements, warranty terms, and cheaper causes ruled out.

Cheap failures can look like replacement-level failures

A failed capacitor, contactor, thermostat signal, drain float switch, dirty filter, iced coil, condenser fan motor, blower motor, flame sensor, limit switch, sequencer, heat strip relay, or thermostat wiring issue can make HVAC equipment look dead. Those are service-call problems before they are replacement problems.

Bad capacitor: outdoor unit may hum, fan may not spin, or compressor may fail to start.
Bad contactor: outdoor unit may stay silent even when the thermostat calls for cooling.
Blower or limit problem: the furnace or air handler may shut down, overheat, or never move enough air.
Dirty flame sensor: gas burner may light briefly, then shut down because the board does not prove flame.
Electric sequencer or relay failure: blower may run while heat strips fail to energize, or only some stages heat.
Thermostat or low-voltage issue: the equipment may be fine but never receives the correct call.
Float switch: a clogged condensate drain can shut the system off to prevent water damage.
Dirty filter or iced coil: airflow problems can make the system shut down or blow warm air.

When replacement enters the conversation

Replacement becomes more serious when the compressor is confirmed electrically shorted or mechanically locked, the heat exchanger is unsafe, the coil is leaking and old, the refrigerant path is expensive, electric heat has repeated high-current failures, or the system has multiple failures near end of life.