CSLB C-20 HVAC ContractorHeating SystemsEasy
A homeowner reports a musty odor and headaches when the furnace runs. A technician suspects a cracked heat exchanger. Which safety instrument should be used FIRST to confirm this hazard before disassembling the furnace?
- AClamp-on ammeter at the blower motor
- BManometer to check gas pressure
- CCombustion analyzer/CO detector at the supply registers
- DRefrigerant leak detector near the coil
Show answer & explanationAnswer & explanation
Correct answer: C. Combustion analyzer/CO detector at the supply registers
A cracked heat exchanger allows flue gases containing carbon monoxide to mix with the circulating air stream. Testing supply air with a CO detector or combustion analyzer is the standard field verification before physical inspection or disassembly.
Why the other options are wrong
- A. Amperage relates to motor condition, not combustion gas leakage.
- B. Gas pressure relates to burner input, not exchanger integrity.
- D. Refrigerant detectors do not sense combustion byproducts.
Cracked Heat Exchanger
A failure in the metal barrier separating combustion gases from circulating air, allowing carbon monoxide to enter the home's airstream.
- CO is odorless and colorless, making detection instruments essential
- Testing supply air CO levels is a standard diagnostic step
- A confirmed crack requires furnace shutdown and exchanger replacement
Memory trick: Crack in the exchanger, CO comes to visit — test before you twist (wrenches).