When diagnosing poor heater performance, which of the following would cause reduced heat output?

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Multiple choice — select the best answer

AAn overcharging alternator
BA high coolant level
CA thermostat that is stuck open
DA thermostat that is stuck closed

✓ Correct answer: C. A thermostat that is stuck open A stuck open thermostat prevents the engine from reaching proper operating temperature, which means the coolant going to the heater core isn't hot enough to produce adequate heat.

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When diagnosing poor heater performance, which of the following would cause reduced heat output?

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