ASE G1 Auto Maintenance and Light RepairHeating and Air Conditioning (HVAC)Hard
A customer complains that their vehicle's heater only blows cool air, even after the engine has reached operating temperature. The coolant level is full, and the engine temperature gauge reads normal. What is the MOST likely cause of this issue?
- AAir trapped in the heater core.
- BA malfunctioning AC compressor.
- CA stuck-open thermostat.
- DA faulty blower motor.
Show answer & explanationAnswer & explanation
Correct answer: A. Air trapped in the heater core.
Even with a full coolant level, air pockets can become trapped in the heater core, preventing hot coolant from circulating through it. This results in poor heat transfer to the cabin air, leading to cool air from the vents.
Why the other options are wrong
- B. A malfunctioning AC compressor would affect the air conditioning, not the heating function, as the heater core uses engine coolant for heat.
- C. A stuck-open thermostat would cause the engine to run cooler than normal, which would be indicated by a low engine temperature gauge reading, contradicting the 'normal' reading in the stem.
- D. A faulty blower motor would prevent any air from blowing, or reduce its volume, not specifically cause cool air when heat is requested.
Air in Heater Core
Air trapped in the heater core prevents hot engine coolant from circulating, leading to insufficient or no heat being transferred to the vehicle's cabin.
- Often caused by incomplete coolant system bleeding.
- Creates a 'bubble' that blocks coolant flow.
- Results in cold or lukewarm air from heater vents.
- Engine temperature gauge may read normal.
Memory trick: Coolant's there, but air's in the way, blocking the heat, ruining the day.