Heating and Cooling Flashcards
7 cards from real ASE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Heating and Cooling flashcards as text
The engine is at normal temperature and both heater hoses are hot, but the heater only blows cold air. What is the most likely cause?
Answer: Blend door stuck in the cold position
Two hot hoses show coolant is flowing through the heater core, so the fault is in air delivery, such as a stuck blend door.
The heater inlet hose is hot but the outlet hose is much cooler, and heat output is poor. This most likely indicates:
Answer: A restricted or plugged heater core
A large temperature drop across the heater core means coolant flow through it is restricted.
A blower motor works only on the high speed setting. What is the most likely cause?
Answer: Open blower motor resistor
High speed usually bypasses the resistor, so an open resistor kills the lower speeds only.
After a coolant flush, the heater blows cold at idle but warms up when the engine is revved. What is the most likely cause?
Answer: Air trapped in the cooling system
An air pocket blocks low-speed coolant flow through the heater core, so the system must be bled properly.
An engine overheats at idle and in slow traffic but stays normal at highway speed. What is the most likely cause?
Answer: Inoperative electric cooling fan
At highway speed ram air cools the radiator, so overheating only at low speed points to a cooling fan problem.
An engine stays at normal temperature at idle but overheats at sustained highway speed. Which cause is most likely?
Answer: Partially restricted radiator core
Under high load a partly plugged radiator cannot reject enough heat, even though it keeps up at idle.
On vehicles that have one, what does the heater control valve do?
Answer: Controls coolant flow to the heater core
The heater control valve opens or restricts coolant flow to the heater core to control heat output.