ASE Heating and Cooling 3

Question 1

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?

Accepted Answer

Blend door stuck in the cold position

Answer

Two hot hoses show coolant is flowing through the heater core, so the fault is in air delivery, such as a stuck blend door.

Question 2

The heater inlet hose is hot but the outlet hose is much cooler, and heat output is poor. This most likely indicates:

Accepted Answer

A restricted or plugged heater core

Answer

A large temperature drop across the heater core means coolant flow through it is restricted.

Question 3

A blower motor works only on the high speed setting. What is the most likely cause?

Accepted Answer

Open blower motor resistor

Answer

High speed usually bypasses the resistor, so an open resistor kills the lower speeds only.

Question 4

After a coolant flush, the heater blows cold at idle but warms up when the engine is revved. What is the most likely cause?

Accepted Answer

Air trapped in the cooling system

Answer

An air pocket blocks low-speed coolant flow through the heater core, so the system must be bled properly.

Question 5

An engine overheats at idle and in slow traffic but stays normal at highway speed. What is the most likely cause?

Accepted Answer

Inoperative electric cooling fan

Answer

At highway speed ram air cools the radiator, so overheating only at low speed points to a cooling fan problem.

ASE - Automotive Service Excellence Certified Tech Practice Test