MICHIGAN MECHANIC EXAMS SCRIPT ANSWERS
AND QUESTIONS SET A+
✔✔Purpose of the thermostat - ✔✔The purpose of the thermostat is to trap the coolant
in the engine until it reaches it operating temperature
✔✔Cause of low heater output - ✔✔Low coolant level, clogged heater core, leaking
heater core
✔✔Heater core hose routing - ✔✔The supply hose from the heater core should run from
the closed side of the thermostat to the heater core and the return hose should run from
the heater core to the engine
✔✔Heater core operation - ✔✔The blower motor blows air through the heater core fins
and is warmed through the principle of conduction
✔✔Heater control valve purpose - ✔✔This valve controls the flow of the coolant to the
heater core to control the temperature of the air desired by the operator
✔✔Radiator cap testing - ✔✔To test pressure test it using an adapter and a coolant
pressure tester and the value marked on the pressure cap
✔✔Reciever drier purpose - ✔✔May contain a filter or strainer to catch and trap foreign
particles and dirt
✔✔Reciever drier location - ✔✔Located on the high side of the system between the
condenser and the evaporator
✔✔Ambient temperature switch purpose - ✔✔Monitors temperature by increasing or
decreasing with resistance as temperature changes
✔✔Symptoms of a failing ambient temperature switch - ✔✔A bad temperature switch
could cause an inoperative clutch or input problems
, ✔✔Orifice expansion tube operation - ✔✔Has a valve that can vary the size of the
opening to allow more or less liquid refrigerant through to the evaporator
✔✔Orifice expansion tube purpose - ✔✔High pressure liquid enters, low pressure liquid
leaves
✔✔Purpose of a compressor - ✔✔Low pressure gas enters and high pressure gas
leaves
✔✔Symptoms of a failing compressor - ✔✔Pressures are going to be equal
✔✔Purpose of a condenser - ✔✔Low pressure gas enters and high pressure gas
leaves
✔✔Symptoms of a failing condenser - ✔✔Symptoms of failure or restriction are a high
high-side discharge of pressures
✔✔Purpose of a evaporator - ✔✔Low pressure liquid changes into low pressure gas
✔✔Symptoms of a failing evaporator - ✔✔Symptoms of a failed component could be a
leak, sniffer test required
✔✔Purpose of a fixed orifice tube - ✔✔High pressure liquid enters, low pressure liquid
leaves
✔✔Symptoms of a clogged orifice tube - ✔✔Frost forming around the restricted area
✔✔Typical cause of a clogged orfice tube - ✔✔A clogged orifice tube is typically caused
by compressor failure
✔✔R-12 background - ✔✔R-12 is Freon and it destroys the ozone layer due process of
releasing CFCS into the air
✔✔What replaced R-12 - ✔✔R-134a
✔✔What replaced R134a - ✔✔R1234yf
✔✔What is operating pressure of low side pressure? - ✔✔Low pressure should be
between 20psi-40psi
✔✔What is operating pressure of high side pressure? - ✔✔High pressure should be
between 170psi-230psi
AND QUESTIONS SET A+
✔✔Purpose of the thermostat - ✔✔The purpose of the thermostat is to trap the coolant
in the engine until it reaches it operating temperature
✔✔Cause of low heater output - ✔✔Low coolant level, clogged heater core, leaking
heater core
✔✔Heater core hose routing - ✔✔The supply hose from the heater core should run from
the closed side of the thermostat to the heater core and the return hose should run from
the heater core to the engine
✔✔Heater core operation - ✔✔The blower motor blows air through the heater core fins
and is warmed through the principle of conduction
✔✔Heater control valve purpose - ✔✔This valve controls the flow of the coolant to the
heater core to control the temperature of the air desired by the operator
✔✔Radiator cap testing - ✔✔To test pressure test it using an adapter and a coolant
pressure tester and the value marked on the pressure cap
✔✔Reciever drier purpose - ✔✔May contain a filter or strainer to catch and trap foreign
particles and dirt
✔✔Reciever drier location - ✔✔Located on the high side of the system between the
condenser and the evaporator
✔✔Ambient temperature switch purpose - ✔✔Monitors temperature by increasing or
decreasing with resistance as temperature changes
✔✔Symptoms of a failing ambient temperature switch - ✔✔A bad temperature switch
could cause an inoperative clutch or input problems
, ✔✔Orifice expansion tube operation - ✔✔Has a valve that can vary the size of the
opening to allow more or less liquid refrigerant through to the evaporator
✔✔Orifice expansion tube purpose - ✔✔High pressure liquid enters, low pressure liquid
leaves
✔✔Purpose of a compressor - ✔✔Low pressure gas enters and high pressure gas
leaves
✔✔Symptoms of a failing compressor - ✔✔Pressures are going to be equal
✔✔Purpose of a condenser - ✔✔Low pressure gas enters and high pressure gas
leaves
✔✔Symptoms of a failing condenser - ✔✔Symptoms of failure or restriction are a high
high-side discharge of pressures
✔✔Purpose of a evaporator - ✔✔Low pressure liquid changes into low pressure gas
✔✔Symptoms of a failing evaporator - ✔✔Symptoms of a failed component could be a
leak, sniffer test required
✔✔Purpose of a fixed orifice tube - ✔✔High pressure liquid enters, low pressure liquid
leaves
✔✔Symptoms of a clogged orifice tube - ✔✔Frost forming around the restricted area
✔✔Typical cause of a clogged orfice tube - ✔✔A clogged orifice tube is typically caused
by compressor failure
✔✔R-12 background - ✔✔R-12 is Freon and it destroys the ozone layer due process of
releasing CFCS into the air
✔✔What replaced R-12 - ✔✔R-134a
✔✔What replaced R134a - ✔✔R1234yf
✔✔What is operating pressure of low side pressure? - ✔✔Low pressure should be
between 20psi-40psi
✔✔What is operating pressure of high side pressure? - ✔✔High pressure should be
between 170psi-230psi
