HVAC Control Systems 403b Flashcards
What type of controls are used by the driver to turn the system ON, and adjust air temperature, airflow direction and velocity?
active
What type of controls regulate the flow of air conditioning refrigerant or heater coolant without driver input?
passive
What type of controls may prevent or support system functions?
supplemental
The blower speed switch has three ON positions to control blower fan speed and regulate the HVAC system air velocity, which is measured in:
CFM (cubic feet per minute)
The engine coolant water valve is a passive control that allows the operator to set the amount of hot engine coolant that will pass through the heater core.
T/F
false; The engine coolant water valve is an active control.
A seized open engine coolant water valve will cause the truck cab to remain very warm even when the truck’s air conditioning is operating, when warm spring and summer weather occurs.
T/F
true; This is a major problem every spring in northern climates.
A 12-volt electromagnetic clutch coil is indicated by a:
black lead wire
The first passive control in the electrical circuit that energizes the compressor electromagnetic clutch is a:
thermostatic switch
When the air conditioning system contains a fixed expansion tube and an accumulator, the thermostatic switch may be replaced with a:
clutch cycling switch
Refrigerant low pressure sensing switches are used on thermostatic expansion valve equipped air conditioning systems as a low ambient temperature protection switches.
T/F
true; The ambient temperature switch will protect the air conditioning
compressor from operating with very low refrigerant pressures and a lack of oil circulation.
The pressure settings of the high pressure switch must be adjusted ____ ____ the settings of the refrigerant’s pressure relief valve or fusible plug.
lower than
The Binary™ switch acts like a _______ _________ switch.
3
- low-pressure
- high-pressure
- ambient temperature
How many functions does the Trinary™ pressure switch perform to monitor and control refrigerant pressure inside the air conditioning system?
three
List the two (2) devices used to control refrigerant flow into the evaporator core.
- thermal expansion valve
- fixed orifice tube
What electrical device is used in HVAC systems to control fan or blower motor speed?
resistor
List the two (2) types of blower wheels that are used in HVAC systems.
- single entry blower wheels
- double entry blower wheels
A heater system uses ______ _______ to carry excess engine heat energy to warm the cab air.
engine coolant
List the three (3) inputs of an air conditioning management system.
- high pressure switch
- low pressure switch
- evaporator thermostatic switch
List the three (3) outputs of an automatic temperature control system.
- the heater water control valve
- the fan blower motor
- the air conditioning system compressor
When the maximum cooling setting is chosen on the control panel, the air
conditioning switch is turned to the _________________ position. The fresh air
door is set on the __________________ position. The temperature setting is turned
towards the __________________________ setting.
on, recirculation, blue
When the maximum heating setting is chosen on the control panel, the air
conditioning switch is turned to the _________________ position. The
temperature setting is turned towards the _______________ setting.
off, red
When the maximum defrost setting is chosen on the control panel, the airflow
direction is set towards the _______________ position. The air conditioning
switch is turned to the OFF position. To remove the mist from the windshield,
the air conditioning compressor’s electromagnetic clutch is ________________
and the evaporator will cool and _________________ the recirculated cab air.
defrost, engaged, dehumidify
A manual climate control HVAC system is called a _____________________
_______________________ system.
temperature blend air door
The truck’s _______________ must be operating if the sleeper compartment is to be
heated or cooled.
engine
When the cooling function on the control panel is chosen, the electrically controlled
refrigerant __________ _________ is opened and refrigerant is
allowed to pass through the sleeper compartment’s ____________
________ _________ and into the evaporator core.
solenoid valve;
thermal expansion valve
