HVAC Review Flashcards
The terminal labeled ‘W2’ on a seven-wire thermostat is used to connect to what?
Second stage heating
What is the ‘R’ terminal?
24V supply
What Is the ‘W’ terminal for?
Heat
What is the ‘G’ terminal for?
The fan
What is the ‘Y’ terminal for?
Cooling
What is the ‘C’ terminal for?
Common
Heating systems are rated according the amount of what?
Energy input into the system
True or false
A t stat is a controlling device that provides feedback to a load device
True
Convection is heat transfer in which form?
Through air
Four reasons for automatic control
Comfort, economy, convenience, safety
Cecs
What is a closed loop system?
A system that uses feedback to make a process automatic
What is high limit control generally set at?
80 - 100 degrees celsius
What are the typical fan settings
Fan on 49 - 60
Fan off 32 -38
Differential 17-22
List three types of contacts used in thermostats
Mercury ( most popular)
Spring activated or snap action exposed
Glass enclosed magnet and armature snap acting
How is the anticipator connected with the thermostat in a heating system?
In series
How is the anticipator connected with the thermostat in a cooling system?
In parallel
Where would a manual override switch be installed in a heating system?
In parallel with he fan control switch
What is a common name for a manual override switch?
Summer switch
What are the 3 main types of bi metallic temp sensing devices?
Spiral type
Strip type
Disc type
What is the open circuit voltage of a thermocouple?
26-32 mVdc
What is the closed circuit voltage of a thermocouple?
7.5-15 mVdc
What does hrv stand for?
Heat recovery ventilator
High efficiency furnaces are also know as what?
Condensing furnaces
What does afue stand for?
Annual fuel utilization fee
What is the afue of a mid efficiency furnace?
80 -90%
Gat device proves the operation of the cab?
The air prove controller
List the 3 types of electronic ignition systems may be used with efficient furnaces
Hot Surface ignition
Direct Spark
Intermittent pilot
True or false
The combustion air prove controller is a normally open pressure switch
False
Normally closed
Acts on a negative air pressure ( suction pulls it in to close contacts)
List four types of humidifiers that can be installed on furnaces
Standing water absorbent
Rotating drum
Rotating disk
Flow through
Another term for hot water heat is?
Hydronic heat
List some Common terminal heat exchange units
Radiators, unit heaters, radiant panels
What is the maximum capacity for a class 2 transformer
100 va
List the 3 types of ignition devices that may be used for hot water heating systems
Direct spark ignition
Hot surface ignition
Standing pilot flame
List the five main components of a cooling system
Condenser coil Evaporator coil Refrigerant Compressor Refrigerant control valve (TX valve)
What is the purpose of the evapourator
Absorbs heat from the air blowing through its fins
What is the purpose of the condenser in a cooling system?
To cool the compressed hot refrigerant vapour
List 3 types of rcv’s
Thermostatic expansion valve
Thermal electric valve
Automatic expansion valve
Adding a cooling system to an existing residential furnace requires the addition of what 3 mechanical components?
Evapourator
2 speed blower
Compressor and condenser
List 3 major sections of an HVAC system
Heating
Cooling
Ventilation
True or false
A flame proving circuit has an approximate circuit current value of 1.5 to 4 micro amps
True
In a cooling system a high pressure sensor is connected to the discharge side of the compressor. This high pressure sensor is a normally open pressure switch
True
True or false
The location of air conditioning equipment a disconnect means within site and 1m from equipment
False
Within 3
28-604
A direct fired MUAU has how many heat exchangers?
None motha fucka
List 3 reasons for heat trace
To melt ice and snow
Keep pipes and valves from freezing
Keep liquids inside of pipes at a maintained temp
List the four main types of heat tracing systems
Self regulating variable resisting
Series fixed
Parallel fixed
Skin effect
What is an AHU?
Air handling unit
What is an RTU?
Roof top unit
What is an MUA?
Make up air unit
1 unit that replaces exhausted air
What is a VAV?
Variable air volume box
In a cooling system, the high pressure sensor is a normally open pressure switch.
True or false
False
It is normally closed
