[D2L] Final Review Flashcards
What is the Branch pressure of a 2 pipe Thermostat
0-20psi
What control system has ultimate authority over all building functions?
Fire Alarm
A pilot duty overload interrupts the current to the motor directly?
False, it operates indirectly to protect the motor
Two Position Thermostats are analog
False, they are digital
How do low pressure controllers usually operate?
Close on Rise/Open on Fall
On a CONSTANT CUT IN, the thermostat is adjusted by the dial on the front. what does the adjusted number change?
the adjusted value subtracts from the set point
How many conductors in a CAT 5 cable
8
Advantage of 3 pipe controller over a 2 pipe controller is….
Greater capacity and ability to control multiple actuators
An actuator controls the dampers in an HVAC unit
True
Select all positions that works floating point control (Hint: There are 3 commands) (MULTI-SELECT)
1) switch 1 - ON ; switch 2 - OFF
2) switch 1 - OFF ; switch 2 - OFF
3) switch 1 - OFF ; switch 2 - ON
4) switch 1 - ON ; switch 2 - ON
1) switch 1 - ON ; switch 2 - OFF
2) switch 1 - OFF ; switch 2 - OFF
3) switch 1 - OFF ; switch 2 - ON
What is the difference between a line duty and pilot duty overload device?
Pilot duty interrupts the control current and line duty interrupts the line current
What type of control system are relays and contactors considered?
electromechanical
What is an electronic hygroscopic sensor made of? (MULTISELECT 3)
1) nylon ribbon
2) resistance change polymer
3) golf foil grid
4) human hair
5) thin-film polymer
resistance change polymer
gold foil grid
thin-film polymer
When the High limit trips on a furnace, it kills power to what?
Gas valve
In an electronic thermostat, the length of time it takes for the control point and the setpoint to equalize is called:
Deviation
Solenoid valves are multi-directional
False, it’s digital so just on/off
Only semi-hermetic compressors that have oil pumps, use an oil failure control
True
How can you prevent damage to a solenoid coil if it is energized off its valve stem?
put a screw driver inside it
Mixed air controllers are typically set to what temperature?
50F - 60F
What do OFC’s protect in a system from insufficient lubrication?
Compressor
Why is the crankcase heater energized for the compressor during the shut down period?
Prevent oil foaming on compressor startup
What is an acceptable temperature dry bulb setpoint for a change-over thermostat?
50F – 60F
In a freezer, the Fan Delay’s job is to…
Allow water to freeze on it after a defrost prior to the fans starting up
Pick the two devices that are required for a pump-down control system (multiselect)
1) Thermostat
2) Contactor
3) Flow Controller
4) Pressure Controller
Thermostat
Pressure Controller
What type of control is a cooling thermostat considered?
Direct acting
A semiconductor relay has no moving parts, inexpensive, switch more quickly and have a longer life expectancy
True
What are the two air flows that are being mixed by an Economizer?
1) Return
2) Supply
3) Mixed
4) Outdoor
Return
Outdoor
Why do low temp refrigeration have oil return issues?
low density refrigerant suction vapour doesn’t carry oil with it as well
What is a delay on break control best suited to monitor?
Short Cycling
The condenser fan controller cycles the condenser fans in response to a discharge pressure, ambient temperature or liquid line temperature and thus maintains a minimum discharge pressure
T or F
True
When a pump down control system thermostat first calls it sends power to the LLS solenoid allowing the refrigerant to do what?
Pressure to rise throughout the system and close the pressure control
On a call for cooling what terminals will have 24V present?
G,R,Y
What is the difference between a relay and a contactors?
Relays are under 15 Amps
Contactors are over 15 Amps
For the Oil Failure Controller to operate correctly…
The crankcase pressure needs to be lower than the oil pump pressure to verify pressure difference
T or F
True
What are the 3 common types of sensors?
1) humidity
2) flow
3) pressure
4) temp
5) level
humidity
pressure
temp
A system without controller feedback is called an open loop
True
Range is the Min and Max Setting of a controller
True
What is the sequence of operation for a heating cycle in the carrier furnace from the residential heating videos?
(1) Thermostat R closes to W
(2) Inducer runs
(3) Pressure switches close
(4) HSI is energized
(5) Gas valve energized
(6) Flame signal is proven by the flame sensor
(7) Blower turns on after a determined time
(8) When the thermostat is satisfied, terminals R to W opens, inducer motor runs for additional 15 seconds, gas valve is de-energized and blower continues to run for an additional 90 seconds
determine the expected feedback signal from a 2-10vdc control in response to a 85 % demand
8.80 vdc
determine the control signal you would expect from a 20 % demand in a 4-20maDC control system
7.20 maDC
what is the demand on an analog control receiving a 8vdc from a 2-10vdc control system
75%
what is the demand on an analog control receiving a 15maDC from a 4-20madc control system
69%
