[D2L] 104D HVAC Control Circuits

Question 1

Continuous control mode provides among the highest levels of human comfort available

T or F

Answer 1

True

Question 2

A controller has a range of 50F-86F, but is set to 64F-73F. Which is the control range and which is the actual operating range?

Answer 2

50F - 86F is the control range
64F - 73F is the actual range

Question 3

Where is a zone thermostat typically located?

Answer 3

Inside the space it is controlling

Question 4

A low ambient limit thermostat energizes the compressor if the outside ambient temperature drops below 50F

Answer 4

False, it will be de-energized

Question 5

What temperature do low ambient limit thermostats cut out at?

Answer 5

50F

Cut in - activates the compressor (ex. if temp rises to 40F)
Cut out - deactivates the compressor (ex. if temp drops to 35F)

Question 6

What is the difference between mechanical cooling and free cooling?

Answer 6

Mechanical cooling operates the compressor
Free cooling opens up the fresh air damper

Question 7

What thermostat is used to prevent the compressor from starting if the evaporator is too cold?

1) close on drop of temperature switch
2) open on rise of temperature switch
3) close on rise of temperature switch
4) open on drop of temperature switch

Answer 7

open on drop of temperature switch

Question 8

What will happen to an evaporator running below 32°F?

Answer 8

condensate collects on the evaporator and quickly restricts airflow

Question 9

If your high limit has failed, it is acceptable to place a jumper across it.

Answer 9

False

Question 10

What is usually the non-adjustable set point for a high limit thermostat?

Answer 10

180F-220F

Question 11

What is a roll out limit thermostat used for?

Answer 11

interrupt the heating cycle during a primary burner malfunction

Question 12

What is a spill limit thermostat used for?

Answer 12

Located on a flue hood in case of a back draft problem

Question 13

What can cause a back draft problem?

1) negative building static pressure
2) plugged flue vent
3) incorrectly sized flue vent
4) plugged combustion air intake
5) all of the above

Answer 13

All of the above

Question 14

In order to prevent a residential furnace blowing cold air, a fan control thermostat is wired to ensure the heat exchanger temperature is warm enough before starting the fan

T or F

Answer 14

True

Question 15

What is a combustion air proving switch used for?

Answer 15

ensure sufficient air volume moves through a gas-fired appliance before igniting

Question 16

A centrifugal Switch closes when a motor has stopped rotating

Answer 16

False

Question 17

Economizers contain 2 external sensors which are (MULTI-SELECT)

1) Indoor air sensor
2) Outdoor air sensor
3) Mixed air sensor
4) combustion air sensor

Answer 17

Outdoor air sensor
Mixed air sensor

Question 18

Most common supply voltage for a Zone Thermostat?

Answer 18

24vAC

Question 19

An Overload Device protects the Load

Answer 19

True