[D2L Practice] 104B

Question 1

Why are electrical thermostats preferred over electromechanical?

1) more reliable
2) auto-changeover functions
3) more accurate
4) all of the above

Answer 1

All of the above

Question 2

A furnace will operate in heat mode if the heat anticipator fails (burnt open)

Answer 2

False

Question 3

What is a high limit control used for in a residential furnace?

Answer 3

shut off gas valve if heat exchanger becomes too hot

Question 4

If the differential is set too small on a fan cut in cut out switch, what will happen to the device its controlling?

Answer 4

short cycling

Question 5

What is a fan cut in cut out switch 120F-140F used for in a residential furnace?

Answer 5

Cuts in(activate) the fan at 140F and cuts out(deactivate) the fan at 120F

Question 6

Where is the high limit switch mounted?

1) heat exchanger
2) outside
3) duct space

Answer 6

heat exchanger

Question 7

What is a manual reset on a high pressure switch?

Answer 7

If the unit trips on high pressure it will need to be physically reset

Question 8

What condensing temperature should a high pressure switch be typically set to?

Answer 8

135 F

Question 9

Cut–out(deactivate) on a low pressure control is set by?

Answer 9

cut-in minus differential

Question 10

What is the cut out if cut in is set to 80 psig with a 20 psig differential?

Answer 10

60 psig

Question 11

What does an OFC protect?

Answer 11

Compressor running without oil

Question 12

What is net oil pressure?

Answer 12

oil pump pressure minus crankcase pressure

Question 13

A control transformer can be DC.

Answer 13

False, transformers are AC