UNIT 39 WITH CORRECT QUESTIONS
AND ANSWERS
A4closed-loop4system:4-4answer-Monitors4conditions4that4it4can4control.
A4control4malfunction4that4results4from4a4system4heating4or4cooling4past4its4setp
oint4is4called:4-4answer-Overshoot
A4difference4between4a4straight4heat-
cool4thermostat4and4a4heat4pump4thermostat4is4that:4-4answer-
Y4is4energized4in4both4heating4and4cooling.
A4heat4pump4condenser4contains4this4unique4control4device,4which4switches4the4f
low4of4refrigerant4depending4on4heating4or4cooling4mode.4-4answer-
Reversing4valve
A4heat4pump4defrost4control4must4do4three4things:4Turn4on4auxiliary4heat,4turn4o
ff4the4condenser4fan4motor,4and:4-4answer-
Shift4the4reversing4valve4from4heat4to4cool.
A4modulating4control:4-4answer-
Can4position4a4damper4or4valve4to4positions4other4than4full4open4or4closed.
A4switch4controls4flow4of4electricity4by:4-4answer-
Breaking4the4circuit4when4it4is4turned4off.
A4system4that4monitors4the4outdoor4temperature4to4control4some4aspect4of4syste
m4operation4is:4-4answer-An4open-loop4control4system.
A4system4that4monitors4the4return4air4temperature4to4control4room4temperature4is
:4-4answer-A4closed-loop4control4system.
An4open-loop4system:4-4answer-Monitors4conditions4that4it4cannot4control.
At4its4most4basic,4a4control4requires:4-4answer-
A4sensor,4an4actuator,4and4a4linkage.
Compared4to4electro-mechanical4controls,4pneumatic4controls4can4more4easily:4-
4answer-Provide4proportional4or4modulating4control.
Direct4digital4controls4(DDC)4operate4by:4-4answer-
Processing4electronic4signals4with4a4microprocessor.
AND ANSWERS
A4closed-loop4system:4-4answer-Monitors4conditions4that4it4can4control.
A4control4malfunction4that4results4from4a4system4heating4or4cooling4past4its4setp
oint4is4called:4-4answer-Overshoot
A4difference4between4a4straight4heat-
cool4thermostat4and4a4heat4pump4thermostat4is4that:4-4answer-
Y4is4energized4in4both4heating4and4cooling.
A4heat4pump4condenser4contains4this4unique4control4device,4which4switches4the4f
low4of4refrigerant4depending4on4heating4or4cooling4mode.4-4answer-
Reversing4valve
A4heat4pump4defrost4control4must4do4three4things:4Turn4on4auxiliary4heat,4turn4o
ff4the4condenser4fan4motor,4and:4-4answer-
Shift4the4reversing4valve4from4heat4to4cool.
A4modulating4control:4-4answer-
Can4position4a4damper4or4valve4to4positions4other4than4full4open4or4closed.
A4switch4controls4flow4of4electricity4by:4-4answer-
Breaking4the4circuit4when4it4is4turned4off.
A4system4that4monitors4the4outdoor4temperature4to4control4some4aspect4of4syste
m4operation4is:4-4answer-An4open-loop4control4system.
A4system4that4monitors4the4return4air4temperature4to4control4room4temperature4is
:4-4answer-A4closed-loop4control4system.
An4open-loop4system:4-4answer-Monitors4conditions4that4it4cannot4control.
At4its4most4basic,4a4control4requires:4-4answer-
A4sensor,4an4actuator,4and4a4linkage.
Compared4to4electro-mechanical4controls,4pneumatic4controls4can4more4easily:4-
4answer-Provide4proportional4or4modulating4control.
Direct4digital4controls4(DDC)4operate4by:4-4answer-
Processing4electronic4signals4with4a4microprocessor.