MD HVAC MASTERS ACTUAL EXAMS TEST PAPER
UPDATED QUESTIONS AND ANSWERS SURE A+
✔✔Fixed Bore Capillary tube - ✔✔Runs depending on the pressure of the condenser
outlet, doesn't control how much refrigerant flows through it, it pisses, is mostly used in
refrigerators.
✔✔Sensing Bulb - ✔✔Detects the temperature at the end of the evaporator on the
suction line and transmits this temperature, converted to pressure, to the diaphragm in
the TXV on the metering device.
✔✔Natural Draft Evaporators in Refrigerators - ✔✔Have a lot of surface area to absorb
heat, and use a manual defrost method by shutting the unit off and letting the ice melt,
most common refrigerant is R-134a
✔✔Forced/Induced Draft Evaporators in Refrigerators - ✔✔Are equipped with a fan and
are used to reduce the space the evaporator takes up, less surface area, most common
refrigerant is R-134a
✔✔Refrigerator Condensers - ✔✔Are all air-cooled can be natural or induced draft, they
are found in the back of the refrigerator, most common problem with them is lint and
dust collects which prevents air flow, most common refrigerant is R-134a
, ✔✔Wiring Diagrams - ✔✔Are either pictorial or linear that are typically shown on the
back of the refrigerator, linear is used for troubleshooting
✔✔Compressor Start Circuit in Refrigerators - ✔✔Sends power to the compressor when
it's contacts close. Is used to start the compressor by using a current magnetic relay
(CMR).
✔✔Automatic Defrost Cycle - ✔✔Is controlled by a mechanical defrost timer or
electronic timer, mechanical timers are wired so that it is energized when the
compressor is operating.
✔✔Sweat Prevention Heaters in Refrigerators - ✔✔Are small, electrically insulated
heaters that are mounted against the door openings, there function is to keep the
outside door temperature above the dew point temperature of the room so the box will
not sweat.
✔✔Refrigerant Overcharge - ✔✔Will cause a high discharge/suction pressure, sweating
will occur around suction lines, low evaporator superheat, and high subcooling
temperature,
✔✔Low Refrigerant Charge - ✔✔Will cause increased compressor run time and will run
hot, warmer box temperature, low discharge/suction pressures, high evaporator
superheat, low subcooling
✔✔Defrost in Evaporators - ✔✔Is accomplished by using heat in the discharge line of
the compressor by routing a hot gas line from the compressor discharge line to the
outlet of the metering device, and valves control flow of heat, or can be used by
electronic heaters
✔✔Frost - ✔✔Is the most common cause of inefficiency in the evaporator coils, dew will
collect on the evaporator and freeze when the coils drop below the dew point
temperature, any evaporator that runs below 32 degrees F will need a defrost cycle.
✔✔Dampers - ✔✔Located at either the inlet or outlet to the condenser, they open and
close slowly to provide a even operating system pressure.
✔✔Six Problems With Refrigeration Systems - ✔✔Low refrigerant charge, excessive
refrigerant charge, inefficient evaporator, inefficient condenser, inefficient compressor,
restriction in the refrigerant circuit
✔✔Inefficient Evaporator Symptoms - ✔✔Sweat on suction line, frost buildup, dirty coil,
fan running too slowly, flooding are starving, coil should be 35 degrees cooler than
ambient air in air conditioning and 10-20 degrees cooler in refrigeration
UPDATED QUESTIONS AND ANSWERS SURE A+
✔✔Fixed Bore Capillary tube - ✔✔Runs depending on the pressure of the condenser
outlet, doesn't control how much refrigerant flows through it, it pisses, is mostly used in
refrigerators.
✔✔Sensing Bulb - ✔✔Detects the temperature at the end of the evaporator on the
suction line and transmits this temperature, converted to pressure, to the diaphragm in
the TXV on the metering device.
✔✔Natural Draft Evaporators in Refrigerators - ✔✔Have a lot of surface area to absorb
heat, and use a manual defrost method by shutting the unit off and letting the ice melt,
most common refrigerant is R-134a
✔✔Forced/Induced Draft Evaporators in Refrigerators - ✔✔Are equipped with a fan and
are used to reduce the space the evaporator takes up, less surface area, most common
refrigerant is R-134a
✔✔Refrigerator Condensers - ✔✔Are all air-cooled can be natural or induced draft, they
are found in the back of the refrigerator, most common problem with them is lint and
dust collects which prevents air flow, most common refrigerant is R-134a
, ✔✔Wiring Diagrams - ✔✔Are either pictorial or linear that are typically shown on the
back of the refrigerator, linear is used for troubleshooting
✔✔Compressor Start Circuit in Refrigerators - ✔✔Sends power to the compressor when
it's contacts close. Is used to start the compressor by using a current magnetic relay
(CMR).
✔✔Automatic Defrost Cycle - ✔✔Is controlled by a mechanical defrost timer or
electronic timer, mechanical timers are wired so that it is energized when the
compressor is operating.
✔✔Sweat Prevention Heaters in Refrigerators - ✔✔Are small, electrically insulated
heaters that are mounted against the door openings, there function is to keep the
outside door temperature above the dew point temperature of the room so the box will
not sweat.
✔✔Refrigerant Overcharge - ✔✔Will cause a high discharge/suction pressure, sweating
will occur around suction lines, low evaporator superheat, and high subcooling
temperature,
✔✔Low Refrigerant Charge - ✔✔Will cause increased compressor run time and will run
hot, warmer box temperature, low discharge/suction pressures, high evaporator
superheat, low subcooling
✔✔Defrost in Evaporators - ✔✔Is accomplished by using heat in the discharge line of
the compressor by routing a hot gas line from the compressor discharge line to the
outlet of the metering device, and valves control flow of heat, or can be used by
electronic heaters
✔✔Frost - ✔✔Is the most common cause of inefficiency in the evaporator coils, dew will
collect on the evaporator and freeze when the coils drop below the dew point
temperature, any evaporator that runs below 32 degrees F will need a defrost cycle.
✔✔Dampers - ✔✔Located at either the inlet or outlet to the condenser, they open and
close slowly to provide a even operating system pressure.
✔✔Six Problems With Refrigeration Systems - ✔✔Low refrigerant charge, excessive
refrigerant charge, inefficient evaporator, inefficient condenser, inefficient compressor,
restriction in the refrigerant circuit
✔✔Inefficient Evaporator Symptoms - ✔✔Sweat on suction line, frost buildup, dirty coil,
fan running too slowly, flooding are starving, coil should be 35 degrees cooler than
ambient air in air conditioning and 10-20 degrees cooler in refrigeration
