HVAC Compressors and Condensing Units 3

Question 1

What is the difference between a semi-hermetic and a fully hermetic compressor?

Accepted Answer

Semi-hermetic compressors have bolted serviceable housings while fully hermetic compressors are welded shut

Answer

Semi-hermetic compressors are smaller and used only in residential equipment

Answer

Semi-hermetic compressors use a belt drive while fully hermetic units are direct drive

Answer

Semi-hermetic compressors do not use oil lubrication

Question 2

What is the typical cause of high head pressure on an air-cooled condensing unit?

Accepted Answer

Dirty or blocked condenser coil restricting airflow

Answer

Low refrigerant charge

Answer

Worn compressor valve reeds

Answer

Low ambient temperature during operation

Question 3

What does low suction pressure typically indicate in a refrigeration system?

Accepted Answer

Restricted metering device or low refrigerant charge

Answer

Overcharge of refrigerant

Answer

Condenser fan motor failure

Answer

High ambient temperature conditions

Question 4

Which condition can cause a compressor to draw excessive amperage (high amps)?

Accepted Answer

High suction and discharge pressures due to an overcharge or condenser issue

Answer

Low refrigerant charge

Answer

Clean air filters with unrestricted airflow

Answer

Low ambient outdoor temperature

Question 5

What is 'oil logging' in an evaporator coil?

Accepted Answer

Refrigerant oil accumulating in the evaporator coil and reducing heat transfer

Answer

Excessive lubrication applied to the evaporator fan bearings

Answer

Oil contaminating the refrigerant charge from a factory defect

Answer

Oil leaking from the compressor onto the condenser coil

Question 6

What is the purpose of a reversing valve in a heat pump condensing unit?

Accepted Answer

Reverse the direction of refrigerant flow to switch between heating and cooling modes

Answer

Control compressor speed during partial-load operation

Answer

Bypass the compressor during defrost cycles

Answer

Regulate the flow of refrigerant to multiple evaporator zones

Question 7

When replacing a compressor, why is it important to flush the refrigerant circuit?

Accepted Answer

To remove acid, carbon, and metallic debris left by a burned-out compressor

Answer

To remove moisture that accumulated during the compressor failure

Answer

To recharge the system with the correct refrigerant oil type

Answer

To test the reversing valve for proper operation