Electrical Operating Sequence
The power circuit is the first to be examined, because power must be available to operate the loads.
For a refrigeration system with an air-cooled condenser, the three principal loads that must be energized are:
1- The compressor motor
2- The condenser fan motor
3- The evaporator fan motor
The technician must be certain that the proper voltage is being supplied to the loads.
1- The supply-line voltage should be tested with a voltmeter and then compared to the manufacturer’s recommended values.
2- If the voltage is correct, then the circuit will need to be tested further.
Before energizing the circuit, always use your meter to check for ground faults.
Once energized, the voltage for each load in the circuit can be tested.
A clamp-on ammeter can be used to check the current draw for each load one at a time.
The measured current should be compared to the current rating listed on the motor nameplate.
Electrical Operating Sequence
In troubleshooting, when a load is not working, the technician must determine whether the problem is in the load itself or in the switches that control the load.
If the proper supply voltage is available but the compressor or fan motor does not run, then there may be a fault in the control circuit and the control circuit voltage should be tested.
Generally, the control circuit voltage will be much lower than the line voltage.
Always test to determine if the fan or motor is tripped on a safety switch before replacing components.
When checking components with an ohmmeter, it is important that all power is disconnected and the component part is electrically isolated.
Short circuits are usually due to faulty loads.
Wiring Diagrams
Wiring diagrams usually consist of:
Connection diagrams:
Show the wires to the various electrical component terminals in their approximate location on the unit
This is the diagram that the technician must use to locate the test points.
Schematic diagrams:
Separate each circuit to clearly indicate the function of switches that control each load
This is the diagram the technician uses to determine the sequence of operation for the system.
Diagnostic Tests
Diagnostic tests can be conducted on electronic circuit boards, conducted at points indicated by the manufacturer, or used to check voltages or other essential information critical to the operation of the unit.
Some electronically controlled systems have automatic testing features, which indicate by code number a malfunction in the operation of the equipment.
Further tests are usually required to determine the action that is required.
Troubleshooting Tables
Troubleshooting tables are helpful as a guide to corrective action.
By a process of elimination, such tables offer a quick way to solve a service problem.
The process of elimination permits the technician to examine each suggested remedy and disregard ones that do not apply or are impractical.
Split-System Mechanical Problems
The problems associated with a system that starts and runs but does not produce satisfactory cooling can be divided into two categories: refrigerant quantity or refrigerant flow rate.
To determine the problem, use the information listed in this table for measurements. These results, when compared to normal operating results, will generally identify the problem.
DX Coil Operating Temperature
Normal coil operating temperatures can be found by subtracting the design DX coil split from the average air temperature going through the coil.
The DX coil split will vary with the system design.
The term coil split is also often referred to as the temperature split or the approach temperature.
This is the difference in temperature between the coil (condenser or evaporator) and the air passing across it.
The energy efficiency ratio (EER) is the output in BTU/hr divided by the power input measured in watts.
The EER is useful in determining coil-operating temperatures.
7.0 to 8.0 EER: DX coil design splits in the range of 25°F to 30°F
8.0 to 9.0 EER: DX coil design splits in the range of 20°F to 25°F
9.0+ EER: DX coil design splits in the range of 15°F to 20°F