Course: HET 119 HVACR Electricity II

Lab Assignment

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Week 12 Lab Assignment: Refrigeration Control Devices

Recommended Materials
1. Lab Sheet
2. Pencil and paper
3. HVAC Textbook
4. Internet Search
5. Test Board 24”x 24”
6. Wires
7. Refrigeration Thermostat
8. Defrost Thermostat
9. Defrost Termination
10. Defrost Timer (8145-00)
11. Low Pressure Control (optional)
12. High Pressure Control (optional)
13. Contactor (optional)
14. 3 Light bulbs and fixtures (The lights will be used for the Defrost Heater, compressor, condenser fan motor, and evaporator fan motor)
15. Jumper wires

Scope

This lab will help the student to understand Control Devices and how it is used in electrical circuits in refrigeration systems. The student will wire controls to loads in combination circuits.

Procedures

1. Follow the diagram posted, use light bulb as the loads.
2. On a test board, wire a circuit as an air conditioning system.
3. Have the instructor specify the controls you will need for this assignment.
4. Have the instructor to inspect the circuit.
5. Cycle the Defrost Timer to witness the operation of the compressor and the defrost heater.
6. Cycle the thermostat and witness the action of the loads.
7. Use a jumper wire to bypass the pressure controls if used.
8. Witness the operation of the loads of the pressure controls.
9. Witness the action from the thermostat.
10. Explain what is the purpose of these controls:
  1. Compressor
  2. Condenser Fan Motor
  3. Liquid Line Solenoid
  4. Low Pressure Control
  5. Refrigeration Thermostat
  6. Contactor
  7. Defrost Heater
  8. Defrost Timer
  9. Defrost Termination Thermostat
  10. Fan Delay Switch
  11. Defrost Heater Limit Switch

Research Questions

1. Explain the sequence of the defrost system.
2. How often does the defrost clock operate?  Why?
3. In this schematic, what is the purpose of the Defrost Thermostat?
4. What cycles the Evaporator Fan Motor off?

Click on the file below to download the Lab Assignment
- HET 119 Wk 12 Lab.docx (54.11 KB)