HVACR214 – Oil Electrical

1. HVACR214 – Oil Electrical Relays and Contactors

2. Relays • The relay is an electrical device consisting of a coil and a set of contacts. • The coil and the contacts are isolated (protected) from each other. • It is designed to be useable where one circuit must control another.

3. The relay coil • A coil is a spool of wire that is wrapped around an iron core. When the wire is energized (electricity is applied to it) there is a magnetic field generated. • This field pulls in an armature that closes or opens a set of contacts. • When a relay is shown in a schematic it is always shown in the de-energized mode.

4. The relay coil • Every coil has a voltage rating. This rating is the voltage that you may apply to the coil. • These ratings are normally 24 volt, 120 volt, 208/230 volt. • You may not apply 120 volts to a 24 volt coil and you may not apply 24 volts to a 120 volt coil.

5. The relay coil • The coils rating is normally stamped on the side of the relay. • The coil is a load in a schematic circuit.

6. The contacts • Relay contacts are the switching device of the relay. • When contacts are in a schematic they are treated as an open of closed switch. • Relay contacts come in two varieties. • Normally Open • Normally Closed

7. Relay contacts • Relay contacts are attached to the armature that is moved by the magnetic force of the coil. • Relay contacts have metal points that come in contact with each other. These points complete the circuit.

8. Normally Open Contacts • Normally open contacts are the equivalent of an open switch. • When the relay coil is de-energized it is an open in the circuit. • When the relay coil is energized they close, just like turning on a light switch. • When the coil is de-energized again they open.

9. Normally closed contacts • A normally closed contact is a closed switch when the coil is de-energized. • When the coil is energized the switch opens and stops current from reaching the load. • When the coil is de-energized again the contacts close.

10. Contact ratings • The contacts are rated with the number of amps they can control. • The contacts are also rated with the type of load they can control. This would either be “inductive” like a motor, or “resistive” like a heater.

11. Contact ratings • With inductive loads the amperage spikes when it is starting. • With resistive loads the amperage remains constant. • Make sure the contact ratings exceed the maximum amperage that the load is rated for.

12. Sequence of operation • Every component has a sequence of operation. • A good technician can always describe the operation of the circuit to someone over the phone by giving a sequence of operation.

13. Sequence of a MARS relay • When the relay is de-energized there is no power across the coil • The contacts between points 1 and 3 are normally open. • The contacts between points 1 and 2 are normally closed. • The relay coil is energized with 24 volts. This closes the contacts between 1 and 3 and opens the contact between 1 and 2.

14. Schematic Symbols of a relay Relay Coil Normally Open Contact Normally Closed Contact

15. Relays • Again, a relay is designed to control loads in the same circuit or another circuit.

16. Relays - Example 1 120 V N L1 C1 C1 C1 SW1

17. Relays - Example 1 • In example 1 • The switch SW1 is open and coil C1 is not energized. Thus the normally open contact C1 is open and the green load is not energized. The normally closed contact C1 is closed and the red load is energized.

18. Relays - Example 2 120 V N L1 C1 C1 C1 SW1

19. Relays - Example 2 • In example 2 the switch SW1 has been closed. This has energized the relay coil C1. When the coil was energized the normally closed contact C1 was opened and de-energized the red bulb. The normally open contact C1 was closed and this energized the green bulb.

20. MARS Relay The MARS relay is one of the most frequent relays you will see. It consists of a coil and 2 sets of isolated contacts. Each set has a common, normally open and normally closed contact.

21. MARS Relay Normally Open Normally Closed Coil Common

22. MARS Relay - Normally Open

23. MARS Relay - Normally Closed

24. Mars Relay - Schematic 4 1 3 2 6 5

25. Contactors • Contactors are really close in operation to relays. • Contactors have one or two sets of contacts that are normally open. • Contactors are designed to be switching devices for loads with high amperages. • Most contactors use control voltage (low) voltage to control high voltage loads.

26. Contactors • Contactor coils are rated by voltage. • Contactor contacts are rated by amperage. • These ratings are normally written on the side of the contactor. • Do not install a contactor that goes over either of these ratings.

27. Contactor

28. Contactor

29. Contactor - Schematic

30. Troubleshooting contactors and relays • Troubleshooting contactors and relays is a matter of looking at voltages across loads and switches. In the following example B2 is not working when SW1 is turned on.

31. Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1

32. 120V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 First make sure circuit has power across L1 and N

33. Troubleshooting contactors and relays 0 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Close switch and check from L to line of SW1

34. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to load of SW1

35. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to line of C1

36. Troubleshooting contactors and relays 120 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to neutral of C1

37. Troubleshooting contactors and relays 120 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to neutral of C1 at end of branch

38. Troubleshooting contactors and relays 0 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to line of C1 contact

39. Troubleshooting contactors and relays 0 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to load of C1 contact

40. Troubleshooting contactors and relays 0 V N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to line of C2 coil

41. 120 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to neutral of C2 coil

42. 120 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to neutral of C2 coil at end of branch

43. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to line of C2 contact

44. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to load of C2 contact

45. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to lline of B2 load

46. 0 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to load of C2 contact

47. 120 V Troubleshooting contactors and relays N C2 C2 L B2 C1 B1 C2 C1 C1 SW1 Next - Check from L to neutral of C2 contact

48. Troubleshooting contactors and relays • Based on the last 2 measurements the technician would determine that contactor C2 has a bad contact. • The voltage across a load should NOT be 0. • The voltage across a closed switch or contact should NOT be source.

49. Review • A relay and and a contactor is an electro-mechanical device used by one circuit to control another. • The voltage is the Coil voltage. • The Amperage is how the contacts are rated. • It can control two separate voltages in one or two circuits.