HVACR317 - Refrigeration

1. HVACR317 - Refrigeration Start Components

2. Start Components • Start components come in two types: • Capacitors • Start Relays

3. Back EMF • Whenever you spin a magnet in a coil of wires you will create voltage. • Back EMF is the excess voltage that is created in a motor. It is difficult to measure, as it is not in the same frequency as the line voltage being applied. • Back EMF produced in coils will cause the current to decrease.

4. Start Relays • The purpose of a start relay is to remove the start circuit of a single-phase compressor motor at 75% of the motor’s full rpm.

5. Start Relays • Sequence of operation: • Thermostat closes • Current goes way up – this is Locked rotor amps • Capacitor jolts start winding as it discharges. • Motor starts turning. • Creates back EMF which creates resistance and lowers amperage to FLA (Full load amps). • The back EMF which is created helps remove the start winding.

6. Start Relays • The start winding must be taken out electrically or it will burn out. • Start windings are made of thinner gauge wire than run windings, and cannot handle the excessive current. • The only purpose of a motor start winding is to get the rotor in the motor to start turning.

7. Start Relays • There are four types of start relays to learn about: • Current Relay, Coil Type • Current Relay, Hot wire type • Current Relay, Solid State type • Voltage Relay, Potential Type

8. Current Coil Relay • Current-sensitive relay that energizes on the locked rotor amps (LRA) of the motor. • Locked rotor amps are much higher than the motor’s full load amperage (FLA). • The LRA is the amperage a motor draws when it is powered, but not turning. • This is about 6 times higher than the full rating.

9. Current Coil Relay • The FLA is the amperage of the motor when it is fully operational or running at 100% of its rated rpm. • If the FLA is too high: • Condenser may be dirty. • Refrigerant may be overcharged. • Compressor may be going bad.

10. Current Coil Relay • The current coil relay will de-energize when the motor reaches its FLA rating (a second or two after the motor start). • There are two configurations of the current coil relay: • Without a start capacitor • With a start capacitor

11. R S Current Coil Relay – No Start Capacitor L2/N L1 L M S Key: L = Line M = Main (or Run) S = Start

12. R S Current Coil Relay – Start Capacitor L2/N L1 M 2 3 1 Key: 2 = Line and Start Cap 1 = Start Cap 3 = Start Winding M = Main or Run Winding sc

13. Current Coil Characteristics • Most types mount directly on the compressor motor terminals. • The relay can only be mounted right side up – gravity matters and the contacts are not spring loaded. • Look for “TOP” on the relay

14. Current Coil Characteristics • Most often used on motors that are 1 hp or less. • Has one set of normally open contacts. • The coil of the relay always gets connected in series with the run winding of the compressor.

15. Current Coil Sequence of Operation • When the thermostat closes, the LRA of the compressor will create enough magnetism through the relay to push up (close) the normally open contacts. • The coil resistance is close to 0 ohms, which allows all the voltage to be applied to the compressor run winding even though they are two loads in series.

16. Current Coil Sequence of Operation • Next, as the rotor starts to turn, back EMF starts building up in the motor windings. • The generated back EMF drops the current draw down to FLA, and the reduction in current de-energizes the relay coil. • The motor will run on the run winding only.

17. Current Coil Troubleshooting • Best method for troubleshooting is to use the ohm meter. • With the relay right side up, the coil should read 0 ohms and the contact should read infinity. • With the relay upside down, the coil should be 0 ohms and the contact should read 0 ohms. • When finding a replacement part, use the model number of the compressor.

18. Current Coil Troubleshooting • The most common symptom of a bad relay is a hum/click sort of noise. The first time you hear it, you will know it.

19. Hot Wire Relay • Older design very seldom used anymore. • Replaced by the current coil or solid state type. • Also used on fractional horsepower motors (less than 1 hp)

20. R S Hot Wire Diagram L2/N M L1 L S Key: L = Line S = Start Winding M = Main or Run Winding

21. Hot Wire Relay Characteristics • Contains two sets of normally closed contacts. • Operates thermally by current flow that creates heat through a small wire. • The heat will warp a bi-metal contact (the S) which opens it. • Breaks path to start winding.

22. Hot Wire Relay Characteristics • The relay has its own overload protection. • If the motor gets stuck in LRA the second contact (M) will heat up and open as well. • Does not need a motor overload switch.

23. Hot Wire Relay Troubleshooting • Any problems with starting? Replace it with a solid state relay.

24. Current Relay – Solid State • Solid State means it is a non-mechanical device (no moving parts). • This relay is also known as a thermistor type relay or a PTC relay. • A Thermistor is a device that changes its resistance value as current passes through it.

25. Thermistor Diagram

26. Solid State Relay • PTC stands for Positive Temperature Co-efficient. The higher the temperature of the device, the less efficiently current can pass through the device. • Solid state relays are also used mostly on fractional (under 1 hp) motors.

27. Solid State Relay - PTC

28. Solid State Relay Characteristics • The relay is made of a conductive ceramic. • The ceramic disk is about the size of a dime and has a very low resistance (about 3 to 5 ohms) when at room temperature. • When the current passes through the disk, the resistance rapidly increases to a value of about 80K ohms.

29. Solid State Relay Diagram R 3-5 Ohm Rating C S

30. Solid State Sequence of Operations • The thermostat closes • The motor achieves LRA. • The current heats the relay. • At about 80K ohm of resistance, the start winding is effectively removed from the circuit, with all power flowing through the run winding.

31. Types of Solid State Relays • There are three types of solid state relays: • Plug in type • Two wire type • Five wire type

32. R N C S Plug-in Diagram

33. R N C S Two Wire Diagram Thermistor is wired in series with start winding

34. Five Wire Diagram S C S L L R R C N

35. Solid State Relays • The two and the five wire types are field replacement types. They can be used to replace the plug-in, the current coil, and the hot wire. • Make sure you check hp (horsepower) ratings before using replacement.

36. Solid State Relay Troubleshooting • The best method to use for troubleshooting is an ohm meter. • When at room temperature, look for three to five ohms. • If the solid state relay is warm, look for a high resistance.

37. Potential Relay • An electromagnetic type relay. • Uses voltage to operate in the same principle as a control relay. • Potential relays ALWAYS use a start capacitor. • Most of the time there will also be a run capacitor.

38. Potential Relay A Potential relay, a run capacitor and a start capacitor.

39. 2 5 1 Potential Relay Schematic

40. Potential Relay Characteristics • Contains one set of normally closed contacts. • Coil has a resistance of 6000 to 12000 ohms. • Between pins 1 and 5 you should have 6-12K ohms. • Between pins 1 and 2 you should have 0 ohms. • The coil voltage is generated by the back EMF across the compressor start winding.

41. Potential Relay Characteristics • It is used on compressor motors from ½ to 10 hp. • Potential relays and start capacitors provide a very high starting torque. • Anything that needs power beyond this point will require a three-phase compressor.

42. 2 5 1 Potential Relay Wiring Terminal 1  Start Capacitor Terminal 2  Connects to start winding Terminal 3  Connects to compressor common, or motor overload Sometimes the relay will come equipped with a terminal 3, 4, and 6 – these are dummy terminals used for junction points only.

43. R 2 5 1 N C S Potential with only start cap L1 SC

44. R 2 5 1 N C S Potential with start and run capacitor L1 RC SC

45. Potential Relay Troubleshooting • Use an ohm meter to detect problems. • Test the contacts between 1 and 2; this should be a 0 ohm reading. • Test the coil between 2 and 5; this should be a very high resistance. • Complete test 1 to 5; should be a very high resistance as the coil and the contacts are getting checked together.

46. General Troubleshooting • Sometimes on very high microfarad capacitors, there is a bleed resistor across the terminals. This is designed to purge voltage out of the capacitor. Do not trust it - always bleed the capacitor yourself. • If the start winding is open the Motor Overload will trip.

47. General Troubleshooting • If the run winding is open the motor will not start, but the overload (MOL) will not trip.

48. Hard Start Kits • A hard-start kit is a combination of a start capacitor and relay. • Refrigeration hard-start kits contain a solid state relay and do not have a microfarad (mfd) rating. They cannot exceed ½ hp. • Air conditioning hard-start kits contain a potential relay and can range from ½ to 5 horsepower.