1. E2 Motors and Motor Starting
#2 Compressor Relays and Capacitors

2. Single Phase Compressor Starting
Single phase compressors have a start winding and a run winding
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

3. Split Phase Compressor Motor
RUN WINDING
START WINDING
COM
V/  V AC DC S Ω Ω Ω R
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

4. Starting a Split Phase Compressor
Power must first go to both the run winding and the start winding
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5. Split-Phase Compressor Motor Starting
Power is also needed to start C R
START WINDING
RUN WINDING
A split phase motor is the basic design for motors used in all HVACR applications.
The run winding uses heavy wire, while the finer wire of the start winding provides the resistance and phase shift necessary to start the motor.
Once the motor is started we need to take the start winding out of the circuit.
We can accomplish this with either a current relay or a potential relay.
Once started, the start windings are removed from the circuit
Power is needed for the motor to run
LINE
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

6. Start Relays A relay is used to energize the start winding
The same relay is also used to take the start winding out of the circuit
The next slide is a diagram of where start components are located in a compressor motor circuit
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

7. Diagram of Compressor Start Components
For the motor to run, power is needed to Common and Run N L1 C S R
For the motor to start, power is needed to the Start terminal.
Add torque with a Start Capacitor
After start up, A Start Relay opens the circuit
START
RELAY
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

8. Types of Compressor Starting
RSIR: Resistance start, induction run
Uses a start relay only
CSIR: Capacitor start, induction run
Uses a start relay and start capacitor
CSCR: Capacitor start, capacitor run
Uses a start relay and both start and run capacitors
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

9. Two Types of Starting Relays
Current Relays
Potential Relays
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10. Current and Potential Relay
Two types of relays used are current and potential relays.
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11. Current Relays Used on compressors under one horsepower
Switch contacts are normally open (NO)
Relay coil energized by high starting current
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12. Current Relay
The current relay is generally limited to motors used in welded compressors through 3/4 hp and semi-hermetic through 1/4 hp. It senses current in the main or run winding and its contacts are normally open.
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

13. Motor Amp Draw on Start up
Current relays respond to amp draw
Relay contacts close on high starting current
Relay contacts open as amperage drops
Motors draw high amps (LRA) on start up.
LRA
60A
40A
20A 0A
Amperage drops as speed increases.
Amperage Draw
Start Up
RLA
20% 40% 60% 80% 100%
Motor Speed
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

14. Starting with a Current Relay
Current relays are used on refrigeration systems with fixed metering devices
When system pressures are equalized only a relay is needed to start the compressor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

15. Split Phase Motor with Current Relay
1- High starting amps energize relay coil, close contacts
2- Line voltage goes to start windings
3- Motor speed increases, amperage decreases, relay coil allows contacts to open C R S
START WINDING
RUN WINDING S M
4- Start Winding drops out
CURRENT RELAY
This split phase motor above uses a current relay to take the start winding out of the circuit. Since the starting torque is low this type of motor is used in fractional HP compressors on cap tube systems.
When a motor starts, its momentary starting current is about 5 times its normal running current.
As the coil of the relay senses the tremendous inrush of starting current it closes the normally open contacts. This allows power to go to the start winding which starts the motor turning.
The motor reaches its operating speed within 2 seconds.
At this point the current relay coil senses a reduction in current from its starting current to its running current. This drops out the relay, opening the relay contacts and cutting power to the start winding.
The motor continues to operate on the run windings until power is interrupted to the motor.
5- Motor continues to run,
drawing normal current L
POWER ON
Original Diagram from Copeland Handbook
LINE
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

16. How a Current Relay Works
The drawing on the next slide shows how the start winding is energized, then how it is taken out of the circuit
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

17. Current Relay 1 2 S M Jumper wire
Also used to connect optional start capacitor
Power In 1 2 S M
To Start Terminal
Relay Coil
To Main (Run) Terminal
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

18. Energize Start and Run Windings
Voltage ready for Start Winding
Contacts close
Voltage through coil
Power to Start Winding
High starting current increases coil magnetism
Power to Main (RUN) Winding
Plunger is pulled up
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

19. Start winding de-energized
No voltage to Start Winding
Plate falls, contacts open
Power to Start Winding
As motor speed increases, amperage falls
Power to Main (RUN) Winding
Plunger falls
Compressor continues running
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

20. Adding a Start Capacitor
A refrigeration system with a TEV requires more starting torque
Adding a start capacitor in series with the start winding is all that is needed
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

21. Capacitor Start Induction Run Motor (CSIR)
START WINDING
RUN WINDING S M
CURRENT RELAY
This capacitor start, induction run (CSIR) motor is using a current relay and everything is the same as the previous example of a split phase motor.
Except, we have added a start capacitor in the line to the start winding.
The start capacitor gives greater starting torque to the motor. These are usually required on TEV systems because the compressor may have to start before the system pressures have equalized.
The capacitor will only be energized while the relay contacts are closed. L
LINE
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

22. Start Capacitors They provide more phase shift to the start winding
Start capacitors are designed to be in the circuit for only a few seconds
A resistor quickly bleeds off capacitor charge to prevent excessive arcing across the relay contacts
Note: Always replace capacitors with the same microfarad rating (MFD or µF) and equal (or greater) volt amp capacity (VAC)
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

23. Start Capacitor Bleed Resistor 15,000 Ohms
Here is a view of a start capacitor. Note the use of a bleed resistor which bleeds the capacitor down in a few seconds when the circuit is opened. This is a must to prevent burned relay contacts. It is a 15,000 to 18,000 Ohm 2 watt resistor.
Bleed Resistor 15,000 Ohms
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

24. Terminal box on a small compressor
A current relay plugs into the start and run terminals
The external overload is mounted inside the terminal box
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25. Current Relay and Overload
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26. Current Relay and OverloadS
Current Relay and Overload
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27. Terminals - Current Relays - Overloads
Jumper Wire   S R L1 N
Remove jumper wire when installing start capacitor
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28. Two-wire Overload
Single phase overloads are usually in the common wire
Its bimetal disk warps when heated
It responds to motor heat and amperage
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

29. 2-wire bimetal overload3
Power on
Load 1 2
Normal operating condition: 1-2 closed
If the load draws high current, the heater from 2-3 becomes hot
This warps bimetal 1-2, and
opens the circuit between 2 and the Load
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

30. Potential Relays
Used for starting single phase compressors up to five horsepower
Contacts are normally closed (NC)
The relay coil is energized by Back EMF (electromotive force) generated in the start winding
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

31. Potential Relay – Top ViewS
“Dummy” terminal 2
To start terminal
From common terminal
Contacts
Solenoid Coil
“Dummy” terminal C 1 5 R
From run terminal
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32. Potential Relay Exposed2 1 5
Normally Closed (NC) contacts between terminals 1 and 2
Relay Coil
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33. Potential Relay – Normal Position
Normally closed contacts
Relay Coil
De-energized
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34. Potential Relay – After Start Up
Contacts 1 to 2 are pulled open
Relay Coil
energized
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

35. Potential Relays in Operation
The normally closed contacts allow full voltage to the start winding
The relay coil is energized
The contacts open
Back EMF keeps the coil energized, which keeps the contacts open
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

36. Potential Relay Capacitor Start Induction Run (CSIR) Motor2 1
START
CAPACITOR
POTENTIAL RELAY
Back EMF keeps the coil energized 5 C R S
START WINDING
RUN WINDING
Larger split phase motors require a potential relay with a capacitor.
When power is supplied to the common it supplies power to one side of the potential relay coil at terminal 5.
Power from the R terminal goes through the start capacitor, through the normally closed contacts of the relay, and to the S terminal on the start winding.
When the motor starts it creates a high voltage that energizes the relay coil, opening the contacts 1 & 2 of the relay. This disconnects the start winding from the circuit.
The run windings generate enough voltage (or back EMF) to keep the contacts open as long as the motor is running at it’s normal speed.
The potential relay senses voltage. Actually, it reacts to 3 voltages:
The “pick up” voltage is back EMF (electro magnetic field) voltage generated across the start winding by the motor’s rotor when it is up to about ¾ speed. This pulls the contacts open between terminals 1 and 2. This takes both the start capacitor and start windings out of the circuit.
The “drop out” voltage is the back EMF voltage that must be generated across the relay coil to “hold” the contacts 1 and 2 open once they have been picked up.
3.The “continuous” voltage is the maximum back EMF that the relay’s coil can tolerate continuously without overheating and opening the circuit.
When replacing a potential relay make sure these voltages are the same on the new relay.
LINE
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

37. Adding a Run Capacitor
A run capacitor is added to the starting circuit
When the potential relay opens the run cap stays in the circuit
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

38. Potential Relay Capacitor Start-Capacitor Run (CSCR) Motor
RUN CAPACITOR 2 1
START
CAPACITOR
POTENTIAL RELAY
Back EMF keeps the coil energized 5 C S R
START WINDING
RUN WINDING
This is basically the same as the previous CSIR motor using a potential relay and capacitor, except there has been a run capacitor added parallel with the start cap. The motor is stronger because the start winding is now carrying part of the running load after the start cap has been disconnected.
The use of a run cap also improves the power factor, reduces motor current, increases efficiency, and decreases motor temperature. However, it is not just a matter of adding a run cap to a CSIR motor. The CSCR motor has been specially designed for this type of use.
If the run capacitor fails it the motor will start, but it will draw about 10% more amps than it should. Under full load conditions it may draw even higher amps, causing it to go out on overload.
Potential relays are used with the CSCR motors because the failure of a current relay is more likely when a run capacitor is used.
Capacitor start-capacitor run motors have high efficiency, high starting torque, and high power factor. They are used in compressors up to 5 HP.
The run capacitor stays in the circuit for greater motor efficiency
LINE
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

39. Run Capacitors
When the compressor is running, a run capacitor provides partial voltage to the start winding
This lowers compressor amperage, increasing motor efficiency
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

40. Run Capacitors Old style New Style
A run capacitor is designed to stay in the circuit all the time. It is larger in size and packaged in a metal can. It should be noted that if the run capacitor has polarity, the terminal that is marked should always be wired to the ‘r’ terminal of the motor. This keeps a grounded capacitor from burning out the start winding. The new style capacitor is made from a material which will burn itself free of a grounded condition.
Old style
New Style
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

41. Run Capacitors on PSC Compressors
No start relay is used on PSC motors
A run capacitor is permanently wired into the start windings
PSC compressors are used on fixed metering device air conditioning systems, where pressures equalize during the off cycle
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

42. Permanent Split Capacitor (PSC) Compressor
Run Capacitor
Run Cap allows partial voltage to start winding S C R
Start Winding
Run Winding
A permanent split capacitor motor is used for applications which do not require high starting torque. It is simply a split phase motor with a run capacitor installed between the R and S terminals. There is no start relay!
This motor is economical and efficient. A PSC motor is limited to systems whose pressures are equalized prior to start up, usually A/C systems with fixed metering device (nozzle, cap tube, etc.).
It is used mainly for blower motors and condenser fan motors.
Line
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

43. PSC* Compressor with Run Capacitor
starts and runs
efficiently
LINE S C R C S R
Energize start
winding
Partial voltage
through run cap
Power is applied to the the compressor at terminals C and R.
From R, power goes to the run capacitor but passes full voltage through the PTC (positive temperature coefficient) relay, effectively bypassing the run capacitor.
When the compressor has started, the PTC relay is so hot that there is too much resistance for power to flow through it.
This forces the voltage through the run capacitor which provides a phase shift to the running compressor that keeps it running cool and efficiently.
Run Capacitor
Compressor
*Permanent Split Capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

44. PTC Relays Positive Temperature Coefficient (PTC) solid state relays
The resistance of the ceramic disc increases with temperature
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45. P.T.C. Relay Cutaway Wire spring holds disk and serves as a conductor
Start
Run
Power from Run terminal
Power to Start terminal
Ceramic Disk
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

46. Location of the PTC Relay
The relay is wired in parallel to the run capacitor
It allows full voltage starting, then drops out of the circuit
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

47. PTC Relay and Run Capacitor
Relay is wired in parallel with the run capacitor
A recent development of solid state technology has made a different type of current sensitive relay available, the positive temperature coefficient or PTC starting switch. Certain solid state materials have the unique property of increasing their resistance as they sense current.
Placed in series with the start winding, the device normally has low resistance. Upon start-up, the resistance raises rapidly and to a high enough value to reduce the start winding current to a trickle. This effectively takes the start winding out of the circuit.
Because it takes several minutes (3-10) to cool down, it is not feasible for applications requiring shorter cycle times.
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

48. PTC Relay in Operation
When cool, the disk allows full voltage to the start winding
The disk heats up quickly, stopping the flow of voltage
Power then takes the path of least resistance through the run cap to the start terminal
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

49. Start Assist with PTC* Relay
Voltage stops
when relay heats
LINE
Starts with
full voltage
to start winding S C R C S S R
Runs with
partial voltage
through run cap
Power is applied to the the compressor at terminals C and R.
From R, power goes to the run capacitor but passes full voltage through the PTC (positive temperature coefficient) relay, effectively bypassing the run capacitor.
When the compressor has started, the PTC relay is so hot that there is too much resistance for power to flow through it.
This forces the voltage through the run capacitor which provides a phase shift to the running compressor that keeps it running cool and efficiently.
Run Capacitor
Compressor
*Positive Temperature Coefficient
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

50. “Hard Start” Kits
Used on air conditioning compressors when compressor has trouble starting
Contains a solid state relay and start capacitor
Installed parallel to the run capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

51. Hard Start Kit (for PSC Compressor)
PTC Relay
Connect Leads to both sides of the RUN Capacitor
Start Capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

52. Power to Hard Start Kit Start Capacitor PTC Relay
Full power plus start capacitor to start winding
Incoming power on start up
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53. Hard Start Kit Out of the Circuit
PTC Relay
Start Capacitor
PTC Relay heats up
Current flow stops
Incoming power now goes through RUN cap
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

54. Hard Start Kit Added to PSC Compressor
The following slide shows the start kit in the starting circuit
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55. PSC Compressor Start Assist
Hard Start Kit
(PTCR & Start Cap)
Full Power plus
Start cap to Start
PTCR heats up,
Stops current flow
LINE S C R C S S R
Power is applied to the the compressor at terminals C and R.
From R, power goes to the run capacitor but passes full voltage through the PTC (positive temperature coefficient) relay, effectively bypassing the run capacitor.
When the compressor has started, the PTC relay is so hot that there is too much resistance for power to flow through it.
This forces the voltage through the run capacitor which provides a phase shift to the running compressor that keeps it running cool and efficiently.
Current now
goes through
only the run cap.
PSC Compressor
Run Capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

56. Solid State Potential Relays
Use only if the OEM (Original Equipment Manufacturer) potential relay is not available
Use only as a temporary replacement of OEM potential relay
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

57. Electronic potential relay start kits
Hard Start Kit
Replacement Relays
Replacement Relays
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

58. Diagram of SS Potential Relay
OEM potential relay coils operate on Back EMF
Solid state potential relay coils operate on time to open the start circuit
The wiring hookup is basically the same as the original relay
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

59. Electronic Start Relays (Universal replacement relay PRO-90 by SUPCO)
Run
Cap L1 N
O.L. R S C
Run Cap acts like a jumper wire 2 5
Timer opens 1-2 1 4 6
Start
Cap
Run cap provides efficient running
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

60. Solid State Current Relay Kits
Useful on small hermetic refrigeration compressors
Replaces the current relay and capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

61. Start Kit for Small Refrigeration Units
PTC Relay
Incoming Power
Start Capacitor
To START terminal
To RUN terminal
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

62. Installing a Start Kit
The following slide shows how the start kit is hooked up to the compressor
Use the original overload, NEVER jump out the overload
Note: This kit can be used even if the original compressor did not have a start capacitor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

63. Replacing a Start Relay with a Start Kit
Connect L1 & Run
Remove Relay L1 L1
PTC Relay
&
Start Capacitor N
Connect to Start
Use existing overload
Start Compressor
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

64. Start Kit with Overload
Some kits include an overload
This kit can replace all the starting components at one time
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

65. Electronic current relay start kit
Power Leads
Terminal connections for Run, Start, & Common
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2

66. Inside a “3 in 1” Kit Start Capacitor N L1 C S R PTCR PTCR OVERLOAD
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67. END OF Compressor Relays and Capacitors
© 2005 Refrigeration Training Services - E2#2 Compressor Relays and Capacitors v1.2