1. Air Conditioning
Starting Relays

4. Starting Relays
Purpose
Remove the start winding and/or start capacitor from the circuit
Compressor start relays are mounted outside the motor
Centrifugal switch could not be used in hermetic motor

5. These are the three most common
Types of Relays
These are the three most common
The HP of the motor will determine what type will be used
Service man may replace not re-design.

6. Three types Current Coil Relay Solid State Relay or PTC
Potential Relay

7. Current Coil Relay Works off amperage to the run winding.
On compressor start up:
Motor draws high current
Induces a strong magnetic field in the relay’s magnetic coil through the run winding
This magnetic field lifts a plunger with
contacts and a counter tension spring
Contacts to start winding are made
Start winding is energized

11. Motor now starts because start winding
creates a strong magnetic field
Motor reaches 75% running capability:
Current drops down
Relay coil is in series with run winding
Not enough current remains to keep coil magnetized
Spring pushes plunger down
START WINDING IS DE-ENERGIZED

12. Used mainly on fractional horsepower compressors for small refrigeration units, not A/C

15. Solid State Relay Also works off current
Has materials that changes its resistance
PTC-Positive Temperature Coefficient
Temp goes up/ resistance goes up
Wired in series with start winding only

16. Uses up voltage (loads in series)
Example:
Voltage drop across relay would be 110v
Voltage drop across start winding 10v
REMEMBER series law (Et=E1+E2…)

17. Solid State relays have a greater range
Example: 1 SS relay may be used for
1/16 to 3/4 Hp motor
3/4 to 2 HP motor
If a current coil was used different relays would be needed.

21. Types of Solid State relays
Two wire is relay only
Five wire is start capacitor, relay and overload
Testing:
When Ohmming them out, a good relay will have a (low) resistance reading
Must cool down before testing

24. Operates from voltage created by start winding Also known as
Potential Relay
Operates from voltage created by start winding
Also known as
Back Electromotive Force, or Back EMF
Operation
Contacts are N.C. and allow full voltage to start winding

27. All other terminals are blanks
Terminals that are used and how to wire potential relay (this is the ONLY way)
Line to start capacitor
Start capacitor to TERM #1
TERM #2 to start winding
TERM #5 to common terminal
All other terminals are blanks

29. Checking the Potential relay with Ohmmeter
Term #1 to Term #2
Continuity
Term #1 to Term #5
Ohm Reading
Ex. 2k ohms
The same for Term #2 to Term #5