The starting relay provides power to the start winding of the compressor during start-up for approximately three seconds. At this time, the compressor reaches about 75% of its running speed, the relay shuts off the power to the start winding, and the compressor run winding continues to run the motor and bring it up to its normal speed. (See fig. 46.)
These relays, used in residential units, are mounted on the compressor terminals under the terminal cover. Basically, they are of two types: those with two electrical terminals and those with three. In both cases, they are connected directly to the compressor run and start terminals.
NOTE: Pay particular attention to the word TOP on start relays. If relays are not mounted right side up, they will never open the circuit to the compressor start winding, causing the winding to burn.
TESTING RELAYS WITH TWO TERMINALS: (See figs. 46 and 13)
1. Disconnect the power supply.
2. Remove the access cover in the back of the unit.
3. Remove the plastic compressor terminal cover.
4. Pull off the relay from the compressor and disconnect its terminals from the wiring.
5. Inspect the relay terminals for burn discoloration and the lead wires for charred insulation. If so, replace the relay. If not:
6. Set the ohmmeter to the RX1 scale and zero the meter.
7. Holding the starting relay in one hand with the TOP up, place the ohmmeter probes in the relay terminals. The meter should register a continuity reading. Otherwise, the starting relay is defective and should be replaced.
8. Turn the relay upside down and place the ohmmeter probes in the terminals. The meter should register an open-circuit reading. Otherwise, the relay should be replaced.