A hard start kit is a combination relay, start capacitor, and overload protector. Primarily, this kit (see fig. 47a) was designed to start older compressors that due to their age and normal wear become hard to start. Very often, a compressor that is thought to be defective can be restored to service by using a hard start kit.
A hard start kit is a great tool for the service technician. It eliminates a lot of work and time spent in testing several components and looking for the defective part when a compressor fails to run or cycles on overload. It is inexpensive and can be used on almost all 115 VAC compressors under 1/2 hp.
Some hard start kits are designed for use on compressors operating on 208-230 VAC and on air conditioners up to several tons. The wires on the kit are either color coded or individually labeled Start, Run, and Common.
HOW TO USE A HARD START KIT
a. Disconnect the power from the unit.
b. Remove the overload protector and starter relay.
c. Connect the start terminal of the compressor to the wire on the kit marked Start.
d. Connect the run terminal of the compressor to the wire on the kit marked Run.
e. Connect the common terminal of the compressor to the wire on the kit marked Common.
f. Find the lines that supply power to the compressor. (Normally, one goes into the overload protector and one to the start relay.)
g. Connect these lines to the remaining two wires on the hard start kit. Plug the unit back in to the power source, and if the compressor starts and continues to run, then the problem is solved. If it does not, the compressor is defective. In which case, remove the new hard start device and replace the compressor.
