My AC system is getting very old and I was wondering if I should add a Hard Start kit and with what spec? Here is my AC spec included below and the existing Dual Run Capacitor is 440volt and 40+5MFD.
Should you just change a cap because your system is old? NO you don’t state there are any problems. Electrolytic capacitors do fail over time but we don’t know what you have. oil filled usually last the life of the unit but are much more expensive and not appropriate for all climates.
If you are noticing the lights dimming , hard starts blowing fuses if all the connections are good replace the cap with the same value.
As electrolytic caps age they loose their ability to hold a charge and or short out (note a bulged cap case has usually shorted, it may be working now but needs to be replaced). As caps loose their ability to hold a charge they can not get the motor started thus dimming lights and blown fuses, let this go in long and the compressor windings will be damaged.
There are lots of film flam guys out there if your system is starting hard the cap just needs replacing with the same size it is that simple (if the cap is the problem). If you could not find the same size +-10% will work but not as well as the manufacturers recommended size.
I also have a 3.5 ton R-22 unit. Mine (a Carrier 12 SEER with a scroll compressor) has been in service for 29 years and is coming to the end of its service life. I am trying to get through one more cooling season but my refrigerant is low judging by the sight glass and the fact that the suction line is not as cold as I think it should be. I figure that I could need a full replacement any day.
I see no reason why you should add a special start kit. Do you have any reason to think it would functionally benefit from this? It won't be cheap.