I had a nice tech come today, to check our AC for summer duty today. He checked the starting caps among other routine issues. Our AC unit does not have running caps, most AC units do. The starting caps were well within spec.
Before leaving I got the usual upselling pitch. This is not the techs fault, but either managers and or unscrupulous travelling salesmen.
The sales pitch was to purchase add on booster caps to improve the AC starting and prolong the life of the AC.
Not only is this unnecessary, but harmful. This is all similar to speaker technology. An electric motor is a large inductive load powered by AC voltage. Now when powering inductive loads, there are always phase angles between voltage and current. In other words they are not in perfect phase. This leads to the concept of apparent and true power. So when you start a motor there is a large power draw and the large apparent power is provided and given back as the motor speeds up
In a large AC motor like in an AC, there is a high starting current which will drop voltage and cause the motor to struggle to start. This also would shorten the life of the motor and also dims the house lights and is prone to blow the AC circuit fuse at the panel.
To bring phase and current into better phase alignment and reduce start up current starting capacitors are placed in parallel with the motor, to align current and voltage angles. This reduces the discrepancy between true and apparent power and stops the motor struggling to start.
However, that starting cap needs to be he right cap, tuned to the inductance of the motor coils. So the capacitance has to be optimal, no more OR less.
So this sales pitch is harmful snake oil. I gather this is doing the rounds at the moment, and there is good advice the same as mine. Don't fall for it.
The tech was a very nice guy and had lots of questions for me. I explained all this to him, and I'm sure he understood.
Now I'm waiting for a call back from one of the bosses.
The cost of this "upgrade" by the way, was nearly $500.00.
Lastly you should have you AC caps checked yearly, as these large caps will fail over time, and shorten the life of your AC unit. So this is important yearly maintenance for all AC units and other large electric motors.