HVAC AC Capacitor Replacement

Question

I have a Carrier Infinity Series AC Unit (Model #: 24ANA748A0030020 or 24ANA748A00300); its capacitor needs replacement. I live in Chicago; so VAC is 120 x 2.

Current Capacitor Specification: HC96KA055D (model), 2-connectors/pins, 55 MFD, +06 -06%, 50/60 HZ, 440 VAC, Round (DIELEKTROL).

Questions:

1) If I cannot find an exact equivalent, should I consider a capacitor with a higher or lower MFD (than 55) in order to be safe? 2) What is the relationship between MFD and tolerance? Should it go up or down with increasing or decreasing MFD?

Answer 1

1) Higher is better than lower--BUT you do not want to go too much higher. Given the relatively tight (and odd) 6% tolerance on the original, you would not want to exceed 58uF with the replacement cap. The ESR on the replacement cap should be very close to the spec of the original. (56uF is a std value, 55uF is not).

The following is a good reference: https://inspectapedia.com/electric/Motor_Capacitor_Selection.php

I have never seen a tolerance of +/- 6% before.

However, the identical replacement cap you seek is available here for ~$26.

https://www.amazon.com/Capacitor-Round-volt-Z97F9042-97F9042/dp/B005DST0V4

It is spec'd at 42-55uF-- which is ~47uF +/-20%. You may find cheaper sources elsewhere.

2) Tolerance and uF values are completely independent. You can obtain std cap values with Typical tolerances are +/- 1, 5, 10, 20%.

Answer 2

you could get a proper technical answer by asking why do I need a run capacitor and what value in the electrical eng. section.

If a [more] wrong capacitance value is installed for a run capacitor it will cause a [more] uneven magnetic field around the rotor of the AC electric motor.

The more wrong the capacitance value the more off the magnetic field and less efficient the motor will be... more heat, noise, vibration. It's correcting lead/lag of voltage peaks with current peaks in the AC wave form, AC motors are inductive with power factors (efficiencies) as low as 0.5. A [run] capacitor is used to combat the inductance and get the voltage/current peaks to line back up, you will either under correct or over correct when using the wrong [run] capacitance value. So a higher uF rating is not simply better.

How far off is too far... this assumes the original spec'd capacitor by the manufacturer was mostly correct to begin with. So when you cannot find the exact microfarad (uF) replacement then go with whatever is now available that is closest. Don't simply choose a larger uF one over a smaller one. The tolerance value don't take too seriously.

the requirement is that the AC voltage rating meets or exceeds the application, and that the frequency (50/60hz) is correct. For a 240V application the run capacitor will typically be rated to 377 or 440 volt, for a 480v application would be a 600v cap. Then its a matter of getting the correct uF that will correct the lead lag to get the AC motor to operate as near a power factor of 1 (most efficient) as possible. Going a little off the uF original OEM uF rating may help, but which way (higher or lower) one cannot know without test equipment so you would be guessing, so choose the closest uF replacement. And also recognize if it's a start cap or a run cap or a dual cap (start & run in one) so you don't install and incorrectly wire the wrong one. When motor is running on new run capacitor listen and feel for more noise and vibe and if there is then your not correct on your run capacitor choice and need a different value either higher or lower. For your original 55uF cap, choose a replacement between 50-60uF; replacements are usually stocked in increments of 5uF (30,35,40...65,70) so a nearest replacement can be matched when servicing... a tolerance of 5% means a 57uF is no different than a 55uF one... up to you if u want to spend extra on a smaller % tolerance cap vs a larger % tolerance. there is also https://www.homedepot.com/p/Directbrand-2-5-MFD-to-67-5-MFD-Round-Universal-Motor-Run-Capacitor-MUNICAP200/206041447