Air Cond. compressor motor starting capacitor

[Merc]

We came home from the cottage today to find the temperature inside the house in Pittsburgh was a steamy 84 degrees F. The air conditioning unit was installed on my furnace in 1995 so it’s not exactly state-of-art, but it works so I won’t replace it until it becomes too costly to repair. I checked the 220 volt air conditioning circuit breaker and it was tripped.

The problem this time and many prior times was the failure of the motor starting capacitor on the compressor. I have replaced it many times before so keeping an extra capacitor on hand is a necessity. The original capacitor lasted for about 8-10 years and the replacements fail every other year. I’ve tried several different brands but they all failed every other year. They all have one thing in common. You guessed it - all were made in China.

The capacitor that I just installed was made in the USA by Turbo 200. I won’t know for two years whether or not this one will last longer than two years, but you know Einstein’s theory of insanity is doing the same thing over again and expecting different results.

Any DIYrs out there with similar problems?

[togor]

Our unit is a Heil, from the 1980s, which, knock-on-wood, keeps going strong. The only issue was an AC contactor that was corroded by mouse piss. I plugged the access holes with copper scrubbies and no mice problems since. Two winters ago the furnace guy wired the AC control circuit wrong when he wired in a new furnace but I untangled that myself without trouble.

Regarding your starter cap, it's important to size it to the application. Higher uF ratings will also mean a higher current rating for the device, which is good. But too many uF can be bad also. This web page might be useful.

https://inspectapedia.com/electric/M..._Selection.php

And...kudos for fixing it yourself!!!

[Merc]

It’s good to have knowledge of all things electrical.

My furnace guy says my AC unit could go on for many more years and saves me money every day by continuing to work.

Older gas furnaces, on the other hand, can be dangerous. The heat exchanger can develop cracks and allow carbon monoxide to circulate into the house. It happened to us 2 years ago. Our carbon monoxide detector sounded off and warned us.

[PaFrank]

I had the same problem last year and it turned out to be the fan motor that was seizing and drawing too much and burning out the capacitors. Replaced fan for $85 bucks and not i can hang meat in my house... AC was installed in 1971

[Merc]

Come to think of it, I also had to replace the main contactor, probably 10 or more years ago. It was the only other problem I’ve had with the unit. The old and new furnaces and AC unit were made by Bryant.

[Merc]

I had the same problem last year and it turned out to be the fan motor that was seizing and drawing too much and burning out the capacitors. Replaced fan for $85 bucks and not i can hang meat in my house... AC was installed in 1971

Yes, the multi range capacitor starts both fan and compressor.

[Sunray]

"...and it was tripped..." Probably due to the much higher temps in the house with said house being closed up while you were away. Might be the same issue with the capacitor.

[togor]

"...and it was tripped..." Probably due to the much higher temps in the house with said house being closed up while you were away. Might be the same issue with the capacitor.

Usually inrush is the killer.

[Merc]

Without extra electrical energy provided by the capacitor, the motor won’t spin on startup. It’s trying to start under a physical load of the refrigerant. I can hear the motor humming for a few seconds and then it kicks out on its own internal thermal overload switch. The thermal overload cools down after a few seconds and reconnects power and the motor hums again but won’t spin under the refrigerant load and the thermal OL kicks out again. This repeats a few times until the 220 volt circuit breaker finally sees enough heat to trip. Physically, without capacitor assisted starting, you’d need a motor many times the size of my AC compressor motor to be able to start under load.

The washing machines from years past had a start winding and a run winding that allowed it to start under a physical load. The start windings drew a lot more current and provided more torque than the run windings but were controlled by a centrifugal switch that would switch to the run windings after the motor started to spin.

[Clark Howard]

AC units of that age are so inefficient compared to modern units of the same capacity. Capacitors need some "help" from other components, (compressor, fan, etc.), in order to fail so regularly. The problem is finding an AC contractor who is willing to install a new unit without having you pay for his new boat, truck, or cottage on top of the installation cost.