HVAC Air Conditioner DIY repair question

[Stormin Mormon]

Hum, click. Fails to start.

- . Christopher A. Young learn more about Jesus .

. .

[Ignoramus4261]

OK, thanks. If the capacitor does not work, and the breaker does not trip, then the motor will burn out. Right?

[trader_4]

The overcurrent protection and/or thermal protection in the unit should prevent it from burning out. That's the primary protection in an AC unit, not the breaker in the panel, which is typically sized larger.

[default]

If a cap opens up completely and it is a start or run cap the motor will not turn or may start then stop and start until some circuit protection kicks in. A weak run cap may drag along before it comes up to full speed.

In the case of an electrolytic which has lost some of it's capacity due to age/heat it will pull more current and take longer when it starts until the capacity falls low enough that it will not start.

You did mention something about not knowing the charge in the system so that may affect starting too.

Fans typically don't have starting caps but they may have running caps. The whole idea is to shift the phase angle of some of the windings to emulate multiphase operation from a single phase motor. It is more efficient then shifting the phase with shading poles (essentially shorted windings that can also shift the phase/ cause the motor field to rotate).

In the near future all AC compressors will be rotary styles and use variable frequency drives (sometimes called "inverter technology" in HVAC-speak) and three phase motors. They are the most efficient drives and allow things like running at only the speed necessary to meet demand, as well as "soft" start and stop and they convert single phase to three phase.

Almost no new window AC's do this but many central air and most new mini-split systems do. As efficiency standards tighten all AC's will use this technology. It is already cost effective, unless you are a manufacturer who has old stock piston compressors or hasn't learned the new economies that can be realized from variable speed drives.

If I sound like an evangelist, it's because I ditched my former AC and went to mini split and reduced my power bill by an order of magnitude. The only advantage that central air has over mini split (other than some unsightly wall mounted evaporator unit) is the noise of a mini split - it can't match a central air system that is well isolated with fiberglass ducting.

[Paul Marks]

In my case the capacitor failed, what I saw was the compressor would not turn over and the fan did not turn as well (two part cap), Lennox Elite

11 unit. My UPS software logged the load caused 120 volts in the house to drop for a moment to 113 vac until the compressor safety tripped out.

[clare]

Not if the thermal protection device on the motor is fully functional.

[Stormin Mormon]

Not guaranteed. Some times the overload goes, and some times it just keeps trying.

- . Christopher A. Young learn more about Jesus .

. .

[TomR]

I don't know much about HVAC, and I don't know the answer to that question. But, here is what happened to me as a layperson in a house that I own. The occupants said that the A/C wasn't working and they smell something burning. I, of course, told them to turn the HVAC off and then I went there to check things out. When I turned the A/C on, I could hear a humming sound and I did smell a slight burning. No circuit breakers were tripped, and it seemed like the humming would continue unless I turned the unit off. I turned it off and called our utility company because we have what they call a WorryFree service contract with them for the HVAC. They came out and it was a bad start capacitor. They replaced the capacitor and everything was fixed.

The point is that I assume that if the start capacitor is bad, it does not necessarily mean that any circuit breaker or other protective device will shut things down. I don't know if the motor would have burned out if I left the power to the HVAC on, and I don't know if the burning smell was from the motor or the capacitor.

[Tony Hwang]

Some caps have polarity specific, some don't. Their use is circuit specific. Latter can replace former, not the other way around. I always keep critical parts on the system as spares. HSI for furnace, caps for ODU, etc. Mr. Murphy strikes me usually on week end, LOL!

[Tony Hwang]

You'll smell first. Most motors have imbedded OL protection thermal switch. This is self resetting when cooled off. Better not keep trying which will finish the motor winding.

[Tony Hwang]

Hi, Real important point is to understand what starting cap. does?

[hrhofmann]

Glad to see lightning spelled correctly, an earlier poster spelled it lightening, which is what Michael Jackson did to his skin.

[Stormin Mormon]

Sigh. Now the conversation has really sunken.

What do MJ and residential AC have in common?

Both used to be cool, but are now broken down old relics.

- . Christopher A. Young learn more about Jesus .

. .

[Stormin Mormon]

How do you repair central AC, and Michael Jackson?

Some thing about the dried up little black thing that doesn't want to start any more.

- . Christopher A. Young learn more about Jesus .

. .