Knocking from AC carrier 38CKC060300

[printgoon]

Hi have a new home home and last year the AC unit would intermittently knock very loudly..it sounds as if it has thrown a rod(if it was a combustion engine). When it has been especially loud only warm air blowns. I have visually inspected it and the fan is turning freely. It may cycle 3 to 15 times between the times it knocks loudly. I have had it serviced every spring, including a week ago, all the techs have been advised of this problem, for which I receive the response.."yeah these units are known for being loud" when I advise that warm air blown during the "loud knocking " times they get a wierd oh crap look. Any ideas, I am in central cal and when its 100 degrees and 6 days out for a repair visit I would rather have a part replaced now. Last summer I had someone watching my home when he heard a loud bang, in which they replaced 2 switched to the toon of $300 bucks. I had the loud knocking before and after the repair. Any ideas?

[jb8103]

Intermittent knock? Steady knock, like a rhythm? How long does it last? Is the condensor fan running smoothly during the knocking, or look like it is starting and stopping? Can you observe the behavior of the contactor? Don't do this if you have never been around 230 VAC before.

Short cycle protection delay circuit failure...maybe...?

Only data I can find is for a 50 Hz unit.

[ACtechGUY]

You never said how old the unit is. Age of a unit is helpful sometimes. The serial number has the date (week)(month)(year)(example -1 6 98 ) first week of June in 1998 ( in the first 5 or 6 digits) . Units older that 10 years are subject to failures.

What you describe is a major indication that the compressor is failing. Something is coming loose from time to time in the compressor. Sooner or later that something is not gonna go back where it belongs, and then you have no cool - forever.

The KABOOM !!!! noise your housesitter heard was likely a start capacitor (or a KICKSTART) exploding . It can be kinda errrrr......explosive sometimes .

The kaboom was unrelated to your knocking problem. It is as simple as the compressor is broken and needs replacing.

SORRY.

[jb8103]

I suspected it might have been slamming on and off, but a faulty compressor is a much simpler explanation. Occam's Razor.