We've had this Central AC problem for a week or two and I have done hours of research and work on the problem but it continues. I'm going to keep this non-technical to avoid confusion and because I barely know what I am talking about.

During cooling, the outdoor unit's fan will begin making a banging noise after an extended amount of time (sometimes 20 minutes, sometimes an hour). The banging sounds as if a stick had been shoved into the fan. Sometimes the banging has many repetitions (20+ times in 2 seconds) followed by a louder bang. Sometimes it is 5 bangs in 3 seconds. Other times it is just one or two loud bangs.

Usually, after the last bang, the fan whirls normally. Then the banging will come back (if the unit is still cooling the house) in anywhere from 3 minutes to 15 minutes. Occasionally, however, the BREAKER WILL TRIP after one of these bang sessions.


Other info:
I have cleared a blockage that was in the drain (condensation) in the basement and replaced the furnace filter.

I have removed the top of the outside unit multiple times now. There is no damage to the fans blades whatsoever. I have cleaned all debris from inside the unit and gently sprayed water (starting from the inside) on the fins to remove any build up. I have snugged up the bolts that attach the fan to the top of the enclosure. None of the wiring appears to damaged.

I have noticed that there is a 18" section of tubing/piping that completely frosts over during cooling. (Is that normal?)


I am a father of three. My wife stays home with all three including our 4 month old and we are looking at 90+ temps later this week. Any information that you can provide will be greatly appreciated. I plan on calling a HVAC professional today but I'd really like to know exactly what is going on so that I don't get racked over the coals. Thank you.

 

Welcome to the forums.

If there is nothing visually wrong with the fan blades then it must be a motor problem. It may be bearings going bad.

 

Frost on the pipe is not normal. Sounds like you might have two problems. Frost can be caused by dirty filter, dirty blower or low on refrigerant.

 

Fixed! No problem with the condenser fan. The A Coil was frozen over. The noises and trips came from the compressor trying to process water. The HVAC Professional I picked was outstanding, he explained everything that was happening over the phone (in high detail but in a way that I could comprehend it). He told me what to do to fix it and everything to look for along the way.

 

That really doesn't make much sense. Even if the coil freezes due to a dirty filter (or low airflow due to dirty coils or bad air handler fan) it won't cause the compressor to "process water" (whatever that means exactly).

So what did you do to fix it? Clean everything? That's normally the cause of freezing, that and low charge.

 

Odds are your issue is not fixed. They simply got you going again, only to repeat what's already happened. "Process Water" makes no sense.

 

It might still have a low charge but the banging noises and breaker trips have completely stopped.

I replaced the filter, it was very dirty because I had been running the blower consistently since I first encountered the problem 7 weeks ago. Turned the AC off overnight (with the blower on) to allow the coils to defrost. Turned on the AC after allowing 15 hours of defrost time. I then spent the day monitoring everything intermittently.

Everything had to work very hard yesterday to get and keep the house cool. I think it got to 95 degrees with very high humidity. But there were zero problems. It took a little longer to cool than expected but it is really hard to know if a recharge/leak repair is needed because of the high temp and me constantly going outside to check out the condenser. I turned on the AC at 8am the house was 80 degrees. By noon it was 74 degrees but I was turning off the AC every half hour to verify there was no frost forming on the pipes in the condenser. I took the house all the way down to down to 70 degrees and condensation formed pretty heavily on all the windows above the vents.

During all of this no frost ever formed on the pipes in the condenser, no banging was ever heard, no breaker trips occurred. I'm not saying no work needs to be done (I'm sure the blower could use a good cleaning at the very least), but the major issues have been fixed.

It sounded to me like the tech theorized that the banging was caused by liquid going into the compressor, which was caused by frozen coils, which was caused by a lack of clean fresh air. All I really know it that our homes AC is back to normal for now.

 

OK that makes sense now. The liquid he was referring to was liquid refrigerant. That will wack out the compressor.

 

Hmmmmm...... it actually sounds more like the system is low on charge and it was the contactor (and the compressor) that was banging. This problem will be much more noticeable on a cooler day.... so keep an eye on the system when the temps cool off a bit.