Most likely cause for the AC having a bad day?


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Old 07-07-22, 05:07 AM
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Most likely cause for the AC having a bad day?

A few days ago, my AC decided to work poorly, blowing somewhat cooled air still, but not cool enough. Air coming out the vent was 72 when normally it's 58 degrees. I turned it off, ended up with it off overnight, checked the capacitors (they seem fine), and in the end, put the capacitors back and turned it back on. (It was a very hot day, to be fair, but there's a lot of hot days here.)

Then it started (and I'm sure just temporarily) blowing cooler air than before (64 degrees), then the next day, back to 58 degrees out the vent (fluctuating a bit, at times 62).

So, under that set of background info, still (for the moment) working, but with various effectiveness, what do those more knowledgeable suggest as the most likely cause? Thanks.

(FYI, I have a couple other posts on two other very specific topics, but I think they are different enough and specific enough, that this question is better in a thread of its own.)
 
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Old 07-07-22, 05:24 AM
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Hi, are the condenser coils clean, is the large pipe from the condenser cold and sweating, is the small tube hot?
Geo🇺🇸
 
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Old 07-07-22, 06:18 AM
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The absolute temperature of the air coming out of the vents isn't terribly important. What is important is the Delta T, the difference in temperature between the air coming out of the vent closest to the air handler, and the return air intake. If your Delta T is in the range of 15-20 degrees F, your A/C is working properly. The temperature of the air going into the air handler (return) has an effect on the temperature of the air coming out of the air handler.
 
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Old 07-08-22, 07:02 AM
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@geochurchi, yes, pretty clean, I won't say "just cleaned", but quite clean. And yes, cold pipe is sweating, the insulation not 100 percent perfect, but pretty good, and the small pipe is hot.

@bob, I'll check when I have a better opportunity. Thanks, to both of you.
 
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Old 07-08-22, 07:10 AM
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Hi, as stated it important to find the Delta T or temperature difference from supply air at the closes supply vent and the return at the air handler.
 
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Old 07-31-22, 03:56 PM
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I had a few weeks of the AC behaving again. During that time, other aspects of life decided to make themselves big problems too, so I was thankful that the AC worked again for a while, seemingly just fine. (I didn't get to check cooling across the coils due to other things. Overall, the system did return to blowing as-normal cold air directly out of the vents after a day or two.)

Anyway, today, it's blowing hot again. I'm checking filters and so forth in the meantime.

My current theory is freezing, since when I went outside while the outside unit was going, the fan was blowing non-hot air, so those outside coils weren't hot. It's a Heat pump/furnace combo, so I do have to psych myself up to go into the attic when it's 96 degrees outside and about 130 up there, but I'm on my way in.
 
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Old 07-31-22, 04:08 PM
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If the coil is freezing up.... the airflow out of the registers should be extremely reduced to the point where you should be able to feel the noticeable difference.

Can you see the condensate flow ?
If yes.... set the system to FAN ON only and see if the condensate flow increases.
The condensate flow should stop pretty quickly when setting the system to FAN ON unless it is iced up.
 
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Old 07-31-22, 06:06 PM
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@pjmax, I turned everything off for a while. I'll try that.

Earlier, I don't think I noticed a decrease in the air flow, but I wasn't necessarily looking for that before reading your post. There was definitely some air flow, blowing at uncooled or at least higher than normal temperatures.(Today, I didn't spend as much time looking as a few weeks back, then there was definitely about the same air flow as normal.)

Just a reach here, could a dodgy float switch cause similar issues?
 
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Old 07-31-22, 08:54 PM
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New info

It's not frozen. It's ugly, with the brackets holding the coil rusty, but the coils themselves seemingly pretty clean. (Photo attached.) This is about 8 hours since I turned everything off. One thing hard to see in the photo, although if you look closely, toward the bottom the brackets show a faint trace of moisture.

No puddles anywhere, so I don't think (had I checked right when it first acted up) it was frozen.

Getting the darn cover off, and even worse, back in place took the longest time. It's a Carrier Weathermaker with ComfortHeat, and there's a vent duct and assembly about three inches from the bottom of the cover, so there's not room to tilt the bottom out to work the cover back in.

I also just noticed, the condensing unit is about ten years younger than the rest of the equipment. I guess the previous owners of my house had AC adventures too.

 
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Old 07-31-22, 09:02 PM
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I would expect to see some moisture.
Yes.... that is rusted good. Not uncommon especially in high humidity areas.
The ice would be long gone after 8 hours in that heat.

A dodgy float switch would at the very least shut down the condenser.
So if the condenser is running... it's not a float issue.
 
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Old 07-31-22, 09:27 PM
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@PJ, thanks yet again.

Are there other explanations for why it freezes up? (The filter is OK.) My reading articles here says low refrigerant is another explanation. Any other thoughts?

And I guess stuff towels below or whatever I can rig to catch any goop, if I did decide to spray the coils with cleaner?

I am overdue on replacing the condensor fan, doing that this week. Given that it's squealed in the past and the squealing part at least stopped with some garage door cleaner, clearly all isn't right there. It does seem to blow powerfully, but if it were not blowing to specification, could that be a factor? Thanks again
 
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Old 08-01-22, 08:53 AM
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I suffered through years of trying to trouble shoot an old AC that would intermittently freeze up (we must have gone through 4 cylinders of R22 over the years filling and venting that thing).

In the end, when we had decided to run all new lines (because the working thesis was that one had pinched inside the wall) and we were cutting apart the copper we discovered an clogged, unservicable, inline mesh filter with very little outward indication of its existence right before the evaporator. Cutting it out and installing a modern AC filter solved all the problems.

No idea if this is whats going on in your case but just throwing it out there.
 
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Old 08-01-22, 09:07 AM
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A dirty coil or low on charge could cause the coil to ice up.
You can spray right in place. The solution can run down the drain.
Flush well when done
 
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Old 08-01-22, 10:23 AM
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Thanks

@PJMax, my condensor unit is stacked vertically on top of the heat pump assembly, so if there were goop to flush, it would go down into the furnace. To be cautious, I'll rig something up somehow, to limit how much goes down there.

@Esand1, that's interesting. In my case there's at least one filter-dryer in plain sight, is that what you're mentioning? Also, should I be concerned if what I have is a bi-directional heat-pump filter drier, when to my amateurish eye, what I have is a Furnace/AC, not a Heat Pump? Or is a filter is a filter is a filter?
 
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Old 08-01-22, 10:37 AM
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I also have a furnace / ac unit. It wasn’t the big noticeable filter drier, that’s what I replaced it with. It was like a little mesh screen, like a tiny colander inside one of the refrigerant pipes close to the air handler.

I might have a picture somewhere, I’ll look for it
 
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Old 08-01-22, 11:09 AM
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Found the pic

 
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Old 08-02-22, 04:00 AM
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@esand1, thanks. knowing my limitations, I suppose Ill draw my own line at pipes and refrigerant and such. I still want to be informed enough to know what’s likely causing this though

@pj and all, I have confirmed (it stopped cooling again) that the coils did not freeze, so I’m left with the puzzle of what made it work again for a while last month (and keep going for about a month), then two days ago (for about 16 hours)

 
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Old 08-02-22, 12:12 PM
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Probably solved

I’ll find out for sure tomorrow. But for the first time while I was there to watch and witness, I saw the condenser fan NOT spinning. as recently as yesterday and earlier this morning it spun.

I suppose there are still other possibilities, but in my case I do know for sure the fan is and was on its last legs. I pick the new one up tomorrow, then I’ll have more of a definitive answer

Anyway, I’ll report back. Fingers crossed
 
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Old 08-04-22, 09:07 PM
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Solved. Perhaps slightly early to break out the champagne but so far so good

I didn’t get to put in the new condenser fan until today. 13 hours later and all is well though.

the old motor was about to die for real. The daft can be rugged/pushed maybe a half inch of play. The new one is way quieter and although I can’t quantify scientifically, I think the old definitely wasn’t pushing the same amount of air as the exact (I spent the extra on OEM also) replacement.

interestingly, one of my other posts about condenser startup noise was, I’ve discovered, the fan.

Thanks all for the thoughts
 
 

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