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re: Reasons an AC would intermittently not blow cool?

Posted on 8/4/26 at 6:32 am to
Posted by Ricardo
Member since Sep 2016
6799 posts
Posted on 8/4/26 at 6:32 am to
Glad you got it sorted out. I have an older programmable thermostat in my house and it works fine. It's not a complicated task to switch them out.

Just make sure you are pretty gentle with those wires. If you break the insulation on a wire (even a little bit) you can cause a short that will have you pulling your hair out trying to figure out why.
Posted by trident
Member since Jul 2007
4871 posts
Posted on 8/4/26 at 6:58 am to

I think there's a decent market for thermostats that look like Nest units, but zero smart features.
Sensi 2

This is what you want. Its only wifi, programmable settings, have it on my house and it works great and have had 0 problems so far. its not a "learning" thermostat like Nest, just a digital one you can use from your phone

Posted by AlxTgr
Kyre Banorg
Member since Oct 2003
88289 posts
Posted on 8/4/26 at 9:27 am to
quote:

Well I'll be F'd. I just checked my settings and I was "automatically enrolled" to something called Airwave that does exactly what you described. Shutting down the compressor and using the fan to distribute air to "save cooling costs."
Wow. Mine has never done that to my knowledge other than it blows a bit after the compressor is off and i always assumed that was to get every bit of the cold air to the rooms. Where do i find this setting?
Posted by Ingeniero
Baton Rouge
Member since Dec 2013
23757 posts
Posted on 8/4/26 at 10:21 am to
If you go in the Nest app, click the gear in the top right, it's under the Nest Sense heading. I also turned off eco temps.

There are claims online that the Airwave setting won't kick in if your house is too warm or humid, but it seems like that's exactly what was running. If I run into the problem again I can rule out that setting and will call an HVAC guy
Posted by TU Rob
Birmingham
Member since Nov 2008
13622 posts
Posted on 8/4/26 at 10:28 am to
I love my Honeywell thermostat. It doesn't have any of these features, it just has timers you can set for temps, and you can set the fan to auto so it only runs when the A/C is running, circulate so that it will also blow while it is off, or on so that it runs continuously.

That being said, since we're talking A/C issues, what would cause a slimy gunk to accumulate in my condensation drain pump? I've been using a drain line cleaner liquid in there about once a month, but once or twice a year I have to take the lid off and shop vac out some gunk.
Posted by CrawDude
Baton Rouge
Member since Apr 2019
6071 posts
Posted on 8/4/26 at 12:05 pm to
quote:

That being said, since we're talking A/C issues, what would cause a slimy gunk to accumulate in my condensation drain pump? I've been using a drain line cleaner liquid in there about once a month, but once or twice a year I have to take the lid off and shop vac out some gunk.

Posted by TU Rob
Birmingham
Member since Nov 2008
13622 posts
Posted on 8/4/26 at 12:10 pm to
quote:

CrawDude


Interesting. So I did a little reading, and should probably switch up what I'm using to flush the lines out. Would a small piece of copper in the drain pan help?
Posted by CrawDude
Baton Rouge
Member since Apr 2019
6071 posts
Posted on 8/4/26 at 12:18 pm to
quote:

Would a small piece of copper in the drain pan help?

I’ve heard of people doing that with the newer 100% aluminum evaporator coils, including HVAC techs, how effective it might be I don’t know, but I don’t see any significant downside in trying.
Posted by TU Rob
Birmingham
Member since Nov 2008
13622 posts
Posted on 8/4/26 at 12:35 pm to
quote:

I’ve heard of people doing that with the newer 100% aluminum evaporator coils, including HVAC techs, how effective it might be I don’t know, but I don’t see any significant downside in trying.


Think I'm going to try it. My air handler is in my basement garage, so I have a PVC tube that drains into a pump, which pumps it up and out in some clear tubing. I've been using a liquid cleaner to keep the lines clean, and haven't had any issues with them getting clogged since I started doing that, but every so often I'll hit the pan with a shop vac. It is fairly small, and only really happens in the hot humid months. I check it when I change my filters and last week noticed the gunk in there. It was thin, maybe only a half inch thick, and in one corner of the pan about 2-3 inches across. I've got some copper pipe fittings I'm going to put in each corner and see how it does the rest of the summer.
Posted by AlxTgr
Kyre Banorg
Member since Oct 2003
88289 posts
Posted on 8/5/26 at 11:08 am to
quote:

There are claims online that the Airwave setting won't kick in if your house is too warm or humid, but it seems like that's exactly what was running. If I run into the problem again I can rule out that setting and will call an HVAC guy
I looked into it. Unless I am reading it wrong, this is just a feature that blows the remaining cool air out of the system. Mine was on, and I never have problems like what you were describing. I do notice the blower remaining on after the outside unit shuts off, but it's a very short period of time.
Posted by Ingeniero
Baton Rouge
Member since Dec 2013
23757 posts
Posted on 8/8/26 at 5:54 pm to
Alright, I think it's a capacitor. It stopped blowing cool again today so I went outside to check. Fan is blowing but compressor was off.
Posted by DMAN1968
Member since Apr 2019
13798 posts
Posted on 8/9/26 at 5:12 am to
quote:

I think it's a capacitor

Home Depot now carries capacitors...It's an easy change out...you can have it fixed in no time.
Posted by UptownJoeBrown
Baton Rouge
Member since Jul 2024
12891 posts
Posted on 8/9/26 at 7:52 am to
You can check if a capacitor is good if you have a multimeter that can measure capacitance.

They can look totally normal but be losing it’s capacity carrying charge.
Posted by Ricardo
Member since Sep 2016
6799 posts
Posted on 8/9/26 at 9:36 am to
If you're going to change out the capacitor make sure you take some pictures of the wiring, and follow the steps to change it out.

It's not difficult, but as long as make sure there's no power going to it and short the leads before touching it you'll be fine.

I recommend taking the opportunity to clean everything up while you're at it. Use a shop vac and get rid of all the spider webs, leaves, dirt, etc.

Be gentle with the wires. The heat and exposure will make them brittle. I use needle nose pliers to grab the leads to pull them off the capacitor.

Secure the capacitor. You can buy some metal strapping and screws to keep it firmly in place.

When putting the cover back on, make sure you aren't pinching any wires.
Posted by Clames
Member since Oct 2010
20190 posts
Posted on 8/9/26 at 8:12 pm to
quote:

If you're going to change out the capacitor make sure you take some pictures of the wiring, and follow the steps to change it out.



That but also know what exactly you are looking at too. Combination capacitors always follow a standard convention where C=COMmon=4 tabs, H=HERMetic=3 tabs, & F=FAN=2 tabs.

quote:

It's not difficult, but as long as make sure there's no power going to it and short the leads before touching it you'll be fine.



Capacitor can hold a pretty good zap even with the unit deenergized, can use a screwdriver to short the capacitor terminals against each other to avoid finding that out the hard way...


For the sake of general knowledge, here's a diagram that shows how to test a capacitor while the condenser is running which is what I do before and after the cooling season. Better to change a capacitor that is getting weak before its a problem and it also keeps the fan and compressor motors happy.




Posted by cajuns td
Prairieville
Member since Jun 2019
315 posts
Posted on 8/10/26 at 4:31 am to
quote:

was "automatically enrolled" to something called Airwave that does exactly what you described.


My ac did the same thing Friday night. Blower only was running. Hasn't done it since though. I suspected either thermostat, capacitor or contactor issue, but just checked and I was also enrolled in this. Probably deleting this thermostat now
Posted by baldona
Florida
Member since Feb 2016
24549 posts
Posted on 8/10/26 at 1:06 pm to
quote:

Alright, I think it's a capacitor. It stopped blowing cool again today so I went outside to check. Fan is blowing but compressor was off.


Have you cleared your condesation drain lines? I hate when this is done, but its not uncommon for AC tech's to wire the float switch to the compressor and not the thermostat. So the system seems to be running normally it just doesn't blow cold air.

I prefer them hooked to the thermostat so that if the thermostat doesn't have power its a fairly quick and easy trouble shoot.

Its not uncommon for a minor clog to allow water through, so the unit will run for a bit and then stop cooling and cycle on and off.
Posted by Ingeniero
Baton Rouge
Member since Dec 2013
23757 posts
Posted on 8/12/26 at 4:36 pm to
Capacitor was shot. It had actually mushroomed up since the first time I opened the panel to check. It was reading 3uF so I got it swapped out

We're cooling now
Posted by UptownJoeBrown
Baton Rouge
Member since Jul 2024
12891 posts
Posted on 8/12/26 at 4:38 pm to
quote:

Capacitor was shot. It had actually mushroomed up since the first time I opened the panel to check. It was reading 3uF so I got it swapped out We're cooling now


Great job! Also thanks for posting the problem and resolution. Helps us all how to troubleshoot issues.
Posted by OT_10
Northshore
Member since Sep 2016
265 posts
Posted on 8/13/26 at 9:26 am to
I have a similar question hopefully someone on here can help with. My vents blow 104-105 degrees until the outside fan kicks on then cools down to what it is supposed to do. This heat pushes through vent for 5-10 mintues. The AC company changed the thermostat and a defrost board so far and try telling me warm air will come throught until the fan kicks on which sounds like they really have no clue what it is doing. Any help would be appreciated.
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