Yet another HVAC question for the hive

[Baldanders]

I had my AC stop working entirely for about 3 hours yesterday.

The stepkids/grandkids were over, and temp started creeping up. My wife and stepson kept messing with the themostat, and eventually, the fan was not blowing at all, even with the setting at "on" not "auto."

I spent 60-90 minutes dicking around with the thermostat and fuse box to no effect. Thermostat was acting like it has turned on the compressor and everything is good. I spent a bit looking up troubleshooting for HVAC, and I went into the crawlspace to see if I could figure out a fix. I found the drainage line for condensation (I think), opened a valve/seal, and the system fired back up in 2-3 seconds. Working fine for 18 hours now, not struggling to maintain 73 on a hot day.

The system got put in about 11 months back, and I am pretty sure capacitor problems and the like aren't a factor, given that the fan was knocked out as well.

Can anyone tell me if my assumption that the drainage got backed up, and I let air into the line, clearing the blockage, has any validity? The sites I was looking at said that systems have breakers/switches that turn the system off if the drainage pan is full. But they all mention having to reset the switch to get the system running again.

My wife thinks I'm a miracle worker, but I am feeling like a clueless putz as usual.

[peterb]

Not an HVAC expert. I just installed a condensate pump for our standalone dehumidifier. The instructions included how to wire the overflow sensor relay to central HVAC controls. As fare as I can tell, the relay would go back to the normal state once the overflow was resolved.

So it makes sense to me that a plugged drain could kill the system, and opening the drain would resolve it.

[Baldanders]

Not an HVAC expert. I just installed a condensate pump for our standalone dehumidifier. The instructions included how to wire the overflow sensor relay to central HVAC controls. As fare as I can tell, the relay would go back to the normal state once the overflow was resolved.

So it makes sense to me that a plugged drain could kill the system, and opening the drain would resolve it.

Damn, that was quick! Thanks. At least my theory is definitely possible. Usually they aren't. I am wondering if I can do anything to make the problem less likely, but it is literally a 1-minute fix. I am only worried it might go while we are at work and our poor dogs would roast.

[TDA]

I’m guessing this is central air and not a ductless system?

It sounds like a thing that could happen. If you unplug the condensate pump on your CAC, for example, you can definitely turn off the AC and moisten your basement.

[Malamute]

Damn, that was quick! Thanks. At least my theory is definitely possible. Usually they aren't. I am wondering if I can do anything to make the problem less likely, but it is literally a 1-minute fix. I am only worried it might go while we are at work and our poor dogs would roast.

There exist temperature alerts/alarms that can be set to text, call or whatever if temps reach a certain point, either hot or cold. If you have a home camera system and have room for a spare camera you could also set one on a thermometer so you could see what was happening as a backup. I was going to set a camera on the sump pump area of dads old house so I could see if it was flooding.

[peterb]

I am wondering if I can do anything to make the problem less likely, but it is literally a 1-minute fix. I am only worried it might go while we are at work and our poor dogs would roast.

Not knowing anything about your system, I’d just say Drainage 101: minimize bends in the drain (& vent?) tube, make sure the slope is good, use as large a diameter as possible, clean crud out of the drain pan/tank, add a second drain, etc.

You can get home temperature monitors or HVAC monitors that will call/text/email if there’s a problem.

[JclInAtx]

Yes, it can be a blocked drain pipe. We have an upstairs central a/c that sits in a drain pan. A couple years ago it stopped running. A/c repair came out and just cleared the drain pipe. Next time it happened I hooked up a shop vac to the end of the drain pipe and that cleared it. When it was installed I was told to pour a mix of 1/4 cup bleach and 3/4 cup water every 3 months to prevent this. I've learned to do it monthly in the summer.

[Willard]

Yes, it can be a blocked drain pipe. We have an upstairs central a/c that sits in a drain pan. A couple years ago it stopped running. A/c repair came out and just cleared the drain pipe. Next time it happened I hooked up a shop vac to the end of the drain pipe and that cleared it. When it was installed I was told to pour a mix of 1/4 cup bleach and 3/4 cup water every 3 months to prevent this. I've learned to do it monthly in the summer.

I also do the bleach (or vinegar) preventative maintenance, but eventually, you'll probably need to clear out the drain pipe again. Not sure the technical terms, but the overflow (in our case under the overhang in back of the house) will start to drip, indicating a blockage and it is time to attend to clear things out again. We've had that twice in 15 years at this house.

[EricM]

Regarding monitoring devices, I have been pleased with the Honeywell Lyric Wi-Fi Water Leak and Freeze Detector (RCHW3610WF). It's a standalone battery-powered device that connects directly to wifi (some other units require a hub or home automation controller, which has its pros and cons). You can configure high/low alerts for temperature and humidity, which are sent to the mobile app and optionally by email. It has a built-in siren for leaks (in addition to the mobile alerts), detecting water at the unit itself and anywhere along an included 4' cable (additional cables can be chained together to extend coverage). If it goes offline, you'll receive a notification about that too. The initial pairing was a pain (just try again if it inexplicably fails), but after that they have been trouble free. I initially bought one to monitor temperature over the winter when we had purchased a home but were not living there until making renovations, then added more for water detection. A couple months ago the grinder went out during the night when the water softener was regenerating, and one of these alerted us before there was any damage.

Many smart thermostats can also send alerts if the temperature goes out of range.

[Baldanders]

Thanks for all the advice. I will be doing some investigating around the drain pipe to try to figure out how everything is working. I`m not sure if there is a pan. (Had to deal with that in an old AC in a restaurant) It looks like the drainage just goes straight to the septic system.

System is still running strong today.