HVAC Fan Running

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SpeedThrills

SpeedThrills

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We haven't used our AC for 3 weeks. When I got up this morning, I noticed the fan running. The thermostat is the typical programmable battery powered box store thing that is about 15 or 20 years old.
I don't know much about these systems, but I would imagine if the unit had been running, and the fan didn't shut off, it would be a limit switch or relay or?
But what would cause the fan to start running by itself?
I cycled the stat through the heat, ac and off again. No luck.

I just took the batteries out and it stopped. Is it the stat?
 
I ordered a new stat. The one we have was acting up last winter. We use the programming feature for the heat, and it wouldn't start on its own on a Monday morning. lol After a little help, it ran fine all week, and weekend. The ac, it's either on or off.
My wife likes the stat called, "The Nest", so one is on the way. My step-daughter has one and likes it.
 
Many of these stats use pretty small relays which can become welded contacts, and some use solid state devices like transistors or SCRs and those can fail

One time a service call, complaint was "no cooling." This was a one time customer and we had not installed the system so I was unfamiliar. Before I entered the office building, I checked the 5 OD units and was unsure, because not all were necessarily "calling." But one the suction line was VERY VERY warm, and it was not a heat pump!!! Turns out the office people had bought a bunch of cheap import "setback" stats and one had failed, bring BOTH heat AND cooling on at once!!! The furnace was heating and the AC was "trying" to cool!!! LOLOLOL
 
Mike69cuda said:
Does it have a switch to run the fan all the time?
Click to expand...
When I started running the ac last night, I noticed that it had switched from "auto" to "run". Maybe that was because I had the batteries out all day. I didn't notice what the fan was set on before I pulled the batteries. But, like I said, the fan was running on its own yesterday morning, and it has always been on "auto". But it was running on its own.?

67Dart273 said:
Many of these stats use pretty small relays which can become welded contacts, and some use solid state devices like transistors or SCRs and those can fail

One time a service call, complaint was "no cooling." This was a one time customer and we had not installed the system so I was unfamiliar. Before I entered the office building, I checked the 5 OD units and was unsure, because not all were necessarily "calling." But one the suction line was VERY VERY warm, and it was not a heat pump!!! Turns out the office people had bought a bunch of cheap import "setback" stats and one had failed, bring BOTH heat AND cooling on at once!!! The furnace was heating and the AC was "trying" to cool!!! LOLOLOL
Click to expand...
That's funny! A losing battle, for sure. Mine isn't that bad, but I do think it's the stat. I figure I'll try that, since my wife has wanted "The Nest" ever since her daughter got one. Happy wife, happy life!
When I started the ac last night, it ran the temp down to the setting, then the fan stayed running (again), when the compressor shut off. I had switched the fan to "auto" (mentioned above), but it didn't care. I cycled the fan switch a few times to see if it had some dirt I could clean off, but it didn't respond. However, before I went to bed, it was working normally, and still is this morning. We have family staying for a few days, and it's behaving. I'll leave well enough alone, until they leave.
All a bit convoluted. Bottom line: I think the stat is bad.
 
We have a Nest thermostat, but we have all the smart stuff turned off. I don’t like things that think they are smarter than me (Lot of stuff, I know). If you want it to learn your daily pattern & adjust for it, you might like it….until you don’t.

I don’t want google controlling my home temp. But I am just a cranky old guy…..
 
Mike69cuda said:
We have a Nest thermostat, but we have all the smart stuff turned off. I don’t like things that think they are smarter than me (Lot of stuff, I know). If you want it to learn your daily pattern & adjust for it, you might like it….until you don’t.

I don’t want google controlling my home temp. But I am just a cranky old guy…..
Click to expand...
I'm right there with you. I'll turn off whatever (so-called) "smart" stuff it does. (ssshhh) I don't know much about it, but I like being able to adjust temp before you get home from a phone. (like after a vacation or just a couple days away)
 
The other thing than can happen is that sometimes various electronics can interact...........I have not kept up with modern thermostats so I don't know "what they are doing," EXAMPLE

Some combo furnace/ central air systems have a delay in the controller so that the fan STAYS on for a PERIOD OF TIME after the compressor shuts down. This is to extract the extra cooling effect "left" in the evap as it is still somewhat cold, and also to dry it out

IF the stat has the same function, you may end up with the fan running for several minutes, after the AC has been satisfied or shut off
 
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