I turned on my AC few hours ago and set to blower to ON, as opposed to AUTO. The temp hasn't reached the set point yet, so the AC has been running since I turned it on.
I was down in the basement doing some stuff (unrelated to the AC) when the blower stopped. Curious, I went upstairs to check the thermostat and it was calling for AC and the blower was still set to ON.
I went back downstairs and after about 20 seconds the blower came back on. I don't think it was off for more than a minute. This is the second season with the AC and I don't recall this happening before, but since it was off for less than a minute, who knows?
Blower motor may have a thermal protection device (in the windings). If that is tripping (and then resetting after cooling off), it's not a good sign.
The motor may need lube or the blower may be overloaded from excess static pressure or running at too high a speed. Have a peek at the filters too.
Thermal protect built into the motor comes to mind but less than a minute seems too quick for it to cool down and reset. Keep an eye on it because no, blowers do not take breaks especially with the fan set to "on".
In the summer of 1980, I was working in a place that did injection molding (some very hot machines). The big fans kept stopping and starting. I seem to remember them being off for less than a minute.
- In the summer of 1980, I was working in a place that did injection
- molding (some very hot machines). The big fans kept stopping and
- starting. I seem to remember them being off for less than a minute.
Ah, that explains it! When I said "I was down in the basement doing some stuff", it just happened to be injection molding that I was doing! So, if I stop using this machine, my AC blower will stay on?
Must be a very deep basement for all your equipment.
It is also possible the power company had a drop in voltage that could cause that to happen too. Hard to track that down if it was momentary. If it keeps happening you may want to check the voltage with a good meter, after checking what others suggested, lube and filters.
It _may_ not be a good sign. Depends on what the controller thinks it's doing.
Blower motors consume _less_ power when their flow is restricted, and generally run cooler. They consume more power the more air they move.
I built an air cleaner system. It was a 1/2HP blower motor in a wooden box with three stages of 16"x20" filters (1", 2" and 4" thick). The blower was originally part of a forced-air cooling system for a computer or some such that _needed_ the flow restriction of ducting to operate properly. It would operate for about 20 minutes then shut down for 5 minutes because the motor overheated. Putting a flow restricter that blocked about 1/3 of the inlet of the blower solved the problem completely.
So, that's not it.
It'd be a good idea to wait for this to happen again, and put your hand on the motor casing to see how warm it gets. If it's the thermal trip, I'd expect the motor casing to be very hot when it trips. The motor got extremely hot in my air cleaner until I thought to obstruct air flow. Now it runs quite cool.
If it's a thermal trip, it's more likely to be a stiff bearing somewhere rather than anything to do with air flow (because they were engineered together, and should be just fine). May need lubrication.
I have a question about my blower that might explain what is happening
-
The furnace is a Ruud 90+ 2-stage unit. With the fan switch on the t- stat set to ON, the fan runs constantly at the low speed, but when the t-calls for cooling, many times (always?) the blower runs at high speed.
Is it possible that when the t-stat calls for high speed fan operation, it overrides the ON setting, turns the blower off for a few seconds (
-- Yes, the blower (can) operate at different speeds for different stat
-- settings
Thanks, but that's not what I asked.
What I asked was this:
If the blower was constantly running at low speed because the fan switch is set to ON, would it briefly shut off (i.e. stop for 20-30 seconds) before switching to high speed if the stat called for A/C and high speed blower operation?
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