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.
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
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
Age and Treachery will Triumph over Youth and Skill
On Sat, 07 Jul 2007 16:55:43 -0700, DerbyDad03 wrote:
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.
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.
After you have checked what everyone has told you, then you may want to gave a call the company that installed the furnace and have it checked out.
You never know what they may find, a loose wire, a sticking relay or what ever since it sounds like the furnace is alittle over a year old.
HVAC Service Technician
Energy Equalizers Inc.
turned on my AC few hours ago and set to blower to ON, as opposed to<BR>AUTO.
The temp hasn't reached the set point yet, so the AC has been<BR>running since
I turned it on.<BR><BR>I was down in the basement doing some stuff (unrelated
to the AC) when<BR>the blower stopped. Curious, I went upstairs to check the
thermostat<BR>and it was calling for AC and the blower was still set to
ON.<BR><BR>I went back downstairs and after about 20 seconds the blower came
back<BR>on. I don't think it was off for more than a minute. This is
the<BR>second season with the AC and I don't recall this happening
before,<BR>but since it was off for less than a minute, who knows?<BR><BR>Any
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
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 (<30?) and then turns it back on at high speed? In other
words, it doesn't go from low to high, it goes from low to off to
I may do some testing when I get home tonight, but I thought I'd throw
the question out first.
-- Yes, the blower (can) operate at different speeds for different
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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