I just bought a house and found the A/C unit not working. I
checked the filters and they were as filthy as you can imagine. I
thought I could make the A/C work by simply replacing the filters.
No. After I replaced the filters, there was still no cool air. I
wonder what has been damaged, if any?
Because now, since the fan is doing little if any work, pretty much all of
the electrical energy input translates into core losses and mechanical
friction, resulting in excessive heat generation--and with this all
happening at a time when there is also an insufficient amount of cooling
airflow over the motor, it makes the motor very likely to overheat and fail
in a much shorter time period than its design service life.
Your post is right on!
Yes of course, a clogged filter can by-pass lint and dirt and create all
kinds of high $ problems!
The tech needs to confirm that the evaporator has "an adequate heat-load"
through it before the tech even considers checking the charge!
No system will work properly without adequate airflow of sufficiently warm
air to vaporize the liquid refrigerant as it is metered into the evaporator
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In a previous article "Steve@carolinabreezehvac"
;> It is counterintuitive but "pulling a vaccuum" is easier on the fan than:> moving air. To see that in action try holding your palm against the
:> of a hair dryer. The motor speeds up.
:And do that to a CAH and you get a motor that does not last long..
A forced air HVAC blower motor is an induction motor, and spins at
about the same speed at all load conditions below the point of
stalling. Blower motors sit outside of the conditioned air stream:
They are passively cooled. They should therefore be just as happy
"pulling a vacuum" as they do otherwise.
Afraid not..and it can be proven with a remote tach.
Sorry...matter of fact, every major brand on the market right now, will void
the warranty on a motor that fails due to undersized duct, or bad filters.
How long you been in the biz, or are you just pulling up some website to try
to be right, cause you are wrong, and so is the site.
BTW...there is a reason we carry over 400 different part numbers for AC
units and furnaces..
Oh..how many motors you care to see that sit IN the airstream? Havent seen
a motor located on the outside of the box..ever.
Therefore, you, or the website you pulled that off, is wrong....the motor
does indeed sit in the conditioned air stream...and clue.....its even got
cooling vents on it...some even have heat sinks.
The heat sinks are not there for looks...but give ya a hint why they are
there...its for when you have a commercial installation that you are unsure
that the filters will be changed on a regular basis, and to protect the
motor....GE and Trane used to install them from the factory.
In a previous article "Steve@carolinabreezehvac"
;Afraid not..and it can be proven with a remote tach.
As you can see, the speed of an induction motor does not vary much
around its full-load speed over its useful load range. If you increase
load on it, it slows down a bit and then stalls. If you take away all
load, it doesn't go faster than the syncronous speed, which is only
slightly faster than the full-load speed.
If you didn't understand what I meant before, I said this fact
contradicts your claim by implication that the motor will not last long
because it will spin itself into destruction when the input is
> It is counterintuitive but "pulling a vaccuum" is easier on the fan than
> moving air. To see that in action try holding your palm against the
> of a hair dryer. The motor speeds up.
And do that to a CAH and you get a motor that does not last long..
As any speed up from reducing the load will be quite minimal.
Certainly if the motor is completely enclosed and there is no air
circulation, the motor can overheat no mater what load was placed
on it. If that is the case, that should have been your answer to "blue".
As it is, with the input blocked, and somehow I can get the normal
amount of cooling to the motor iself by whatever mean, the motor will
run continuously for its designed service life -- because it is not
putting out more heat than it is designed to and not running faster
than it is designed to.
You are right I am just surfing the web for information, and I have
came across several cases where the motor is outside of the conditioned
air stream without seeing one that does it differently. You are
welcome to post your own link.
If they are in the conditioned air path, I would have to wonder why it
was done that way. Certainly the motors themselves are quite rugged and
can operate at a temperature far exceeding that expected in the air
handler. They have small internal fans and have no problem at all
dumping heat into the air even in a hot attic. Why cut down the
cooling efficiency of the whole system by, in effect, using the
evaportor to cool the motor.
No...it should not have been.
Care to post YOUR credentials in this line of work? You can post shit off a
website all day long, that wont make it right.
Go to www.trane.com, www.yorkupg.com, www.carrier.com,
www.goodman.com....the list goes on and on...
EVERY single unit made today has the blower motor IN THE AIRSTREAM.
God are you that dense? What do you do for a living anyway? I own a
sucessful HVAC company...one that purposely trains its techs NOT to do the
normal hit and run shit you people are used to...one that does not have to
post anything in here and can and should prob leave you to the likes of
Dave, and Stormy...since they tell you what you want to hear, not the actual
Lemmie guess....you are simply trolling at this point....and you are not in
the trade....bah...believe what you want. You have one (by your admission)
ancient pos furnace that has a thermocouple..you know...stone age units.
Todays units are nothing like that, and if you dont have a clue, and so far,
you dont, dont bother a reply.
In a previous article "Steve@carolinabreezehvac"
:> :;> ;Afraid not..and it can be proven with a remote tach.
;> http://www.engin.umich.edu/labs/csdl/ME350/motors/ac/induction /
;> As you can see, the speed of an induction motor does not vary much:> around its full-load speed over its useful load range. If you increase;> load on it, it slows down a bit and then stalls. If you take away all:> load, it doesn't go faster than the syncronous speed, which is only;> slightly faster than the full-load speed.
;> If you didn't understand what I meant before, I said this fact:> contradicts your claim by implication that the motor will not last long;> because it will spin itself into destruction when the input is:> blocked:
:I know what you said, and I say you are still wrong...
Could you at this point explain what you believe that I have
said to be wrong? Was it -
1) An underloaded induction motor will not speed up to the point of
self-destruction or significant accelerated wear?
2) If the normal operational amount of cooling is maintained to the
induction motor (as in the case where the motor is outside), a blocked
input (which "Blue" says to have the effect of reducing the load on
the motor) will allow the motor to coninue to function to its designed
If the filters were VERY dirty, the system could have been pulling in air
from any leak and/or tear in the duct work.since most is not sealed
This will lead to the evap coil being covered in the same mess that you see
on the filters.
This will cause:
Compressor failure, or fan motor failure.
The compressor can fail due to the evap coil icing over. This leads to
liquid refrigerant being sent back to the compressor, and the valves in most
units, (piston type) are reed valves. While the compressor may be running,
it may not be pumping, and this will cause a lack of cooling.
It can also lock the compressor up, and a replacement in either case is the
fix. The compressors lock not due to refrigerant lock, but due to the oil
being washed off the bearings. Think automotive style crankshaft, turning
two pistons at about 1750RPM, or more, bathed in oil, and then the oil is
The blower motor may fail, NOT due to load as there is no load with dirty
filters, but from lack of load. The motors are designed to run at a
particular static pressure, and without the load, the blower speed actually
increases, and with lack of air, the unit overheats.
Get a legitimate AC company out to give it the once over, and make sure that
they check the condition of the return duct, the evap coil, blower etc...
If its all in working order and the compressor is runnning, and the outdoor
fan is as well, and they claim its low on refrigerant, find out WHY...as in,
if its low, WHY since its a sealed system. A dirty evap coil, or lack of
airflow will cause the techs gauges to read low, but the gauges are only ONE
tool used to determine if the systems low. If all the tech does is slap
gauges on the outdoor unit, and proclaim its low, tell him to take a hike,
but be sure to tell him why.....subcool, or superheat, readings HAVE to be
taken to determine if the units low. Without those calculations NO ONE can
tell you HOW low, or how overcharged a unit may be....and if the previous
owners only had someone come out that didnt check the filters, or evap, and
they were that dirty, its possible as can be that the tech simply
overcharged the system not knowing, (not having the training, or caring
enough to check) that the airflow over the evap was reduced.
Have the entire system serviced...and if its over 15 years old, seriously
consider investing in a new higher SEER unit, keeping in mind that Jan 1st,
2006, the minimum standard will be 13SEER...tomorrows cheap unit is a higher
SEER unit of today, so look into a 14 or better SEER rating, and remember,
that if you go that route, if the company does not change out the indoor
evap coil, they simply took your money and ran.
On Sun, 21 Nov 2004 20:05:03 -0500, "Steve@carolinabreezehvac"
It is highly unlikely that your problem with your AC not working
was caused by the filters being filthy.
Filters being filthy does cause highly inefficient operation though,
so they should be changed regularly to lower your utility bills.
LOL...while you are correct, to a point, tell that to the people that called
us today as a 3rd quote...filter got sucked into the evap, they didnt know
it.....had been there for 3 years...
One new heat pump....it CAN indeed happen, and you would be surprised how
many we see that have been run like that, the other techs didnt check things
properly, overcharged the unit to the point that the unit was in a floodback
condition, and it kills the units.
Somehow I think the bigger problem here is that the OP didn't get a
home inspection done before buying the property. That inspection
would have found this problem. Why people fail to do this is beyond
me, because it is free in most cases. A routine inspection will
usually uncover more than enough problems to get the seller to
discount way more than the cost of the inspection.
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