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Default AC repair question

I had a problem with my AC units. I thought it was the freon which
was too low.
The AC guy came out and said that he first recommended cleaning the
outside AC units, at $80/unit. His partner says that my units look
clean. He says that they should be cleaned every year.
So he takes off the top casing, washes it with a lawn hose, sprays on
an A/C cleaner (sodium hydroxide based), and washes it off. $300
later, he says that the freon needs to be added too. Ok, another $150
later the problem is solved. I got the feeling I was hood winked and
robbed.
Two questions.
Is washing and cleaning the units standard practice? Is it even
necessary to do it once a year? On my old house, I haven't cleaned
them in 3 years and never noticed a higher than average bill for not
doing so.
How much efficiency is lost by not cleaning the units? The repair guy
quoted 50%, but I made a smart ass remark like 5%/yr.
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Default AC repair question

I had a problem with my AC units. I thought it was the
freon which
was too low.

CY: yeah, everyone says that.

The AC guy came out and said that he first recommended
cleaning the
outside AC units, at $80/unit. His partner says that my
units look
clean. He says that they should be cleaned every year.
So he takes off the top casing, washes it with a lawn hose,
sprays on
an A/C cleaner (sodium hydroxide based), and washes it off.

CY: Hope he left the cleaner on long enough to foam up. I've
worked on plenty of units that "look clean" but aren't. You
have to get the system running, and check some temperatures
to find out if the coils need cleaning.

$300
later, he says that the freon needs to be added too. Ok,
another $150
later the problem is solved.

CY: Hope he left the system running long enough to dry out,
afterwards. The evaporative cooling can throw the numbers
and pressures and temperatures around a bit.

I got the feeling I was hood winked and
robbed.

CY: I can imagine that.

Two questions.
Is washing and cleaning the units standard practice?

CY: Yes, it is.

Is it even
necessary to do it once a year?

CY: Depends how much dirt and dust they pick up. I think
that most cases, every 3 to 5 years is good.

On my old house, I haven't cleaned
them in 3 years and never noticed a higher than average bill
for not
doing so.

CY: Well, if you take the energy bill from three dirty-coil
years of use, they will be about the same. Clean the coils,
and the energy bill should go down.


How much efficiency is lost by not cleaning the units?

CY: I've seen 100% loss of efficiency in units that were
dirty, but looked clean. I worked on one that was simply not
cooling the house at all. After cleaning, it worked great.
The home owner was talking about replacement, but was
willing to let me clean it and see if that helped. It did.

The repair guy
quoted 50%, but I made a smart ass remark like 5%/yr.

CY: The repair guy was a lot too low.


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Default AC repair question

In article ,
"Stormin Mormon" wrote:

I had a problem with my AC units. I thought it was the
freon which
was too low.

CY: yeah, everyone says that.



Chris, finding a working newsreader and learning how to use it isn't
difficult. Since you're a regular here, why not take the plunge? After
you've gone cold turkey on top-posting, you could figure out how quoting
is supposed to work.
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Deodiaus wrote:
I had a problem with my AC units. I thought it was the freon which
was too low.
The AC guy came out and said that he first recommended cleaning the
outside AC units, at $80/unit. His partner says that my units look
clean. He says that they should be cleaned every year.
So he takes off the top casing, washes it with a lawn hose, sprays on
an A/C cleaner (sodium hydroxide based), and washes it off. $300
later, he says that the freon needs to be added too. Ok, another $150
later the problem is solved. I got the feeling I was hood winked and
robbed.
Two questions.
Is washing and cleaning the units standard practice? Is it even
necessary to do it once a year? On my old house, I haven't cleaned
them in 3 years and never noticed a higher than average bill for not
doing so.
How much efficiency is lost by not cleaning the units? The repair guy
quoted 50%, but I made a smart ass remark like 5%/yr.


We recommend cleaning the outdoor condensing unit once
a year for a straight AC and twice a year for a heat pump.
The evaporator coil, "the cold part inside" should be
checked at the same time and cleaned if necessary. If you
change your filters regularly, you should have no problems
with the evaporator. I always tell customers to turn the
AC off when you are cutting the grass because the dust and
grass clippings will be sucked into the fins clogging them
up. You should keep hedges and landscaping plants away
from the outdoor unit. A lot of folks will pile mulch and
bark around the AC unit and that's a bad idea too. I like
to see a bed of pea gravel or rocks around them and the
grass/weeds pulled from around the units. Air flow, air flow
should be the AC mantra especially in this hot weather.

TDD
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On Jun 28, 9:47*am, Deodiaus wrote:
I had a problem with my AC units. *I thought it was the freon which
was too low.
The AC guy came out and said that he first recommended cleaning the
outside AC units, at $80/unit. *His partner says that my units look
clean. He says that they should be cleaned every year.
So he takes off the top casing, washes it with a lawn hose, sprays on
an A/C cleaner (sodium hydroxide based), and washes it off. *$300
later, he says that the freon needs to be added too. *Ok, another $150
later the problem is solved. *I got the feeling I was hood winked and
robbed.
Two questions.
Is washing and cleaning the units standard practice? *Is it even
necey essary to do it once a year? *On my old house, I haven't cleaned
them in 3 years and never noticed a higher than average bill for not
doing so.
How much efficiency is lost by not cleaning the units? *The repair guyar
quoted 50%, but I made a smart ass remark like 5%/yr.


I dont think you got hoodwinked. He was acting in your best
interest ; yes, the condensor and evaporator DO contribute to
efficiency if they are clean because maximum heat transfer takes place
thereby increasing cooling capacity over dirty coils, decreasing amp
draw due to the compressor not working as hard, making the units
life expectancy theoretically longer, and making your space cool
faster/better dehumidified. Now that you know how to clean the
coils, you can do that yourself each year prior to startup so it
functions at peak performance.


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Default AC repair question

BTW, I have a follow up question.
I am buying a
AO Smith DL1056 1/2 HP Direct Drive Blower Motor
motor, which needs a 10 mF capacitor (according to manufacturer's
specs),
but the AC guy put in a 7.5 mF cap.
Any reasons why he would do that other than that's what he had
available (because he had to make a special run to grainger anyway?
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On Thu, 2 Jul 2009 21:56:48 -0700 (PDT), Deodiaus
wrote:

BTW, I have a follow up question.
I am buying a
AO Smith DL1056 1/2 HP Direct Drive Blower Motor
motor, which needs a 10 mF capacitor (according to manufacturer's
specs),
but the AC guy put in a 7.5 mF cap.
Any reasons why he would do that other than that's what he had
available (because he had to make a special run to grainger anyway?



It will likely work, but it is almost certain he got that because it
was all that was available or because he thought it was the right animal
for the job.
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Default AC repair question

Can't think of any.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Deodiaus" wrote in message
...
BTW, I have a follow up question.
I am buying a
AO Smith DL1056 1/2 HP Direct Drive Blower Motor
motor, which needs a 10 mF capacitor (according to
manufacturer's
specs),
but the AC guy put in a 7.5 mF cap.
Any reasons why he would do that other than that's what he
had
available (because he had to make a special run to grainger
anyway?


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Default AC repair question

The motor I had in there is
http://americanhvacparts.com/Merchan...ode=fasco-luxa
which as you can see here also comes recommended with a 7.5 MFD cap,
but the manufacturer suggests 10 MFD.

God is Dead
-Nietzsche
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Default AC repair question


? "Deodiaus" ?????? ??? ??????
...
The motor I had in there is
http://americanhvacparts.com/Merchan...ode=fasco-luxa
which as you can see here also comes recommended with a 7.5 MFD cap,
but the manufacturer suggests 10 MFD.

That's a much better capacitor than the crap plastic ones we have in EU;_) I
have no idea why they recommend 10 uF, since the website has a link to a GE
7.5 uF, and the electrician put a 7.5 uF.

Gott ist tod.
(your signature in German).
(Pronounced toont).


--
Tzortzakakis Dimitris
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr





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On Jun 28, 3:32*pm, The Daring Dufas
wrote:
Deodiaus wrote:
I had a problem with my AC units. *I thought it was the freon which
was too low.
The AC guy came out and said that he first recommended cleaning the
outside AC units, at $80/unit. *His partner says that my units look
clean. He says that they should be cleaned every year.
So he takes off the top casing, washes it with a lawn hose, sprays on
an A/C cleaner (sodium hydroxide based), and washes it off. *$300
later, he says that the freon needs to be added too. *Ok, another $150
later the problem is solved. *I got the feeling I was hood winked and
robbed.
Two questions.
Is washing and cleaning the units standard practice? *Is it even
necessary to do it once a year? *On my old house, I haven't cleaned
them in 3 years and never noticed a higher than average bill for not
doing so.
How much efficiency is lost by not cleaning the units? *The repair guy
quoted 50%, but I made a smart ass remark like 5%/yr.


We recommend cleaning the outdoor condensing unit once
a year for a straight AC and twice a year for a heat pump.
The evaporator coil, "the cold part inside" should be
checked at the same time and cleaned if necessary. If you
change your filters regularly, you should have no problems
with the evaporator. I always tell customers to turn the
AC off when you are cutting the grass because the dust and
grass clippings will be sucked into the fins clogging them
up. You should keep hedges and landscaping plants away
from the outdoor unit. A lot of folks will pile mulch and
bark around the AC unit and that's a bad idea too. I like
to see a bed of pea gravel or rocks around them and the
grass/weeds pulled from around the units. Air flow, air flow
should be the AC mantra especially in this hot weather.

TDD- Hide quoted text -

- Show quoted text -


Some increase in use of air heat pumps here; noticing that most of
them are now mounted at least a foot above ground and often on some
sort of hard pad, not surrounded by bushes, flowers and other junk
that can shield them.
Also in winter homeowners seem to make make sure snow does not pile up
against them. Since a heat pump is just an AC in reverse and in fact
can be used as AC in summer and is airflow device that makes a lot of
sense.
After all no one (one hopes) would block off the radiator of a motor-
vehicle and then complain it wasn't cooling the engine properly!
Here in our windy climate that blows dust, autumn leaves etc. around
it would also makes sense to clean outside coils regularly.
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Default AC repair question

The other issue came up when I was looking at the new motor.
The one I had was a one speed motor.
The new one is 3 speed.
Ok, which speed should I choose?
High, med, or low?
I guess a high speed will give you more circulation, but consume more
electricity.
Any estimates on how much this will affect my energy consumption?
Should I just punt and chose medium speed?
--
God is Dead
and I know German!
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"Deodiaus" wrote in message
...
The other issue came up when I was looking at the new motor.
The one I had was a one speed motor.
The new one is 3 speed.
Ok, which speed should I choose?
High, med, or low?
I guess a high speed will give you more circulation, but consume more
electricity.
Any estimates on how much this will affect my energy consumption?
Should I just punt and chose medium speed?
--



Look at the nameplate on the old motor. The rated speed should be there.
Choose the same (or closest) speed on the new motor and wire it up
accordingly.
Make sure the new motor is wired to turn in the same direction as the old
motor. The capacitor hookup will determine the direction of rotation.
Rotation is always specified when looking at the shaft end of the motor.
Energy consumption will be modestly different on different brand motors, but
the difference will probably be negligible if the HP rating is the same,
regardless of the speed.

Cheers
Dave M.


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Default AC repair question

Bull ****!

motor. The capacitor hookup will determine the direction of rotation.


If it is a reversible type motor, there will be 2 wires to change.

Rotation is always specified when looking at the shaft end of the motor.


Again Bull ****. Have you ever looked in a motor catalog and wondered what
they mean when it says CCW Lead End?

Don't make statements not true that can cost somebody aggravation or money.

Stupid Rookie


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On Fri, 3 Jul 2009 21:20:17 -0500, "Big Bob" wrote:

Bull ****!

motor. The capacitor hookup will determine the direction of rotation.


If it is a reversible type motor, there will be 2 wires to change.

Rotation is always specified when looking at the shaft end of the motor.


Again Bull ****. Have you ever looked in a motor catalog and wondered what
they mean when it says CCW Lead End?


Care to post a reference to a catalog page that says that?


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Default AC repair question

Talking to a friend who is an electrician, he told me that maybe just
the capacitor might be of the wrong capacitance.
The problem with buying one off the shelf is that its tolerance might
be off enough to throw the engine off.
Does anyone know how to calculate the torque for an engine with a
capacitance?
I use to know this 30 years ago, but now, don't even know how to
google this question properly!!
Using a 7.5 MFD cap did not work. I tried a 10 MFD cap, which worked
for 10 mins.
BTW, I found a cheap motor at
https://www.plumbersstock.com/produc...rtNumber=12476
Does anyone have experience with this brand,
PARTNERS CHOICE ??

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On Sat, 4 Jul 2009 21:13:41 -0700 (PDT), Deodiaus
wrote:

tolerance might
be off enough to throw the engine off.



They are called motors. Your credibility has taken a dive.
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It sounds as though you are in over your head, and it's time to get a
qualified, experienced person to take over the job.

A residential air system blower motor should work about the same with a
properly rated AC capacitor of 7.5uF or 10uF value (for a motor that's
marked for either a 7.5uF or a 10uF), with only a small difference in motor
speed.
These motors are typically PSC permanent split capacitor type motors, and
may be reversible, but may be designed to operate more efficiently/cooler in
one direction.

The motor you referred to is not a cheap motor, it's just not an exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for about
$30 or less, plus shipping.

--
Cheers,
WB
..............


"Deodiaus" wrote in message
...
Talking to a friend who is an electrician, he told me that maybe just
the capacitor might be of the wrong capacitance.
The problem with buying one off the shelf is that its tolerance might
be off enough to throw the engine off.
Does anyone know how to calculate the torque for an engine with a
capacitance?
I use to know this 30 years ago, but now, don't even know how to
google this question properly!!
Using a 7.5 MFD cap did not work. I tried a 10 MFD cap, which worked
for 10 mins.
BTW, I found a cheap motor at
https://www.plumbersstock.com/produc...rtNumber=12476
Does anyone have experience with this brand,
PARTNERS CHOICE ??


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Actually, where do I find a site with the physics of starter windings
on motors explained. 30 years ago, I had someone explain this to me
in a class, but I have forgotten it all.
Any good descriptive web sites??

BTW, does anyone know of cheaper motors on the web?
https://www.plumbersstock.com/produc...rtNumber=12476
The above site lists some substitute motors, but some just hang my
browser .
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Actually, this is a good intro discussion.
http://www.tpub.com/content/neets/14...s/14177_96.htm

The motor did not rotate when I put in a 7.5 MFD cap. It worked for
about 10 mins for a 10 MFD capacitor.
It was making a squeaking sound, before it cut out. I am trying to
figure out if it is a simple repair in the starter winding and return
the motor, or if I need to replace the motor.

BTW, I look at this as a learning experience. So, unless I fry myself
or the house, nothing is lost.
I have messed up things in my life, but I think I have fixed many a
things too.

I know the difference between an engine and motor. An engine turns
mechanical energy into electricity. A motor turns electrical energy
into mechanical. You can usually run one in reverse to get the
behavior of the other.


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Default AC repair question

The capacitor in this discussion is a Run capacitor, not a start capacitor.
Your progression to this point has been backwards.

When the motor hums instead of starting, it's not because the value needs to
be 8.645789uF, it's because the motor is not wired properly.

You need a qualified, experienced person to take care of the installation.

--
Cheers,
WB
..............


"Deodiaus" wrote in message
...
Actually, where do I find a site with the physics of starter windings
on motors explained. 30 years ago, I had someone explain this to me
in a class, but I have forgotten it all.
Any good descriptive web sites??

BTW, does anyone know of cheaper motors on the web?
https://www.plumbersstock.com/produc...rtNumber=12476
The above site lists some substitute motors, but some just hang my
browser .


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On Sun, 5 Jul 2009 12:58:44 -0700 (PDT), Deodiaus
wrote:

30 years ago, I had someone explain this to me
in a class, but I have forgotten it all.



Obviously you forgot a lot. You referred to an electrical motor as an
"engine".
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Any guesses as to what is wrong with the winding?
Someone suggested looking at the bearings. What do I look for,
excessive wear?
My electrician friend recommended just replacing the motor rather than
trying to diagnose it farther than that.
However, my time is worth about $5/hr, so if I can repair it in less
than I day, I have come out ahead.
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Wild_Bill wrote:
It sounds as though you are in over your head, and it's time to get a
qualified, experienced person to take over the job.

A residential air system blower motor should work about the same with a
properly rated AC capacitor of 7.5uF or 10uF value (for a motor that's
marked for either a 7.5uF or a 10uF), with only a small difference in
motor speed.

snip

why would the speed change?
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Deodiaus wrote:
Talking to a friend who is an electrician, he told me that maybe just
the capacitor might be of the wrong capacitance.
The problem with buying one off the shelf is that its tolerance might
be off enough to throw the engine off.
Does anyone know how to calculate the torque for an engine with a
capacitance?
I use to know this 30 years ago, but now, don't even know how to
google this question properly!!
Using a 7.5 MFD cap did not work. I tried a 10 MFD cap, which worked
for 10 mins.
BTW, I found a cheap motor at
https://www.plumbersstock.com/produc...rtNumber=12476
Does anyone have experience with this brand,
PARTNERS CHOICE ??

Hmmm,
You and your frieed lectrician better learn what is the function of
capacitor for the motor first. If same value is not available always
replace it with next higher value. Same with W.V. You do the math to see
why it is so.


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I found one for $65 shipped at:
http://boatandrvaccessories.com/43587.htm

Does anyone know where I can buy one for $30?

ps1. I am interested in the start capacitance, (the motor makes the
humming sound trying to start up).
ps2. my friend the electrician is not the same as the AC repairman
and not the same as the earlier guy who put in the 7.5 MFD cap (which
seems to be the one that the sites sell with it [A.O. Smith recommends
10 MFD]).
ps3. The reason I was looking for the calculations is that I can see
how sensitive they are to a change in capacitors.

The motor you referred to is not a cheap motor, it's just not an exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for about
$30 or less, plus shipping.

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Deodiaus wrote:
I found one for $65 shipped at:
http://boatandrvaccessories.com/43587.htm

Does anyone know where I can buy one for $30?

ps1. I am interested in the start capacitance, (the motor makes the
humming sound trying to start up).
ps2. my friend the electrician is not the same as the AC repairman
and not the same as the earlier guy who put in the 7.5 MFD cap (which
seems to be the one that the sites sell with it [A.O. Smith recommends
10 MFD]).
ps3. The reason I was looking for the calculations is that I can see
how sensitive they are to a change in capacitors.

The motor you referred to is not a cheap motor, it's just not an exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for about
$30 or less, plus shipping.



I can walk in to several places here in town
and buy one for less. $60 plus $15 shipping?
Kinda runs the price up.

TDD
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Speed changes in PSC motors when the value of the capacitor is changed. Not
a major speed change for the previously discussed values of 7.5uF to 10uF.

For the theoretical explanations, try a book with a detailed section on
Permanent Split Capacitor (PSC) type AC motors.
These motors have been used for deades and are still presently utilized in
many applications from fans and blowers to fractional HP gearhead motors.

PSC type motors differ greatly from split-phase capacitor start motors.

--
Cheers,
WB
..............


"cjt" wrote in message
...
Wild_Bill wrote:
It sounds as though you are in over your head, and it's time to get a
qualified, experienced person to take over the job.

A residential air system blower motor should work about the same with a
properly rated AC capacitor of 7.5uF or 10uF value (for a motor that's
marked for either a 7.5uF or a 10uF), with only a small difference in
motor speed.

snip

why would the speed change?


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"Deodiaus" wrote in message
...
I found one for $65 shipped at:
http://boatandrvaccessories.com/43587.htm

Does anyone know where I can buy one for $30?

ps1. I am interested in the start capacitance, (the motor makes the
humming sound trying to start up).
ps2. my friend the electrician is not the same as the AC repairman
and not the same as the earlier guy who put in the 7.5 MFD cap (which
seems to be the one that the sites sell with it [A.O. Smith recommends
10 MFD]).
ps3. The reason I was looking for the calculations is that I can see
how sensitive they are to a change in capacitors.

The motor you referred to is not a cheap motor, it's just not an
exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for
about
$30 or less, plus shipping.


If the capacitor was a starting capacitor it won't make any difference in
speed, as it is only use to start the motor rotating, and is disconnected
once it is spinning near operating speed. The motor windings will determine
the speed and torque while running.

Most AC blower motors use a running capacitor that stays active while the
motor runs. A running capacitor shifts the Alternating Current sine-wave
between the windings to give the motor torque. A larger value capacitor
will give more torque, and perhaps a little more speed. Induction motors
are greatly affected by the load upon them. If the load is less than the
maximum, a smaller capacitor value is used to keep the rotation speed within
reasonable parameters. An induction motor run without any load will run too
fast and the windings will overheat and break down the lacquer insulation
causing an internal short.

If the motor just hums and does not rotate - there is something else wrong.
A failed capacitor results in this same symptom and is the easiest solution
to try, hence the reason it was replaced. Even a 4F or 5F capacitor
should turn the motor. Check the bearings by rotating the unloaded motor
shaft - it should rotate fairly easily. Usually sealed ball bearing sets
are used in these motors, pressed onto the shaft - replacement will require
a bearing puller.

If the blower is directly attached to the shaft, the only bearings to check
are in the motor. If it is a belt driven set-up (older), the bearings on
the squirrel cage will be suspect.

If the motor spins freely, but still only hums on start up, either a bad
connection to the capacitor (or other component) or a short or break in the
motor windings, not to mention another capacitor failure. These motors tend
to have very fine and compact winding wraps and then take a lacquer bath,
making service difficult if not impossible. If there is a short in the
motor, the first place to check is the bundle where the insulated wires are
soldered to the winding wires, if that is the connection method.

Scott


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Default AC repair question

Anon wrote:
"Deodiaus" wrote in message
...
I found one for $65 shipped at:
http://boatandrvaccessories.com/43587.htm

Does anyone know where I can buy one for $30?

ps1. I am interested in the start capacitance, (the motor makes the
humming sound trying to start up).
ps2. my friend the electrician is not the same as the AC repairman
and not the same as the earlier guy who put in the 7.5 MFD cap (which
seems to be the one that the sites sell with it [A.O. Smith recommends
10 MFD]).
ps3. The reason I was looking for the calculations is that I can see
how sensitive they are to a change in capacitors.

The motor you referred to is not a cheap motor, it's just not an
exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for
about
$30 or less, plus shipping.

snip

Induction motors
are greatly affected by the load upon them. If the load is less than the
maximum, a smaller capacitor value is used to keep the rotation speed within
reasonable parameters. An induction motor run without any load will run too
fast and the windings will overheat and break down the lacquer insulation
causing an internal short.


Not even close. Induction motor speeds vary little from no-load to
full-load (slip from no-load to full-load of typical induction motor
[not some ceiling fan junk] is 1 to 3 % of synchronous speed). Running
completely unloaded is perfectly fine and the windings of an induction
motor will *not* overheat in that situation. (hint, the motor draws less
current when it's unloaded)

If the motor just hums and does not rotate - there is something else wrong.
A failed capacitor results in this same symptom and is the easiest solution
to try, hence the reason it was replaced. Even a 4F or 5F capacitor
should turn the motor. Check the bearings by rotating the unloaded motor
shaft - it should rotate fairly easily. Usually sealed ball bearing sets
are used in these motors, pressed onto the shaft - replacement will require
a bearing puller.

If the blower is directly attached to the shaft, the only bearings to check
are in the motor. If it is a belt driven set-up (older), the bearings on
the squirrel cage will be suspect.

If the motor spins freely, but still only hums on start up, either a bad
connection to the capacitor (or other component) or a short or break in the
motor windings, not to mention another capacitor failure. These motors tend
to have very fine and compact winding wraps and then take a lacquer bath,
making service difficult if not impossible. If there is a short in the
motor, the first place to check is the bundle where the insulated wires are
soldered to the winding wires, if that is the connection method.


These are good troubleshooting points. But your statement earlier about
motor speed/load is off.

daestrom


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Posts: 39
Default AC repair question

Deodiaus wrote:
Any guesses as to what is wrong with the winding?
Someone suggested looking at the bearings. What do I look for,
excessive wear?


Well it's possible that this is still the original problem and the
capacitor was not bad to begin with.

The symptoms point to something in one of the two winding circuits.
There are two separate windings in a single phase induction motor. In
many motors one of the windings is only energized during starting and
then turned off by a centrifugal switch. But this thread has been
talking about capacitive run type (and that's common for blower motors)
so we can ignore problems with the switch.

If the two windings are energized from the same power source without any
capacitor at all, then no torque is developed and the motor sits and
hums. So one thing is it may be wired up wrong. Recheck your work
against the circuit diagram (often inside the panel or in a manual).

If the bearings or blower are seized up, the motor can't develop enough
torque to start spinning. Or you may get it started but the load is so
great that it overheats and shuts down. I think you mentioned it ran
for a while one time? When everything is turned off, you should be able
to easily turn the thing by hand, blower and all.

If one of the two windings has developed an open, then the other winding
alone can't develop torque to start and it will just hum. This *may* be
just an open in a connecting wire and would be easy to fix. But if it's
down inside the winding, rewinding a motor is quite a task and often not
worth the effort.

If your handy with an ohm-meter you can check for opens easy enough.
Just lift the leads and read between them. Be sure to turn off the
power though, ohm-meters tend to smoke when connected to live AC power.

daestrom
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Posts: 5
Default AC repair question


"daestrom" wrote in message
...
Anon wrote:
"Deodiaus" wrote in message
...
I found one for $65 shipped at:
http://boatandrvaccessories.com/43587.htm

Does anyone know where I can buy one for $30?

ps1. I am interested in the start capacitance, (the motor makes the
humming sound trying to start up).
ps2. my friend the electrician is not the same as the AC repairman
and not the same as the earlier guy who put in the 7.5 MFD cap (which
seems to be the one that the sites sell with it [A.O. Smith recommends
10 MFD]).
ps3. The reason I was looking for the calculations is that I can see
how sensitive they are to a change in capacitors.

The motor you referred to is not a cheap motor, it's just not an
exessively
inflated priced motor.
New surplus blower motors can be found at numerous surplus dealers for
about
$30 or less, plus shipping.

snip

Induction motors are greatly affected by the load upon them. If the load
is less than the maximum, a smaller capacitor value is used to keep the
rotation speed within reasonable parameters. An induction motor run
without any load will run too fast and the windings will overheat and
break down the lacquer insulation causing an internal short.


Not even close. Induction motor speeds vary little from no-load to
full-load (slip from no-load to full-load of typical induction motor [not
some ceiling fan junk] is 1 to 3 % of synchronous speed). Running
completely unloaded is perfectly fine and the windings of an induction
motor will *not* overheat in that situation. (hint, the motor draws less
current when it's unloaded)


Ah, I should have qualified that with "low-torque/low speed" induction
motors (less than 300 RPM) often found in smaller squirrel cage blower fans
and in some ceiling fans. I have not worked on many high torque, high speed
induction motors to consider them typical of induction motors. Low torque
motors are designed to carry a specified load and can run up to 25% faster
without that load. But I concede, a blower motor requiring a 10F running
capacitor probably is a high torque induction motor that will not suffer
from heat-rise unless it is from the bearings.


If the motor just hums and does not rotate - there is something else
wrong. A failed capacitor results in this same symptom and is the easiest
solution to try, hence the reason it was replaced. Even a 4F or 5F
capacitor should turn the motor. Check the bearings by rotating the
unloaded motor shaft - it should rotate fairly easily. Usually sealed
ball bearing sets are used in these motors, pressed onto the shaft -
replacement will require a bearing puller.

If the blower is directly attached to the shaft, the only bearings to
check are in the motor. If it is a belt driven set-up (older), the
bearings on the squirrel cage will be suspect.

If the motor spins freely, but still only hums on start up, either a bad
connection to the capacitor (or other component) or a short or break in
the motor windings, not to mention another capacitor failure. These
motors tend to have very fine and compact winding wraps and then take a
lacquer bath, making service difficult if not impossible. If there is a
short in the motor, the first place to check is the bundle where the
insulated wires are soldered to the winding wires, if that is the
connection method.


These are good troubleshooting points. But your statement earlier about
motor speed/load is off.

daestrom



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