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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r
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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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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Deodiaus wrote:

Probably what he had on hand. The effect depends on the type of motor, in some cases the capacitor is there just for power factor correction, and in others it creates a phase shift for one of the two windings. In the latter case, a lower value capacitor will result in slightly less horsepower.
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In all liklihood, depending upon the motor, the capacitor is just used for startup. The result will be less starting torque. For a blower, the starting torque requirements are minimal. For a compressor, however, considerable starting torque may be necessary.
Without a capacitor, there is no starting torque. The motor will run in whichever direction it is started if that were possible,
Bill
--
Private Profit; Public Poop! Avoid collateral windfall!

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Salmon Egg wrote:

I've never seen a capacitor start motor used with a blower, they're for applications like air compressors that require high starting torque, which a blower does not.
What I have seen are shaded pole and PSC motors, generally 1/4HP and smaller are shaded pole, while larger or higher quality are PSC. The capacitor on a shaded pole motor is just for power factor correction, while that for a PSC motor creates the phase shift.
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The motor I had in there is http://americanhvacparts.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MOT2426003&Category_Code sco-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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http://americanhvacparts.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MOT2426003&Category_Code sco-luxa
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).
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Tzortzakakis Dimitris
major in electrical engineering
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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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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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On a multispeed motor the rated horsepower will only be at the maximum speed. The lower speeds will be less horsepower with correspondingly less electrical consumption. If you replace a 1/2HP single speed motor with a 1/2HP 3 speed motor, the highest speed of the 3 speed motor will be the same as the only speed offered by the single speed motor. That is assuming of course that both motors have the same number of poles, which you want to be the case if you are replacing one with the other.
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Bull Shit!

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

Again Bull shit. 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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Care to post a reference to a catalog page that says that?
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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/product.html?partNumber 476 Does anyone have experience with this brand, PARTNERS CHOICE ??
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wrote:

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 .............

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Wild_Bill wrote:

It sounds like he already did. He's just double checking the work done since he noticed the capacitor that was installed is not the value that was listed.
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Wild_Bill wrote:

<snip>
why would the speed change?
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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 .............

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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.

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