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Wrong size capacitor installed. Advice?

Posted by homeagain (My Page) on
Wed, Apr 29, 09 at 15:50

We hired this company in March to repair our heat pump, which wasn't working. They replaced the capacitor. The unit stopped working again last week. I called the number listed for them for several days, with no answer. After some research I have found that they have since gone out of business.
I called another company to come and repair the unit. The unit is a Ruud and has a reset button. The repair guy pushed the reset button waited 15-20 minutes to see if it was cooling, then left. About an hour later I noticed it wasn't getting any cooler, went outside and the unit had stopped working again. I pressed the reset and it started up. Same thing a little while later. I called the company back told them what was happening and the guy came out again.
He found that the old company had replaced the capacitor with a new capacitor in the wrong size. A 5 instead of a 3?? This new capacitor was causing the motor to work too hard, overheat and shut down. The guy from the new company replaced the capacitor with the correct size and the unit seemed to work, however was making a "rattling" sound. The repair guy stated that the bearings may have gone bad as a result of the wrong capacitor and I should probably try to get a hold of the old company and make them fix it.
About an hour after he left, it stopped again. However, this time when I press restart, it "makes noise" but the fan doesn't spin. So after all this, the unit still isn't working.

When I do a google search of the old company, there is a direct link to a large contractor here in the area that the hvac company was affiliated with. I've called them twice and emailed the president of the company, but no response.

I'm also ambivalent about the work done by the second guy. We paid for a service call but the unit still doesn't work. What exactly does the diagnostic fee of $135 cover?

Thanks for your help!!!


Follow-Up Postings:

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RE: Wrong size capacitor installed. Advice?

There are any number of things that could be causing your problem. It's really not a good idea to diagnose an airconditioning problem without actually doing the diagnostics personally. It is only what we call the SWAG method (service with a guess). I will do my best guess based on the most common problem I have seen through the years, hoping to give you some insight.

Most residential condenser fan motors use from a 3 to a 10 mfd run capacitors..depending on how much work it has to do and it's horsepower (or fractional horsepower) rating. I doubt if the 5mfd capacitor would burn the fan bearings. If you are being told precisely that, it is inaccurate. Are you even sure it is the fan? If it is the fan, it has an internal overload that would cause the fan to quit running if it overheats, causing head pressure to build and the high pressure switch to trip, shutting down the unit. My most common experience with the RUUD's with the reset buttons you refer to, is that it is a low pressure cut out. If the refrigerant charge is too low and the unit runs for a while, the pressures drops below the calibrated pressure rating and shuts the unit off before damage to the compressor is done. If you went right out, when the unit shut off and tried the reset and nothing came on, I suspect (without being there) the refrigerant charge hadn't equalized and was too low. You will need to be more observant of what's happening. Does the fan shut off and then eventually the whole unit? Or does the whole unit just Suddenly shut down? Is the "ratteling" caused by vibration or is there a mechanical fault?

As for the costs, a diagnostic fee of any charge should cover the service charge and time and effort required to properly diagnose the problem(s). Is this the only charge on the bill? What about the capacitor?...I'll just point out that for a technician to show up, there are costs to the company....Technician Wages, Workman's Comp, Social Security, Liability Insurance, Benefits, Vehicle Insurance, Vehicle Maintenance, Fuel, Tags, Vehicle registration, business license fees, taxes, tools, building rent, utilities, property taxes and insurance, certification fees, continuing education, parts and supplies. There are others but I think you get the idea....

These are 24/7 costs and a portion is passed on to you for that hour or any portion of it. Then the company has to show a profit or Uncle Sam will not consider it a business. So To show a profit and pay operating costs, you might see there's not much left!!! But to put it into perspective, it wouldn't be prudent of me or others to dispute the charges. They are what they are as long as you get what you paid for.

That doesn't by any means diminish the fact that you should get what you are paying for. I don't know the details on the bill but if they listed them as Diagnostic and Repair and then list the capacitor in addition, then yes, you should get them right back out. In the future, any time you get a bill....for anything....get it fully itemized.


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RE: Wrong size capacitor installed. Advice?

A larger capacitor does not cause "the motor to work too hard, overheat and shut down."

Something else is wrong.

A 'hard start' kit is just another capacitor and a time delay relay.
The extra capacitance allows the motor to come up to speed faster and reduces power dissipation.

The manufacturer puts in the smallest capacitor they can since it is a rather expensive component in the overall scheme of things.


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RE: Wrong size capacitor installed. Advice?

I'll try to clear things up as much as I can.

"This new capacitor was causing the motor to work too hard, overheat and shut down". This is what the new repair guy told me was the reason for the problem. Although the thermostat continued to flash that it was working and the unit in the attic continued to run, the unit outside had stopped. Pressing the re-set button on the unit outside would cause it to start back up, the temperature would drop .5 degree on the thermostat and the next time I checked the unit outside would have shut off again.

So, I had hoped to get the first company back out to fix the unit at no additional charge since it was their error in putting in the too large capacitor (according to new guy) that was causing the problem.

You guys are saying that's not the case, so now I've paid this new company a "diagnostic fee" and their diagnosis is wrong and I still don't have a working unit.

As for replacing the capacitor with the correct sized one, new repair guy did not charge for that because he had missed the problem the first time, when he simply pressed the reset button and left. Since the wrong capacitor in the unit was only a few weeks old he took that as "trade" for the new one.


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Advice on a/c unit

Sorry, I didn't answer all the questions.

"You will need to be more observant of what's happening. Does the fan shut off and then eventually the whole unit? Or does the whole unit just Suddenly shut down? Is the "ratteling" caused by vibration or is there a mechanical fault?"

The fan on the outside unit doesn't spin at all since about an hour after he replaced the capacitor. The unit in the attic runs, the outside unit runs but the fan blades on top on the unit doesn't spin and the house doesn't get any cooler. There wasn't a rattling sound until he replaced the capacitor, when I came outside and he showed me the wrong one and the paper on the inside of the unit stating which size should be used the unit was running nosily. When I asked why it was so noisy he then stated the stuff about the bearings may have been burned up.

I called again after it quit working and he told me that his best guess is the too large capacitor damaged the motor and I should really contact the other company. So he essentially took no responsibility for it not working after he left.

Bren ( can you tell by all my technical jargon that I'm a girl?)


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RE: Wrong size capacitor installed. Advice?

Ok, if I have it straight, the outside condensing unit is running but the fan isn't after it's run for a while and the house temp. has dropped a few degrees. My guess is, the fan motor may be shot but....the capacitor wasn't the cause. I think the first guy thought it was the capacitor and that's why he changed it out. The second guy did the same thing. Neither ran any diagnostics to see what the problem was. Everything points to the fan motor needing replacement. Now again, without running diagnostics (mainly an amperage reading from start-up to kick-out and resistance readings of the motor windings and checks for short to ground, etc.) in person, this is only a guess. There could be a few other problems but chances are, it's the motor..

Just some brief rundown...The motor bearings on that motor are not ball bearings, they are what is referred to as race bearings. A layer of oil is what allows it to turn freely. If the motor needs oiling, it may start drawing increased amps, get hot and trip out on overload. It doesn't take too much running without oil to ruin the race. Usually, you get a lot of squealing from the motor when this happens.If it did this too many times, the insulation on the windings could have been compromised and the motor is just shot. Also, if the motor trips out too many times, the internal overload weakens, tripping the motor too soon. In that case, the motor needs to be replaced since the overload is not serviceable.

So I say again, if anyone is telling you the 5 mfd capacitor burned out the motor, this is inaccurate. I think the second guy, knowing the capacitor had just recently been replaced, should have checked the motor to see if there was a problem. The first guy should have checked the existing capacitor if he thought that was the problem. Everyone is in a hurry, not enough time to do it right the first time but plenty of time to keep coming back. Tell the second guy that it doesn't matter who did what, you paid him to diagnose the problem and he didn't do it, come back, diagnose (don't guess) and tell you what is really wrong. Have him put it in writing. Get it fixed and if his diagnosis wasn't the problem, undo what he just did, un-charge you for the bad diagnostics and diagnose again. If he can't find the problem, then he shouldn't be charging you and you should call someone else.


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RE: Wrong size capacitor installed. Advice?

Larger than required capacitors will not overload a start winding in a compressor or fan motor.

The smallest capacitor that will allow reliable starting is selected to save $$.
High voltage motor start and run caps are not exactly cheap.

I worked verifying the sizing of motor caps for a couple years working on my engineering degrees.

All the capacitor is doing is providing phase shift so the single phase induction motor has a starting torque.
More phase shift will not harm the start winding, but will increase the starting torque the motor can produce.

A 'hard start kit' for a compressor is just another capacitor and a time delay relay to make sure it comes out of the circuit without relying on the start winding centrifugal switch.

Needless to say, hard start kits do not damage start windings, and are supplied by the manufacturers as part of some condensers since a single size compressor motor can be used in a range of units with different capacities with different starting requirements.

The fan motor in the condenser is just another single phase motor that needs starting torque.
Notice how the standard test is to spin the blade and see if the motor than comes up to speed?
You are supplying the starting torque.


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RE: Wrong size capacitor installed. Advice?

We all have to agree, the statement from the OP's tech that says the larger capacitor caused the bearings to burn out is absolutely incorrect. He could have added a 25mfd capacitor and that would not have made the bearings go bad.


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RE: Wrong size capacitor installed. Advice?

It is primarily the start winding that can be overheated breaking down the winding's insulation.

Of course, we know we wouldn't put a 25mfd run cap on a PSC-motor that calls for a 3mfd cap.

The PSC-motor is not engineered to function properly with that much of a phase shift.

I used a capacitor tester & replaced capacitors that were below their rating.

I do not like to cause hard feelings, therefore I am not going to say any of you are wrong. - udarrell

Here is a link that might be useful: Sizing Equipment


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RE: Wrong size capacitor installed. Advice?

udarrel...I was not saying it is ok to use a 25mfd. You could put a 50 mfd in there and it would not burn out THE BEARINGS. The poster is being told the larger mfd burned out the BEARINGS. Start winding, run winding, schmuck winding....a capacitor of any size, large or small will not burn out BEARINGS.


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RE: Wrong size capacitor installed. Advice?

you would have to really crew up the value of a run cap to have any affect.

Ever notice the tolerances on them?
+100% is not unheard of.
That is double the 'rated' value.


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RE: Wrong size capacitor installed. Advice?

So it is everyone's opinion that the first guy didn't do anything wrong by replacing the capacitor with a larger size. He either diagnosed incorrectly or there was another underlying problem that he didn't catch, which showed itself a month later?

The second guy, basically blamed any problems on the first guy, to get out of doing anything more than he had already done. Which was press the reset button and replace the capacitor. And yes, his final suggestion was to get a hold of the first company because the larger capacitor probably burned up the bearings.

I finally got a call back from the contractor who was connected to the first guy who went out of business. He also said the same thing about the capacitor not causing the problem but agreed to put me in touch with the first guy.

I finally talked to the first guy today, who said the 2nd guy didn't know what he was talking about but that he would come out and take a look tomorrow.

The unit is 3 years old and under a 10 year warranty for parts.

So is it the general concensus based on what little info I was able to provide that the fan motor needs replaced?


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RE: Wrong size capacitor installed. Advice?

My SWAG (service with a guess) is the fan motor needs to be replaced. The motor itself may be ok but the thermal overload may be defective. The overload is internal and cannot be serviced so the motor would have to be replaced in that situation also.

jonathan...There are a number of factors that can cause a motor to overheat. Without more information, it's difficult to say what is overheating your motor. To answer your question directly though, yes, a too small mfd capacitor can cause your motor to overheat.


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RE: Wrong size capacitor installed. Advice?

I am a service manager in Atlanta. I have wondered this very question and have put it to the test. We would miswire dual caps for training purpose, put the fan on herm and herm on fan with a variety of sizes, and what we found was that after 30 min or so the condenser fan would overheat and shut down. We also tried this with replacing a 3mfd with a 5mfd and the same thing happened it just took longer, a month in one case. I would not recommend doing this unless it was temporary and gave you time to get the correct size. We keep 3mfd caps on the shelf just for Rheem and Ruud for this very reason!


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RE: Wrong size capacitor installed. Advice?

gking, I'm with you on this.

The problem with substituting higher than spec caps is that the mfr has determined the best size for the application.
The start windings will undergo an increased current for larger than spec causing long term heat deterioration of the start winding.
The claim that when the mfr says 3mf because 5mf is more expensive is hogwash. Using the higher value cap will cause a long term longevity issue.

So, if you can't find the spec cap, you could TEMPORARILY
use the higher value, but should replace it ASAP .


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RE: Wrong size capacitor installed. Advice?

The value of the capacitor (or a run cap) has no affect on the current in the circuit.

It is there to produce phase shift, and more phases shift produces more torque.

For a run cap this may alter the speed of the motor slightly, and thus the fan load on the motor.

THIS could overload the motor.


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