Electric motor start-run capacitor FAQs:

Questions & answers about choosing, installing, & troubleshooting starting capacitors & run capacitors used on electric motors.

This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment. These electric motors use a capacitor to start and run the motor efficiently.

Electric Motor Starting Capacitor or Run Capacitor FAQs

These electric motor start or run capacitor questions & answers were posted originally

at CAPACITOR TYPES, for MOTORS - be sure to review that article.

Also see CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS.

Capacitors are electric devices that get an electric motor running at start-up by providing a "jolt" of stored electrical energy, or that help keep a motor spinning once it has started.

The starting capacitor helps a motor start spinning by creating a high-torque, rotating, electrical field in the motor.

If either or both start and run capacitors are defective the motor may try to start but will hum and won't keep running. You may hear a compressor or fan motor humming or observe that it's getting hot.

On 2018-06-16 by Dan Jacobson

What does the "VC 12/13" of
Metallized Polypropylene Capacitor

YUHCHANG 30uF 250VAC MPP VC 12/13
mean?

On 2012-06-02 by John - AC Motor has three wires, white black and orange. 22Ufd cap has four terminals and rectangular.

AC Motor has three wires, white black and orange. 22Ufd cap has four terminals and rectangular.

The two terminals on each end (left or right end) are shorted together. Put black line and black motor on one end and white neutral and white motor on the other end and motor humms and runds when I manually spin it.

Where do I put the orange wire from the motor? When AC is on like mentioned above I get 140 VAC from orange to ground, 199 VAC from orange to neutral and 160 VAC from Orange to black. This is for a pool pump from Intex with the salt chlorinator on it.

On 2012-05-08 by Alex

My window AC unit goes through cycle of 45 seconds compressor ON, 3 min compressor OFF.
Is this capacitor issue? What is the best approach to troubleshoot this problem?

Answer: Start at COMPRESSOR / CONDENSER DIAGNOSTICS

On 2012-05-07 by (mod) -

Thanks for the note, Rob. It was helpful.

On 2012-05-07 by (mod) - can you substute a larger voltage capacitor with the same mfd ?

Yes, if the uF rating is the same, using a capacitor that could tolerate higher voltage than that to which it would be subjected is not harmful.

Use of a capacitor at voltages below its rating will do no harm.

Run capacitors must not be subject to voltages exceeding 10 percent of the nominal rating, and start capacitors must not be subjected to voltages exceeding 30 percent of the nominal rating.

Watch out: The voltage to which a capacitor is subjected is not line voltage, but is a much higher potential (often called back electromotive force or back EMF) which is generated in the start winding. - Copeland Electrical Handbook

On 2012-05-07 by Anonymous

can you substute a larger voltage capacitor with the same mfd ?

On 2012-05-04 by Rob - If I switched the two leads from their original position, would that make my blower run backwards?

David, No.

Not all motors are even reversible...but capacitor leads are for a run side and common side.

If one wire to capacitor is brown/white and the other is brown.....the motor repair shop says it doesn't matter nowadays.....but I still put the brown/white on common terminal and brown on run terminal.

On 2012-05-03 by Anonymous

when u first turn unit on,it runs fine and gets, but after 30 to 45 minutes,the fan on unit outside stops turning,quits getting cold

On 2012-05-02 by David

I just replaced the two-lead capacitor that sits on top of my squirrel cage. If I switched the two leads from their original position, would that make my blower run backwards?

On 2012-04-07 by (mod) -ac unit trys to start but stops and gets clicking sound

Tom, we can't be sure what's wrong from just your note, and the problem could be anything from a frozen compressor motor (costly) to a refrigerant or control relay problem (less expensive)

You should find some diagnostic help in the article titled "Air Conditioner Won't Start" under the larger topic "LOST COOLING CAPACITY" - see the links(links found at the ARTICLE INDEX near the end of this page) , and do keep me posted, what you find will help other readers.

On 2012-04-07 by tom

ac unit trys to start but stops and gets clicking sound

On 2012-02-24 by Anonymous

when connecting two motors to the same circuit, such as a compressor and a condenser fan, the two loads must always be connected which way?

On 2012-01-09 by Kash Where can I find ac single phase schematic diagram?

Where can I find ac single phase schematic diagram?

On 2011-11-25 by (mod) - if your A/C unit is not cooling,

Denzil: if your A/C unit is not cooling, that is not producing cool air, then contrary to your description , the unit is not "working as normal" and it needs repair by a trained service tech.

Simply arbitrarily trying to "re-gas" by which I assume you mean adding refrigerant, is not a proper repair and worse, if you overcharge the unit you risk damaging the compressor, leading to a much more costly repair. I'd call a service company and ask for a diagnosis of the unit.

On 2011-11-25 by (mod) - wiring a hard start capacitor

Mark, when wiring a hard start capacitor it is most often wired in parallel to the existing unit.

Your two capacitors are either a Start cap and a Run cap or there was already an additional hard-start capacitor installed. Trace the wires to their respective terminals. Wires to a terminal marked S will be the start unit and marked R will be to the run circuit.

See details at MOTOR CAPACITOR WIRING GUIDE

On 2011-11-25 by (mod) -

Riz and Anon: wiring the blower fan motor to the unit will involve just a few wiring connections - typically from a control board or panel or fan limit switch to the motor.

It would be dangerous to give arbitrary wiring directions for an unknown piece of equipment as there are shock, fire, and electrocution hazards. The wiring requirements should be visible on a label attached to the blower unit or in the unit's installation manual.

On 2011-11-25 by denzil

Airconditioner works as normal but not cooling off the room, when try to regas it will not regas as though it is full, what could the problem be?

On 2011-11-23 by Mark Miller

I have a mini split heat pump/AC unit and it has two capacitors with two terminals each. The two capacitors are actually the same brand and voltage/microfarad rating as the hard start capacitor that I purchased. How do I wire the hard start cap to a two capacitor system? Two capacitors are wired in series using the two inboard terminals

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MOTOR CAPACITOR WIRING GUIDE

On 2011-11-14 by Anonymous

does anyone know how to wire the blower motor to the unit

On 2011-11-14 by riz

im having a hard time getting an answer,i need to know how to install ablower motor.i need the wiring configuration

On 2011-11-02 by (mod) - Whirlpool upright freezer motor capacitor

Nicholas,

I've seen an HVACR tech just take off the PTC relay and shake it - listening for loose debris. If you hear stuff rattling around that device has failed internally and needs replacement or your compressor won't start. (The PTC is a thermal relay that feeds the start capacitor). Some of the newer relays are solid state and while less costly, are more easily burned up by a power surge than older mechanical relays.

If the PTC relay on your freezer seems OK you could try replacing the start/run capacitor. If I were making a trip to the HVACR supplier I'd just buy and replace both parts as a try since they're not expensive and it'd save wasting a trip. It's a bit of a shotgun approach, replacing two parts, but in this case cost-effective.

Beware that if compressor start up problems continue the compressor motor itself could be near end of life.

BEWARE of big shock hazards when messing with capacitors.

Keep us posted - what you find will help other readers.

On 2011-11-02 by Nicolas

I have that Whirlpool upright freezer that I bought a few months ago. The freezer is working most of the time. If there is a quick power failure less than one or two second the freezer will not start again. I can hear every minute a series of click but nothing from the compressor.

If I want the freezer to run again I need to unplug the freezer for a few minutes a plug it back. The freezer is still under warranty and the technician came to my place. The technician told me that a short power failure is hard for a freezer and it is normal that it will not start again.

Could that be the PTC switch that is defective? I have never see that on any other freezer. Cloud that be true that some brands behave that way? Do i need to install a hard-start capacitor?
Thanks!

On 2011-10-13 by (mod) - out side unit fan will not start but when i give it a spin it will run slow

Bill, what you describe may be a motor with a bad start/run capacitor.

On 2011-10-10 by bill

i have a problem with my motor out side unit fan will not start but when i give it a spin it will run slow and the shuts off what do i have to do

On 2011-10-04 by (mod) -

Mich,

You can try replacing the capacitor again, but if the problem is recurring, and as a capacitor should not fail in such a short time,

I suspect you may need to replace the motor.

On 2011-10-04 by mich

hello, I have the exact same problem & symptoms as Curt & I wanted to know if he is still monitoring this post if replacing the fan motor did indeed work. I know my unit is old and I did replace both the contact relay & then the start/run capacitator about a year and a half ago.

I suspect I might still have to change the capacitator again but I would like to be a little more sure if I only need 1 or the other or both before I proceed since the capacitator itself is around $45 and I'm sure the fan is considerably more.

The outside condenser fan stopped during the night last night & we woke up to warm temps & a buzzing unit outside & the fan not operating. A half an hour later I restarted the system & it proceeded fine and cooled down the house back to 77 within 25mins.

But then when it when on to cycle again later it started normally but then during the cycle the fan stopped which then seemed to overheat the system & then the compressor started buzzing again. I shut it down again & it repeats each time the same after everything cools down.

The system cools well while the fan runs but then obviously stops cooling when the fan stops. Also, when the fan is running, even though the compressor is buzzing it is cold at the top of the compressor & hot at the bottom & the intake tube is very cold & the outake tube is very hot.

I notice that when the fan does stop, the area above the fan motor is very hot & I also noticed that if I didn't catch it & turn off the system the moment the fan stopped, it then made the compressor hot it would continue buzzing until I shut the system off.

On 2011-09-25 by bill

lock nut is off but the units are not seperating. are there rings or clips

On 2011-09-07 by (mod) -

Abdon we've illustrated the typical wiring connections for a start/run capacitor in the article above. Your own system might work a bit differently; look for a wiring diagram on labels or in the instruction manual for your device, or at the very least, look at how the original capacitor was wired up for advice.

Typically there are at least 3 connectors: Common (C), Start (S), and Run (R). Or on a pure "start" capacitor with a separate (or absent) "run capacitor" the connections would be (C) and (S).

I don't ususally see the capacitor wired to the input side of the compressor relay - but it might work fine connected to the output side that actually powers the compressor.

Is your system not working after a new capacitor was installed? If so I'd start by asking the service technician for more help.

On 2011-09-06 by abdon

how should the wires go to a capacitor, ac man put the orange wire coming from the compessor on herm of the capacitor and the red wire on the c on the capacitor which connects to the contactor is that right?

On 2011-09-06 by (mod) -

Curt I agree that you'd want to see if it's the compressor that's running so hot, not just the fan motor. But keep in mind that even a small electric motor can get very very hot if it's internal parts/bearings are failing.

An overcharge of refrigerant can damage a compressor and might lead to its failure. Under-charge: usually the compressor keeps chugging away but just never reaches normal operating pressures. There may be a way that this damages the equipment but I don't know it. I'll do further research on that question.

On 2011-09-04 by Curt

Thanks for all Dan. I am not for sure where the heat is coming from but I don't think a fan motor could produce that much heat that fast. But it does bother me that it does not seem to spin as fast as it should. Since everyplace is clased for the next couple of days it's fortunate that it has cooled off outside. One more question, could low freon level cause it to heat up?

On 2011-09-04 by (mod) -

If you mean the fan is getting very hot, the motor sounds as if it's failed. Before going for a costly and complete system replacement I'd want a clear diagnosis of just what's wrong. Hate to replace a whole compressor/condenser if it were just a bad fan motor or control.

If you mean it's the compressor getting very hot, an overheating compressor sounds as if it could be a failing unit; however a clogged condensing coil or thermostatic expansion valve might also produce elevated high side pressures and temperatues. You need an experienced HVAC tech on site.

On 2011-09-03 by Curt

Hi Dan, I have a couple of more pieces to the puzzle. Spraying the unit with water did make the fan start spinning again. But a couple of other observations are:

1. the unit seemed to get really hot and do it fast - the sprayed water almost produced steam. This was after running for only 15 minutes.

2. there is a 3.5 ton unit next to this 3 ton that had been running all day and did not seem that warm.

3. the fan that I am working on is suppose to be 1075 RPM the one on the 3.5 ton is 1100 RPM but I could see that the one I am working on is noticeably slower when it is running.

4. in comparing the feel of the tubing running into the houses from both the A/C units, the cool one felt about the same but the other one was noticeably warmer on the unit I am working on.

Again thank you so much for your help. I am trying to do what I can to get this working. I was told over the phone to replace it would be about $2800 because they would also have to replace stuff in the house.

On 2011-09-03 by Curt

By the way, the fan motor does have Thermo Prot written on the label.

On 2011-09-03 by Curt

Thanks Dan. I have been leaving the unit off except to try these things. I will try the experiment. If cooling it down with water causes the fan to start spinning again then that should confirm that the next step is replacing the motor? Right?

On 2011-09-03 by (mod) -

Curt indeed it sounds as if a fan motor is overheating and shutting down on thermal overload. IT may have an internal thermal reset, that's why its starting up again after cooling off. You can experiment by spraying the compressor/condenser with water to cool things down faster once it has shut down.

Don't keep running the system without the fan - there is risk of damaging the compressor.

On 2011-09-03 by Curt

I left the unit off for a hour and then turned it back on. Fan started up fine but after 10 minutes stopped spinning again. I don't know when the run capacitor kicks in but since I already replaced that, I think I am going to replace the fan motor to see if that fixes it.

Any tricks, concerns, or other advice I should be aware of before replacing it? Thanks...
By the way, I replaced the control board in the furnace about 6 months ago. Don't know if it matters ... just thought I would mention it...

On 2011-09-03 by (mod) -

Uh oh Curt, if the humming is from the compressor it sounds as if it's not starting. But first check the start relay for that component. A control board in your unit may be responsible for starting both compressor and fan unit. Normally they'd both run simultaneously.

On 2011-09-03 by Curt

Thanks Dan. The hum is not coming from the fan motor and spinning the blades did not always work either. It seemed to work only after I had shut off the unit for a while. I have shut it off again to see if it will start spinning again after I turn it on. It does seem to blow out cold air through the vents when running if that matters.

On 2011-09-03 by (mod) -

Thanks for the nice notes, Barrett and Curt. We work hard to try and make our information useful and without bias; reader questions and comments are quite helpful.

Curt:
It's a common diagnostic trick: if a fan motor will get going and keep running when you give the blades a spin, we suspect (and replace) the start/run capacitor. You did that and it seemed to fix things.

Now that remaining hum is worrisome. I'm speculating in the dark, but

- is the hum from a compressor that is having trouble getting going? or from the fan motor? A double fault - two things failing at once - is not what we should first suspect, but in fact one failure can trigger another; a compressor running or that keeps trying to run without the cooling fan in operation might be damaged.

- was the fan motor damaged by it's repeated failed start attempts before you replaced the capacitor?

See if spinning the fan gets it going again - if so the new capacitor failed, was wrong value, or another elecrical problem or wiring problem killed it.

Finally, don't rule out a bad compressor start relay or contactor or control board.

Start with the fan, listen to the compressor, and, sorry to say if it were me, one more try and I'd give up and bring in an experienced HVAC tech.

Keep us posted. What you learn will help others.

On 2011-09-03 by Curt

I agree with Barrett that this site extremely helpful. Thank You.

My issue is that my condenser fan is not working. It spins freely when moved and it has even started working at times if I manually spin it. I replaced both the start and run capacitor and it started right up. But when I checked on it later the fan was no longer spinning but I could still hear the hum from the unit. Any advice. Thanks...

On 2011-08-12 by (mod) -

Barrett: just guessing, but consider this: because the compressor/condenser is designed to be outdoors and thus not harmed by rainfall even if it is running, it shouldn't be the case that spraying the unit with fan running would have shorted something or caused damage.

I suspect that the compressor motor is seizing. You could try replacing the start/run capacitor and see if that gives some added life; an HVAC tech can test the motor itself for seizing, typically doing some electrical tests (amps draw). Keep us posted.

On 2011-08-12 by Barrett

By the way, this site is awesome. Extremely helpful even if I end up having to punt to a tech. Thanks!

On 2011-08-12 by Barrett

I recently had my house painted. Half way through the ac quit working. Noticed the high pressure reset was tripped, I reset the switch on the condenser unit and the fan was up and running. Next morning I came back and I was reset again (not running).

I tripped it and the condensing unit ran again. I had heard to clean the fins with a hose, but didnt know not to have the fan running while I did it. I cleaned it with the hose while it was running. The fan kept going but today the reset was switched again and when I hit the button all I heard was a loud humming noise and no fan anymore.

After reading your website I see some areas where I have gone wrong but I'm wondering: is it the capacitor or the motor at this point?

The contacts are good and I know the compressor is kicking on because I can hear it. Another thing I noticed was how hot the unit seemed while I was waiting to see if the fan would turn on. What would be the most practical cause of my problem?

On 2011-08-11 by (mod) - Trane AC model XE 1000 capacitors

Michael often replacement capacitors are designed for more than one application. If your old, physically separate motor RUN capacitor had just two terminals they would be connected to a R (run) terminal and a (C) terminal on the motor. Tape off and don't use the third wire.

If the old capacitor was a Start/Run capacitor (incorporating those two different functions in one physical device) it would have had three wires, Start (wire to S terminal), Run (wire to R terminal) and Common (wire to common terminal).

On 2011-08-10 by Michael

I have a Trane AC model XE 1000. I am replacing the capacitors and the fan. I ordered and received a 370 volt oval run capacitor which looks just like the old one.

I also ordered and received a 440 Volt Round Dual Run Capacitor.

This one has three terminals on the top but the old one had two. I can see it is marked for "fan" "herm" which I know is for the compressor and "c" for common. My problem is I am only a lay person trying to install these parts and I am not sure of the correct placement for the wires on this 3 terminal capacitor.

Any help or suggestion would be appreciated. I have come this far and don't want to have the AC company come out now. Thanks.

On 2011-08-09 by (mod) -

Thanks for the nice note, Doug.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles.

Working together and exchanging information makes us better informed than any individual can be working alone.

On 2011-08-09 by doug ingram

this is awsome wish they had this when i started out in a/c

On 2011-08-09 by (mod) -

SR:
YOu need to identify the start (S), run (R), and common (C) terminals on the original equipment and connect those wires from your new capacitor to the same terminals. Unless the original capacitor is shorted, you can just leave it in place.

please review the article text above on this page and let me know what questions remain about the exact wiring connections for HVAC start/run capacitors.

On 2011-08-09 by (mod) -

QT, I have no doubt some techs know more than I about HVAC repair, but I'm a bit confused about why adding an extra condenser would make the compressor less hot.

The extra condenser may indeed make the outgoing liquid refrigerant (leaving the second condenser) cooler, and that would increase the efficiency of the refrigeration system. But all of that is on the output side of the compressor and past it's pumping cycle.

About replacing the start/run capacitor, it makes perfect sense to replace with same part numbers as the OEM equipment.

As the problem still exists I'd expect the tech to check the condition of the compressor itself - it may be drawing high amps and at/near end of life. Keep us posted - what you learn will help others too. Best. Daniel

On 2011-08-08 by SR

hi, I need to know the exact wires that I have to plug on the capacitors, because I am replacing the new capacitors, and I do not know What wires goes In what terminals of the capacitors, both in the fan unit as in the compressor unit, I would Kindly appreciate an answer, or if you have a diagram of the wires in the capacitors and fan and air conditioning unit, thank you. The unit is a Rheem.

On 2011-08-08 by QT

Thank you for your response,
The compressor from Copeland was installed 3 years ago. It worked fine though it was hot.

Recently an HVAC technician while fixing the defrost circuit of the freezer, he suggested to add the extra condenser into the current system. He explained that the extra condenser would make the hot gas cooler, then the compressor would be less hot.

After installing, the running compressor is still hot, but it becomes hard starting. The technician quits the job after replacing the relay and the cap (same part numbers), but the problem still exists. I am looking for the other technician to repair the problem now, but I really need the advices from the experienced person.

Thanks again DanJoeFriedman

On 2011-08-08 20:40:40.539086 by (mod) - freezer's compressor began hard starting after 35 minutes defrosting

QT I'm not sure I can adequately debut this by text Q&A, but provided you think that someone installed and wired the new start/run capacitor properly then a motor that is still having trouble starting would lead me to first::

- check that the new capacitor is good and also proper size
- that the new capacitor is wired correctly - both start and run wires

if those are OK the motor may have a bad start winding - a more detailed and sophisticated test of the motor might confirm that.

On 2011-08-08 by QT

My freezer's compressor began hard starting after 35 minutes defrosting (4 times to defrost a day). The motor starts but the potential relay continues to be on off for a while until the thermal protector shut down the power. The motor start and stop at least four times like that until it becomes running normally.

I changed the new start CAP and new potential relay, but the problem is still there.
I appreciate for your help to solve the problem.

On 2011-08-07 by Wayne Brass

Thanks for all your help.
Wayne

On 2011-08-06 by (mod) - Capacitor wiring instructions

Capacitor wiring instructions are on the package as well as in MOTOR CAPACITOR WIRING GUIDE

On 2011-08-06 by Wayne Brass

One more thing. If I do get the correct capacitor (40/440) with just 2 terminals. Will it matter which wire goes to which terminal as I don't think there marked?

On 2011-08-06 by (mod) -

Wayne a number of hard start or capacitor kits include wires that are not used in every installation - that's ok.

And as long as your motor is starting ok it should be fine. From what I've read among the EE experts and articles, a capacitor that is way too big could damage a system by not dropping out of the circuit after the motor starts - that's not your case.

On 2011-08-06 by Wayne Brass

Also this is a duel capacitor for COMP. & fan motor but it is only connected to compresser motor as the fan has its own capacitor.

It seems to be starting ok. But can this damage something in the long run ?

On 2011-08-06 by (mod) -

That's probably a somewhat weaker "get started" punch to the motor. Is it not starting your motor?

On 2011-08-06 by Wayne Brass

Is the 370 VAH instead of the 440VAC?

On 2011-08-06 by (mod) -

Wayne as long as the new capacitor is as close as yours is to the old one you are almost certainly OK - your old capacitor has the microfarad MFD or uF rating encoded in the data you provided as 40UF - that's 40 microfarads. Your new capacitor is rated at 45 MicroFarads - close enough.

On 2011-08-06 by Wayne Brass

My central AC capacitor was a Mallory C38Fb4440, 40UF 440VAC 60MZ proceted D. It was replaced yesterday with a 45+5 MFD 370VAH +05-05% 50/60 HZ. Is this acceptable?

On 2011-08-05 by (mod) -

Matching the start/run capacitor to the compressor or motor: Anon, quoting from our capacitor article above:

The particular starting capacitor to be purchased is matched to the horsepower range and voltage of the compressor or motor being repaired. Many motor starter capacitors to support a pretty wide range of motors. For example our sample capacitor was rated for use on 115V electric motors rated from 1/12 horsepower to 1/2 horsepower.

However, if you review our article above you'll see that we quote Supco in warning that a much-too-large capacitor could ultimately damage the electric motor by failing to remove itself from the circuit after the motor has started.

If you look at the typical start/run capacitor values in the AFCAP capacitor size table we've quoted above you'll see that start/run capacitors are typically described as having an individual operating range like 20/30 microfarads or 40/70 uf.

To me that means that if you replaced a 35 uf capacitor on an air conditioning compressor or fan motor with a 45 uf unit, it may well still fall within the original device operating range. But installing a much larger capacitor, such as a 108/150 uf device where a 35uf device was intended, would be a mistake and could damage the motor's start windings as we describe above.

On 2011-08-04 by Anonymous

Is it possible to install too large of a start/run capacitor and damage the compressor or fan motor? Say replacing a 35 micro-farad with a 45 micro-farad start/run capacitor?

On 2011-07-29 by Ed: Richmond VA at 107 F

Thank you for your great information, our 2 1/2 ton AC compressor failed to start! Turned out using the capacitor test process the duel starting cap was open circuit. For $27 at the local AC store and little wiring everything is up and running!
We are now cooling.

On 2011-07-25 by Mark

I've been in the hvac trade for 17 yrs, I know the cost of equipment isn't cheap, nor is the cost of refrigerant. The tools it takes to do these jobs. The many methods we have to go thru to make it comfortable. But I have also learned that in the end people don't care about superheat or subcooling or balancing out systems they just want it cool in the summer and warm in the winter!!!

On 2011-07-24 by (mod) -

Jerry it would be odd for an air conditioning blower unit fan to run backwards - unless it's miswired or suffered some strange electrical event that reversed the motor start direction. But combined with the motor not starting sometimes, it sounds as if you should try a hard-start capacitor kit before just replacing the motor.

On 2011-07-24 by jerry

why would the fan blow in different directions,,,,and sum time not start at all

On 2011-07-24 by (mod) -

Hey DIY Dan: we've posted more HVAC diagnostic procedures, equipment usage guides, and troubleshooting online than anyone else - so certainly we support informed homeowners and consumers, qualified DIY'ers, and also professionals in the field.

There are honest sharp workers and others who are more questionable in every field.

But with just a bit of training about HVAC servicing and repair, you'd become more aware of little mistakes that an amateur could make, simply by not knowing, that can lead to very costly damage to an HVAC system - like knot knowing how to purge lines on a test valve before it's connected.

That's why I recommend to serious DIY'ers on air conditioning or heat pump systems that they need to go to school on the topic.

On 2011-07-21 by DIY Dan

Have you ever worked on your own car? How about adding an outlet to your home?

But you're not an auto mechanic or licensed electrician!! Just holding a certification or license doesn't mean you know what you're doing, nor does the lack of such prove otherwise.

I thought car mechanics were crooks, hvac leaves them in the dust!!

On 2011-07-19 by (mod) -

It's not opposition to people learning to do competent, careful work themselves, but rather a reasonableness check that gives pause to a DIYers:

To properly diagnose a refrigerant leak and repair it, requires training in A/C theory, how equipment works, how to use test equipment, braze or silver solder repairs, evacuate, clean, and test a system for leaks, salvage and recycle the refrigerant, put a measured charge or proper refrigerant back into the system.

In addition to quite a bit of practical knowledge necessary, there is a considerable investment in equipment that includes

- halogen gas leak detection equipment

- soldering equipment

- HVAC vaccum pump

- gauge set

- containers of refrigerant gas

- containers and pump to remove gas from an existing system and place it in a recycling container

- refrigerant gas charge measuring equipment & heater to put in the proper refrigerant charge, per
and some other things I've forgotten in this off the cuff list.

All of that, if we put no cost on time to go to school, and no cost on the time to learn, test, and conduct the service job (which may be enjoyable to some, I agree), there is surely a thousand dollars or maybe three times that in equipment.

So for most homeowners it makes the most sense to hire a qualified HVAC tech to make the proper diagnosis and hopefully perform the proper and honest repair.

For an engineer or anyone else who wants to have the fun of diagnosing and servicing HVAC equipment, some jobs are much easier than others: diagnosing and replacing a bad relay, a start capacitor, or even a blower fan motor is far more manageable than the task I described above.

If you or any reader wants to prepare to tackle the broader range of refrigeration service needs on home or commercial equipment, by no means would I agree that it makes sense to just go buy some stuff and ask for a tip from a friendly HVAC supplier. Instead what makes sense is to take some classes in refrigeration servicing and repair

On 2011-07-18 by Concerned Engineer Paul

I have to say there is merit to what Joseph has mentioned and to Dan’s side as well.

As an engineer myself, it should be easier for the educated non licensed DIY guys to understand and buy components for HVAC.

Understanding the risks and rewards, no one should be shunned out of something they feel capable of saving money to do.

Let’s face it, we are not talking stocking parts at Home Depot or Lowes, rather allowing those individuals to seek and get council from their friendly HVAC distributor who can advise whether or not by meeting folks capable, to either support or discourage/recommend another way to repair.

The HVAC industry is like any other industry trying to protect its trade.

The amount of people willing to fix their own cars, perform major home improvements, plumbing, electrical work and even HVAC is very limited as the majority of folks just do not have an interest or skill set. The percentages are just not there to support protecting trades where 90% of the people just don’t care to DIY.

There are things that must be followed and understood to make sure your HVAC system works well, no argument here, but like Joseph says, the freedom to learn and make mistakes should be allowed for those willing to pay the price.

On 2011-07-10 by (mod) - agree with Joseph

I have to chime in on the side of the trained HVAC techs. Like many jobs, the less we know about what's needed the easier the job looks from the outside. Properly diagnosing and repairing HVAC equipment requires training, experience, special equipment to perform properly and safely.

That said, we outline at InspectAPedia lots of steps that a homeowner can do before calling a service tech to both save money and avoid wasting the tech's time: like seeing if the unit is turned on, that the thermostat is calling for cooling, and that the air filter is not clogged with crud.

On 2011-07-10 by Joseph--are you serious

Joseph, the reason the trade tries to keep the neighbor hood "Joe" from working on the units is for safety, t-stat-mercury filled swap to a new digital--where do properly dispose? Do you own a reclaim machine and tank? if not your dumping freon(probaly r22) do you own a vacuum pump and micron gauge?

then I bet your system if full of moisture and contaminets--probably R22 so it's alot more forgiving than r-410a,but I bet you already knew that. What did was your you tube method of charging? cold like a beer can? Listen Joseph I've been doing 15 years and run across guys like you all the time when I get stuck in a neighbor hood on a resi job, if it's so easy then why aren't you in the business making 90 a hour.

I know thats more than you make know, why not? We have insurances, overheads that you can't begin to comprehend. A good tech will charge the going rate and follow ALL the EPA giudelines, it's costs money to do our job. All the money is not pure 100% profit, how's continued training on real HVAC like chillers/ERU/ERV, geothermal etc...

resi work is the simplest form of hvac work, any moron can hook up a gauge and open a tank, but do you understand the principals behind what the refrigerant is doing? superheat/subcooling/ what are they? What do they mean? Once you've spent the time to master these things and realize that it's more than a 10 dollar part I can flip for 90, you'll understand why it cost so much

On 2011-07-09 by Joseph

Let me correct one thing. I did not replace the 3 ton A/C unit at the direction of an A/C tech. I was told by them that the cost to replace the unit would be $3500.00 I did the job for $500.00 and still working 5 years later (Used 3 ton a/c.)

On 2011-07-09 08:32:51.952063 by Joseph

The A/C trade is a scam. After I got taken for a ride many times and spent thousands of dollars by REAL A/C tech I decided to learn about this my self. I even replaced and entire 3 ton unit at the direction of a certified technician. Now I can use the Internet and youtube to get the most out of my A/C system. I installed my A/C system my self and it has worked great for almost 5 years now. Any tech that says that they would not buy from a supplier that sales to an unlicensed buyer is just a scammer.

He has no problem buying plumbing parts from Lowers or any and all electrical parts from a warehouse. The only trade that you are required to have a license is the A/C business and the reason is because the stuff is so simple that without banding together to keep parts out of the hands of the public there would be no way that they could charge $90.00 an hour.

Think about that for a moment. An A/C tech will try to tell you that A/C business is dangerous but so is installing a new breaker box and I can get one of those anywhere.

Is it the plumbing work that hey are concerned about? or perhaps the dreaded refrigerant? You can get refrigerant for your car at the auto parts store no problem. It's my home, It's my choice, It's my money and it's my risk. I now buy my parts on line and have saved my self thousands.

In the end I had to, as the end user, go back and learn to fix the screw ups that he so called tech made every time without exception.

On 2011-06-11 by Frank V Effenberger

There are two windings on the stator of a single phase induction motor. One is connected directly to the applied voltage while the other is connected to the applted voltage through the capacitor

. The capacitor shifts the phase of the alternating current through its winding relative to the other winding, thereby providing the torque needed to start and/or run the motor.

While the capacitor may accumulate charge, this is not its purpose. Poly phase induction motors need no capacitors, since the phases of the applied voltages are already shifted relative to each other.

On 2011-05-03 by (mod) - it is important to understand the use of capacitors in electrical equipment such as air conditioners.

We agree in part with Mr. Gardner that it is important to understand the use of capacitors in electrical equipment such as air conditioners. And when an air conditioner or heat pump motor won't "start" it can be difficult to determine (without proper expertise and equipment) whether the problem is with a starting capacitor or a run capacitor (if both are present).

Single capacitor electric motors are a lower-torque design and use a capacitor just to get the motor started. Some sources call this design a start-capacitor, induction-run motor.

Dual capacitor electric motors are a higher-torque design that use a higher-value capacitor to get the motor to start spinning, and a second lower-value capacitor to keep the motor spinning. In these motors a centrifugal switch switches from the higher to lower-value capacitor once the motor has started spinning.

The circuit diagram and installation/wiring instructions for a central air conditioner compressor unit will indicate the wiring and capacitor usage in the equipment.

Typically, if the compressor won't start or is hard-starting but the fan runs normally, the system might be repaired by installing a hard-starting kit (a start capacitor) or replacing a bad run capacitor (if one is used).

Some A/C and heat pump units use a combination capacitor that does both jobs that are accomplished by two individual (start + run) capacitors in other motor systems. If both the compressor motor and the fan motor refuse to start, it could be a bad run capacitor.

However a trivially simple electrical diagnosis and repair method is used by a great many service technicians. Opening the equipment covers the tech observes that a capacitor is bulged or damaged. S/he replaces that device with a new one of the same part number or rating.

A second trivial test used by some service technicians when a fan motor won't start is to use at tool to give the fan blades a spin (not your finger that can be cut off when the fan starts). If the fan motor starts and runs then we suspect a bad capacitor or a bad fan starter widing circuit.

A few readers asked about an A/C fan motor that keeps on running constantly even when the compressor has been shut off for a long time. An improperly grounded fan motor can cause this trouble.

Watch out: whenever an electrical component has failed it is important to understand whether the failure is endemic to the component itself, or whether the component failed because of a problem somewhere else.

Watch out: also for a failing compressor motor. An early symptom of a failing A/C or heat pump compressor is hard starting. Installing a capacitor may work, for a while. When the circuit breaker trips or fuse blows at compressor start-up, we suspect a bad compressor motor.

On 2011-05-03 by hhgardner@hotmail.com

Mr. Oiler reported that a start capacitor was bulging. It was most certainly a run capacitor.

Do not try to repair your own a/c unless you understand exactly how all components work. I, as a heating and air contractor, would never buy from a heating and air supply dealer that sold to unlicensed people.

...

Continue reading  at MOTOR CAPACITOR TYPES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see MOTOR CAPACITOR FAQs-3 - more recent Q&A about troubleshooting or replacing electric motor capacitors

Or see these

Recommended Articles

• BASIC ELECTRICAL TESTS for BURNED OUT COMPRESSOR MOTORS
• CAPACITOR TYPES, for MOTORS
  • CAPACITORS for HARD STARTING MOTORS
  • CAUSES of HARD STARTING ELECTRIC MOTORS
  • CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS
  • COPELAND ELECTRICAL HANDBOOK [PDF]
  • HARD STARTING COMPRESSOR MOTORS
  • HOW a STARTING CAPACITOR WORKS
  • HOW to TEST the MOTOR to ID TERMINALS
  • LOCATE the STARTING CAPACITOR
  • MOTOR CAPACITOR WIRING GUIDE
  • STARTING CAPACITOR SAFETY
  • TEST a MOTOR START or RUN CAPACITOR
• ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD
• ELECTRIC MOTOR DIAGNOSTIC GUIDE
• HARD STARTING ELECTRIC MOTOR CAUSES

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MOTOR CAPACITOR FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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