Q&A on hard-starting HVAC compressor motors:

These questions & answers about hard-starting air conditioner or heat pump compressor motors help diagnose why the motor may hesitage, be slow starting, or may continue to burn out the starting capacitor.

This air conditioning repair article series explains procedures for the diagnosis and repair of hard-starting air conditioning compressors.

FAQs on A/C Compressor Hard Start or Intermittent Run or Stutter

These questions and answers about HVAC compressor motors that have trouble starting were posted originally

at HARD STARTING COMPRESSOR MOTORS

Photo: a motor starting capacitor, a common repair effort for hard starting AC compressor motors. [Click to enlarge any image]

Question: condenser fan keeps running all the time

July 3, 2014) Boyd said:
my condenser fan runs all the time and i noticed it plows cool air, why would my unit not be warming up

Reply:

Boyd:

If you're looking for heat from a heat pump check that the thermostat has been set to heating mode.

If the condenser fan NEVER turns off then I suspect a relay or control board failure.

See

• FAN, COMPRESSOR / CONDENSER UNIT

Question: voltage problems with an LG 1.5 5 star AC

24 May 2015 Deepak Kumar said:
I am using LG 1.5 5 star AC from past 6 years recently we are facing some problem related to voltage. AC is working fine.

Whenever I switch on the ac in between 9pm to 11pm the voltage will fluctuate, after 11 pm it will work like charm. fluctuate means the outdoor unit will be running and their is no cool air is coming from ac. I need to restart the ac. Its been 3 months I am facing this issue. If I turn on the ac after 11 PM then their is no problem. Kindly suggest what I can do?

Thanks in advance.

Regards,
deepak

Reply:

Deepak

A problem with an electric motor (such as your AC compressor) might cause high current draw but I would not expect it to affect voltage.

Voltage is determined by your electrical supplier. I suggest starting by asking an electrician to check the incoming voltage at your electrical service, or perhaps to mount a monitoring device there.

Keep us informed and we'll take it from there.

Question: Haier 1.5 ton split ac after switching on it blows cool air for 10 minutes

26 May 2015 podeswar said:

i am having Haier 1.5 ton split ac after switching on it blows cool air for 10 minutes n then it blows hot air the complaint is not retifaing loaded gas changed coil changed condencer but the problem is not rectifaied the compressure is getting over heated

Reply:

Start by checking for cooling coil icing. See COOLING COIL ICING or LEAKS

On 2012-09-27 by Jesgrate

Rheem condensor only runs for 1/2-2 hours at a time and then quits. Have had a/c tech out several times.

Replaced breaker, changed wiring in thermostat, reconnected loose wire at furnace. Still not corrected. Could it be the thermostat? Unit is about 10 years old. Tech wants to come back and check 2400 ohms at furnace to same at condensor.

States if not same have to either replace wire in wall or I have a bad control board. Does this sound right?

On 2012-09-16 by (mod) -

Anonymous:

The refrigerant pressure behavior you describe sounds normal - normal pressures being developed when running and normal equalization when off.

I'm not sure the compressor is really OK - I'd suspect a control board except you report that the compressor motor gets abnormally hot. See ELECTRIC MOTOR DIAGNOSIS tests for details that explain that testing an electric motor (like a compressor) when it is not running are helpful but incomplete.

Or perhaps check the maunfacturer's specs on operating temperatures for the compressor and compare those to what you are actually seeing. Keep us posted - what you find may permit more comment and will also help others.

On 2012-09-15 by Anonymous

Problem: AC compressor starts and runs for 30 to 45 seconds then shuts off. Compressor 220v /1 phase 2.5 ton scroll. During this time it gets very hot..then cools off and would restart again to run for only 30 or so seconds. Fairly new compressor less than a year old.

Checks already done: All start and run capacitors checked and are good./

Compressor windings checked across all three terminals and ohm out good./ Potential relay is checked and cuts it out of circuit as designed with amp meter./ Voltage is good. / When guages are attached to high and low side and the compressor starts the pressures move as designed both high and low.

When it shuts off they equalize. In other words no high head pessure etc.
Question: Could the internal heat overload protection be faulty...i have rarely seen this.

On 2012-09-09 by jayvan

b4 u mention about ur aircon problem u should diagnose carefully check all electrical coponent b4 u give the cause of the problem sometimes the problem coming from the tech w/wrong diagnose of the units make it sure that u should check it all one by one thanks

On 2012-09-06 by (mod) -

Jack, often a humming and delayed start means that there is a bad start/run capacitor or a bad motor. I'm not certaint that your capacitor test was complete (though it was a good idea) - for example if a motor is hard starting and a cap defective, it may seem fine when mounted at another motor that is not hard starting.

There are some compressor measurements & tests that look for an open winding or a dead short as well as for high amps current draw during startup - I'd check those. WATCH OUT for electrocution hazards - if you're not trained and equipped be sure to ask for expert help.

On 2012-09-05 by Jack

P.S.
Also checked breaker and relay, they are also good.

On 2012-09-05 by Jack

My compressor fan works fine but when the unit is switched on the compressor makes a loud hum for about 2 seconds without starting and conitnues to repeat the hum about every 7 seconds.

I think the compressor is locked up but not sure. The capacitor is good (tried it on another unit). Also did ohm test and it checked out fine. What else can I do to trouble shoot it before I replace it?

On 2012-09-02 by Anonymous

After my central air conditioner works a long time to get to the set temperature, when it shits off and then restarts when temperature rises the circuit breaker pops

I had a booster installed but did not help. So this week I installed a super booster but it started the fan but not the compressor. So I shut off the system for two hours and the compressor worked fine. Now over the weekend I kept the thermostat on 74 so it did not have to work too long at a time and it worked fine.

My question is what could be the problem and how can I repair it?

On 2012-09-02 by Paul P

When the A/C unit attempts to start, the blower fan on the Compressor Unit starts but you can hear a Surge of Power that dims the lights and you can hear at the surge at the power panel but the compressor hasn't started. There may be as many as 5 or 6 surges with 10-15 second pauses between them and then the compressor kicks in.

Our A/C Tech checked the system and said it's numbers are all with in the limits of normal operation .
The Surge Of Power trying to start the compressor can't be normal. Not only am I concerned with the A/C Compressor damage but my power bill with all the surges.
Any suggestions welcome..

On 2012-08-26 by jose

What amp breaker do you use for à 4 ton ac unit?

On 2012-08-11 by Chuck

Thanks!

On 2012-08-11 by (mod) -

You could be seeing a voltage drop across the wire - usually the electrician looks at the anticipated current draw or circuit amapacity requirement and the length of wire run and finds the NEC table that suggests at what length to go to a larger wire size. I'd also suggest a very careful check of the connections themselves. For example a corroded aluminum wire connection could be trouble.

On 2012-08-10 by Chuck

Question about a long run. We have a 5 ton unit (8 years old). Bought the house from the builder. Unit is regularly serviced, but it has always had starting pull that you can "feel" in the house. The unit has a hard start capacitor, which appears to be working.

The electrical run to the unit is long, however. It's about 80' from the breaker to the unit. I'm wondering if a larger wire may help the start? Curious about my options! The "buzz" and dim lights when the unit starts (again, did this from day 1) would be nice to solve! Appreciate the time you all take to answer questions like this.

On 2012-07-27 by (mod) - "how long can the unit stay on trying to reach set temp

Cristie

Regarding "how long can the unit stay on trying to reach set temp" the answer is ... it depends. It depends on quite a few variables such as

- the outside temperature

- the inside temperature

- the rate of heat gain of the building, sun exposure, weather, direction orientation of walls

- the SET temperature of the thermostat

- the capacity, design, of the cooling system

- the cleanliness of the air filter

- the presence or absence of duct defects such as crimps, or crushed ductwork or air leak

Since some of these variables are different from hour to hour and day to day - weather - and others vary by human action - thermostat settings - we can't expect there to be a standard number of minutes or hours that a cooling system will stay "on" trying to reach the set temperature. In fact if we make the set temperature low enough the cooling system will run forever without reaching it.

A more helpful question to ask is: does your system seem to be working differently than it used to - taking weather changes into consideration? and is there good air flow at supply registers and is that air cool?

On 2012-07-26 by Cristie

I did slightly bend a few cooling fins but I fixed them back to normal but what else I need to know is b4 I cleaned dust off the evp , could dust have gotten sucked through cooling fins and clogged something? I know the outside drain hole isn't plugged up so maybe some other area?

I know it ran great a yr ago new with 95+ degrees outside & now it doesn't get as cool as it should and my MAIN question was/is how long can the unit stay on trying to reach set temp I remember it cycled more frequent than before I cleaned evp... I don't want to blow my window unit ..any help, PLEASE

On 2012-07-25 by Anonymous

Christie the equipment should be able to run as you describe.

And while there may be more to your question than was evident, if dust was removed from the evaporator coil that's good, helpful, and not harmful - let's hope no one bent or crushed the cooling fins.

On 2012-07-25 by Cristie

Will dust covering the evp coils but then sucked out cause a problem fo the window unit?

Is it ok for my window unit to run with cold air without taking a break even though the desired temp isn't reached.

When I first bought unit it seemed to cycle off & on and now when on coldest setting it isn't cutting off is this going to break the unit does it have to cut off (the compressor) I guess or is it ok to keep running hours or until desired temp is achieved please tell me

On 2012-07-14 by Roland

Thank you!!!! You saved me a lot of trouble and expense with your article on the capacitors and all the other excellent information

Thanks again

On 2012-07-08 by Charles

Outdoor A/C unit. Temps in the high 90's. Found compressor running, but fan stopped.

Found badly corroded connection between condenser fan and capacitor. Female connector was burned and barely in contact. Wire charred for about 1/2" at connector. Removed burned end of wire, scraped the copper, replaced connector. Unit ran normally until the next day.

Now starts normally, but 20 to 30 minutes later,the condenser fan shuts off. Feels hot from mounting point. Compressor still running. Shut system off for 30 minutes. Repeat, unit starts normally etc. When running, the inlet line is cold and dews normally.

Cleaned all contacts on capacitor. No change. Fan runs until the case temperature is around 130 degrees, then shuts down. Fan case temperature then climbs to 146 degrees before beginning to cool.

Tried to check capacitor. In checking resistance, got no reading. Then put voltmeter across terminals and registered a declining voltage. Capacitor MAY be okay.

Checked voltage. Ran 240V from T1 to T2, 108 to 112V from capacitor to T2.

Still not sure what the problem is, but starting to suspect the fan a bit more.

On 2012-07-01 by Anonymous

if compressor and the fan motor do not come on what can be the problem

On 2012-06-30 by (mod) - system runs for 10 minutes and stops

ColdShot,

If the system runs for 10 minutes and stops, it could be overheating - maybe a failing motor; it's common to try swapping in a start/run cap first though.

On 2012-06-30 by xXxColdShotxXx

I have been having problems with my outdoor A/C unit. It will start, but after 5 to 10 minutes the motor just stops turning and it just hums and it starts blowing warm air through the ducts. What do you think may be wrong with it, is it a bad capacitor or relay or what? Thanks for any help.

On 2012-06-21 by John

Thanks very much for the advise!

On 2012-06-21 by (mod) - I have to bang the side of my York compressor to get it started

John,

Sometimes when mechanically disturbing an appliance gets it running we trace the problem to a bad start relay or contactor, or to a loose electrical connection. I'd as the service tech to check the system's operation for those or some other difficulty.

On 2012-06-21 by (mod) -

Amanda, you need to as your HVAC service company to send out an experienced service tech. The problem may be a hard starting motor - or something else, we can't tell from your email.

On 2012-06-21 by John

Hello, Appreciate any help; At the beginning of each summer I have to bang the side of my York compressor to get it started.

The fan blades start spinning and the compressor kicks in immediately after I bang it with my hand. I’m banging the area where the capacitor and wires (switch?) reside. The unit is nine years old. Any idea what part(s) may be bad?
Thanks very much!!

On 2012-06-20 by amanda

any help will be really appriciated.. ive been having many issues with my air this yr which is aggravating since the unit is only 3yrs old..

first i had a issue with it not cooling and i had a tech out he said my coils needed clean so i had that done and it worked good for 2 weeks now it struggles to keep up it never gets as cool as what the thermostat is set to if i have it set on 72 it will get to 74 but not any lower, now in the late afternoon or early evening the outside unit turns off (furnace still running)

i check the breaker and its never tripped but the only way i can get it to come back on is if i turn the breaker off for a minute and turn it back on. the first time i did that it came right back on but the second and third time i had to do it a few times before it would come on.. the pressures have been checked and they seem to be what they are suppose to be.

i have a child with medical problems and she cant be in the heat, and im lost on what to do my grandfather was a repair man yrs ago but with things being more "updated"

and hes not familar with a/c with heat pumps now he doesnt know where or what to do and with my finances being tight he doesnt wanna cost me money i dont have replacing things that dont need replaced..thanks for any advice

On 2012-06-19 by (mod) -

NB

Except when the service tech is diagnosing and fixing a problem, there is just a little simple annual service/inspection that is needed for the outside compressor/condenser unit. Inspect the unit for physical damage such as smashed cooling fins, debris blocking the cooling fins on the condensing coil, obstructions sticking into the unit, trash and debris or shrubs around or close to the unit that might obstruct air flow or interfere with fan operation.

A more subtle inspection point involves noticing oil deposits on the refrigerant line service ports - indicating a refrigerant leak.

Other defects such as loose components show up as sounds or noises.

Still other defects that need repair include signs of loose or burned wires, lost refrigerant piping insulation, unit out of level.

On 2012-06-18 by N BALASUBRAMANIAN

HOW OFTEN IS THE OUT-DOOR COMPRESSOR-CONDENSER UNIT IS TO BE SERVICED

On 2012-06-18 by (mod) -

Tim, you have already done the hard part of this diagnosis.

Dimming lights can indicate that an electric device is drawing high current - which in the case you describe may be the compressor motor trying to start. The cycling is because it tries, overheats, stops on thermal reset, cools off and tries again;

The burned wire you found at the capacitor may mean that (if you are lucky) just the capacitor has failed - replacing it may get that motor running again. But if the compressor motor itself has seized, replacing the capacitor will show that the motor still can't start.

"BURNED-OUT COMPRESSOR" discusses how we diagnose a burned out compressor.

(Found in INDEX to RELATED ARTICLES at our Continue reading suggestions at the end of this article)

and at "CAPACITORS for HARD STARTING MOTORS" we discuss troubleshooting the start/run capacitor.

WATCH OUT: if you are not trained and lack expertise, you can be shocked or killed (or start a fire) working on electrical equipment.

On 2012-06-16 by Tim

After I noticed my central air wasn't cooling I turned it off for awhile and tried to re-start, I noticed that every 20- 30 seconds my lights would dim a little as if a large electrical draw then release. I turned the system off and began researching this site ( an excellent service I might add).

I took the cover off the unit out side and immediately noticed the red wire connected to my capacitor was just resting on the terminal as it was completely burned and charred. Did I get lucky and find the problem or do you think this is a symptom of a different issue.

On 2012-05-30 by (mod) -

Thanks Ronald for the very nice comments. We work hard to make our information useful, accurate, unbiased. So reader feedback, including questions, comments, and polite debate, are very helpful.

On 2012-05-30 by (mod) -

Thanks Anthony, your views are helpful, though I'm not sure we agree; a burnt up wire could be caused by a variety of problems, even a nick and short circuit, but more likely by overheating due to overcurrent due to a problem in a relay or in the compressor motor itself. A burning up wire to a compressor is less likely to damage the compressor than vice versa.

On 2012-05-29 by Ronald

I want to Thank You for posting this wonderful info....I was able to follow your instructions and get my AC up and running..!!!

To those who are attempting to D.Y.I...make sure your circuits are off ..!! I am a Residential Remodeler by trade and am well versed in working with electrical and I still checked and double checked that everything was off before working...Good Luck..!!!

On 2012-03-26 by Anthony

I am an E.E. The comments above regarding the "Could be" is correct, in fact I would say it's likely a burnt wire caused the comp to fail. Greater than 90% probablilty based on the outline of events. However, a lot of what was described above regarding motor start up in the reply is misleading, and somewhat incorrect.

On 2012-03-17 5 by I am having central air conditio

My central air conditioning unit has been giving me trouble for a few years now.

Sometimes, when you turn it on at the thermostat it works, and sometimes it doesn't. If it does work, it usually quits before it should. A fan or something is still going, but the cooling part that makes the louder noise outside quits running. Sometimes, you can manipulate the spring thing at the thermostat by pulling it back and letting it go and it will start. Do you know what the problem could be? Thanks.

On 2012-01-09 by (mod) -

Samy,

I'm afraid the answer is a definite ... maybe. For example if the compressor was slugged with excess liquid refrigerant it could have been internally damaged.

Also, and this is not quite an "excess" of refrigerant gas, on some, at least older refrigeration systems, if someone switched the elecrical power on and off too rapidly or too frequently, the compressor could find itself trying to re-start against a high head pressure - with difficuly.

Whereas normal on-off (less frequent) cycling on and off of the compressor gave the gas pressure time to equalize between the high and low sides of the system, reducing head pressure and giving the compressor an easier re-start.

Finally, a clog or blocked refrigerant line that slows or does not let the high pressure side bleed down and equalize when the compressor is off will also make the compressor hard-starting.

On 2012-01-09 0 by samy salman

could an excess of the coolant gas cause hard start up problem ?

On 2011-12-24 by (mod) -

Mel I think there is no need nor reason to install an extra start capacitor when the present one is working adequately.

The addition of a hard start capacitor kit makes sense if your existing capacitor has failed, OR if you are trying to squeeze a bit more use out of a failing hard-starting compressor motor.

My reasoning is that if we exclude a motor that is hard starting because the capacitor is bad (just replace the capacitor) then other reasons for hard starting motors are not innate to the capacitor but to other causes that won't be avoided by the capacitor.

Comments welcome.

On 2011-12-23 by Mel

Should a "Hard-Start Kit" be installed on an air conditioner when no problems arise? Will installing one prevent problems and will the a/c unit last longer if installed?

On 2011-12-06 by LEONCIOMADRONERO

HOW MANY YEARS THE LIFE SPAN OF A CAPACITOR OR WHAT IS CAUSE THE CAPACITOR WILL BUSTED

On 2011-10-09 by Peter

DanJoeFriedman, thanks for your advice...I requested a more experience tech, who was able to locate some lose wiring that has seemed to fix the problem...All best, Peter

On 2011-10-03 by (mod) -

TX Red: slow pressure equalization when the compressor is OFF indeed suggests a blockage that needs to be found and fixed; perhaps at a drier/filter or at a thermostatic expansion valve or cap tube.

Dan F: it sounds as if your compressor is not starting. You need a service call. Possibly a hard start capacitor kit will help but I'd like to see some diagnosis first.

Chandra: back in Sept you described what sounds to me like an overcurrent due to a seized motor. What did your service tech find and do?

On 2011-09-19 by Waqar Zaidi

Hi DanJoeFriedman, my 4 months old AC is having starting problem as i told you previously, i observed that when the compressor starts for the first time its take 2 to 3 tries to get start then works fine even after its thermostat gets satisfy it starts again fine. what could be the reason of 2 to 3 tries to get start 1st time?

my breaker never triped and its compressor never stop working while running it stops only when i stop it or its desired temperature reached. cooling is also fine no icing etc. i am concerned about its compressor only is it fine coz its new and in warranty.

On 2011-09-14 by dan f

When set to cool, my a/c makes a humming noise for about 30 seconds before quitting and not blowing anything. What can I do?

On 2011-09-09 by Texas Red

...not exactly sure what a compressor start relay is. Is it wired into the compressor itself, or is it located in the control box among capacitors, terminals, etc?

If its contacts were burned or otherwise damaged, wouldn't the solution be to replace the relay rather than install a hard start kit? I watched the intallation of the hard start kit and am pretty sure he just confirmed that the compressor was drawing too much amperage at start up and therefore required the kit.

He attributed the high start up draw to slow pressure equalization somewhere between evaporator, condensor, compressor(??) Not sure specifically where or how the uneven pressure was creating a problem.

On 2011-09-09 by chandra

Please also provide cost if there is any problem or repair requires, thanks again!

On 2011-09-09 by chandra

My attic fan or blower makes huge sound and circuit breaker trips off when I start my AC. I bought the new home 3 years back and we use AC very less as we prefer outside air. Please share your experiences or let me know if you know the problem or resolved the similar problem. Thank you!

On 2011-09-08 by (mod) -

Your thesis is reasonable but not, IMHO, absolutely proven by events.

A compressor start relay (or most other switches) that are loosely wired will typically experience arcing at the loose connection (an event that can, by the way, when the circuit is active or the switch closed, draw higher amps than normal due to the resistance at the point of arcing and corrosion.)

I've posted our conversation in this article in the Q&A just above the Comments Box section.

On 2011-09-08 by Texas Red

Thanks, Dan. I didn't communicate the timeline very well in my original post.

In 2009 tech # one had come to respond to my problem of a 4-year-old compressor kicking the circuit breaker. Without even looking at the connections in the shut-off box adjacent to the unit, he went straight into control panel, checked compressor current draw at start-up and installed a hard-start kit. I thought it odd that a compressor less than five years old would be drawing too much current.

Had no problems in 2010 but last month the circuit breaker started kicking off again late in the day. Tech #one returned, checked coolant pressures and return temp, added some freon and started to pack up.

I asked if he wasn't going to check the current draws. He reluctantly removed the control cover, checked draw and voltages and pronounced the unit was running perfectly before leaving with my $168 check. When the circuit breaker kicked off again the next day, I started to suspect the breaker might be worn out.

Called an electrician a few days later. He replaced the breaker switch, again without checking the connections at the shut-off box, and within eight hours my compressor had died - coils shorted to ground - confirmed by tech # one who quoted me a price to replace the unit.

Now I called a contractor I knew asking if he knew any good AC techs. He referred me to tech # 2 who, in my first call, was immediately suspicious that my original problem may have been in the wiring, not the unit. His reasoning was that a compressor less than 5 years old shouldn't have been giving me problems to begin with.

He came over to confimr my compressor was shorted out.

He then did what no other tech had done since I owned the house - popped the cover off the shut-off box and tightened the leads at the terminals - black wire loose, white wire "very loose." My question is whether that may have been my problem all along and would a hard-start kit have temporarily releved the symptom -tripped circuit breaker- without curing the problem.

On 2011-09-05 by (mod) -

Josh a bad capacitor can cause revresopreation, Ty replacing the start-run cap

On 2011-09-05 by Josh

My (indoor) fan motor studders and goes back and forth in forward and reverse. It finally starts turning in the right direction but it doesent have full power, and then it eventually dies down to a slow creep and begins to make a light humming noise..

I think it may be the Dual Capacitor... Could anyone help me with this problem, any advice will be greatly appreciated...

On 2011-09-01 by (mod) -

Julius:
An HVAC compressor that does not produce any pressure sounds as if it's broken internally. I'd ask for a check by an HVACR technician

Byran: it sounds as if you have a hard-starting compressor - it may be at end of life but often it's worth asking an HVAC tech to try an hard-start capacitor kit.

On 2011-08-28 by Julius

My compressor runs but does not pump ( pressures remain equalized) it eventually shuts off and then runs again but with the same results. Doe you know what is causing this?

On 2011-08-27 by Bryan

Compressor will not start. Fan runs, air handler fine. When I pulled the outside (fuse? the electrical plug on outside wall that disconnects the electrical input) and then push it back it, the compressor begins to start, for a second, then stops. The top of the compressor/condenser unit stays warm, steam comes off of it when water squirted on it.

On 2011-08-26 by (mod) -

Scott, did you look at the HVAC noise diagnostics beginning at NOISY AIR CONDITIONER / HEAT PUMP (Found in INDEX to RELATED ARTICLES at our Continue reading suggestions at the end of this article)
There we discuss humming and buzzing noises and possible sources. You need to start by being sure you have traced the sound to a specific piece of equipment; then look at motors, capacitors, relays as we describe in the article.

On 2011-08-26 by Scott

2nd Request...My Central Air unit (Carrier) makes a buzzing/humming noise briefly when it starts. Kind of like a transformer winding noise. It is not heard at the compressor unit. The fan circuit has also been ruled out by disconnecting the compressor circuit and starting the furnace fan, etc. Any suggestions??

On 2011-08-26 by (mod) -

Clare I doubt anyone can even guess at a diagnosis of what's wrong with your system with so little information, but it's reasonable to ask the service company to return and figure out what happened. Let us know what you're told.

On 2011-08-26 by (mod) -

Peter, talk with the HVACR service manager before having anyone sent out again. Politely ask him to send someone with much experience and training so that you don't keep repeating service calls. It may seem profitable to the service company to keep returning, but I doubt they want a bad reputation.

On 2011-08-25 by Clare

Would anyone know what these guys could have done to my unit. Have never had problems just had it serviced once a year.

I had our air units serviced yesterday and now one unit's fan will not run ?

On 2011-08-20 by Peter

a few months ago my condenser began shutting down before it would reach its set temperature... had service in who replaced a circuit board after much deliberating and I think a capacitor...It worked perfectly for a few day through a stretch of 100+ days...then it returned to its previous behavior..

.I didn't use the system and checked for a once or twice a week to see if the rest had done some good...

About 4 weeks from the last time it worked properly, I tried it again during another 100+ degrees spell and it worked like a champ again...consistently lowering the internal temperature nearly 30 degrees from the outside..

.This lasted for about 4-5 weeks and three days ago returned again to it previous bad performance..

.I have had service twice and am gettng ready to make another call...

Any thoughts? Many thanks, Peter

On 2011-08-16 by tammy

fabulous info. thanks

On 2011-08-15 by (mod) -

Stanley typically when the compressor/condenser shuts off and won't operate for several hours it's a sign that a motor is overheating and being turned off by a safety switch. Often thermal overload switches on electrical equipment will automagically reset themselves once the equipment has cooled down.

If it's your outside compressor/condenser unit that's switching off you can confirm that it's overheating by gently cooling the system down with a garden hose (it is designed to tolerate rainfall, for example).

If your unit has blocked airflow due to shrubs or something else or if its condensing coil or fan are blocked by debris (like grass clippings) it may be possible for a homeowner to fix that condition by cleaning or hosing off the equipment or cutting back shrubs too close to the unit.

In any other case you need an HVAC tech to diagnose and fix the cause of overheating.

On 2011-08-15 by Stanley Franklin

Air conditioner starts however after about 5 hours the outside unit shuts off and then won't come back on for several hours.

On 2011-08-08 by (mod) -

Sam provided the new capacitor is properly selected and wired up, it's time to have some tests of the motor itself, its start and run windings, to see if it's usable.

Other diagnostics can rule out a problem, for example with the thermostatic expansion valve or a refrigerant system clog that was causing overpressure and the motor to go off on reset.

On 2011-08-08 by Sam

On 8-6-11 a a/c repairman put a hard start kit on my unit, later the unit stop cooling. He
came back and restarted the compresser, again a few hours later it stop cooling. What to do at this point, please advise me.

On 2011-08-07 by tungnguyen

how much for replacement the motor of air conditioner ,

On 2011-08-06 by (mod) -

tripping circuit breaker means overcurrent means a motor that either cannot start or is seized.

On 2011-08-06 by Mark

My condensor trips my circuit breaker, the compressor fans starts but not the compressor(Nor does it hum). When I try to short the capicitor there is no spark. Is it possible that the capacitor is to blame or more unfortunate, the compressor?

On 2011-08-05 by (mod) -

I think the thing to do is take out the motor and test it stand-alone.
I'd think your tech would also check

- proper wiring connections

- proper voltage (not low voltage)

- that the motor ratings and wiring connections match the actual voltage (some motors can be wired for 120 V OR 240V)

- that there is no binding in motor mount or drive - if the motor were not properly mounted, or if the fan it's trying to spin has seized bearings or a crooked, bent shaft, the motor may be unable to turn the blower shaft - that's a reason for testing the motor out of the unit.

If all of those look good it must be a local wiring or control board problem. But the humming sure sounds like a bad motor, capacitor, or low voltage.

On 2011-08-05 2 by Amy Sparks

even if we just put a brand new motor and capacitor in it? could it be anything else?

On 2011-08-05 by (mod) -

Amy you may have a bad fan motor, bad start relay, or control board.

On 2011-08-05 by Amy Sparks

the unit comes on hummms light air flow...fan not turning. replaced fan motor and capacitor. does the exact same thing! light air flow hummm but fan not turning! help!

On 2011-07-29 by (mod) - thanks for the Kudos to InspectApedia - we take care to remain independent & unbiased

Thanks for the nice note Ms. Ruiz. We publish information in some depth on most building topics. Among problem diagnosis and repair steps, there are many that are well within the scope of most homeowners or occupants, but of course other steps require expertise and special equipment.

Even in the latter case the more you know about the general approach to solving or preventing building troubles the better you can understand what's being proposed or done by your contractor.
InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

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 2011-07-29 by Bertha V Ruiz (female)

Thank you so much for this info. I am trying to familiarize myself in how hvac works. It hcosts so much for any service call. Not to mention the labor and parts. I am glad that this info. is free for one to just read and take notes. to know-how and what to look for.

On 2011-07-28 by (mod) -

Chris short cycling A/C compressors combined with that loud startup noise sounds like the system is shutting off on thermal reset. I can't say if it's a bad relay, control, or motor, but you need a service call.

On 2011-07-27 by Chris

My A/C unit just started turning on and off very frequently.

The unit starts, making a loud noise at first, runs for about 20 seconds or so, then shuts down. This is a continuous cycle. The system is about 10 years old, and I have not been running it very hard, with the temp set at 85 degrees. Any clues as to what the problem is?

On 2011-07-24 by (mod) -

Anna what's recommended - a hard start kit - for your compressor motor - sounds like a reasonable thing to try in that it's much less costly than replacing the A/C system. If your mobile home park has inadequate power service to the whole community you might see that as low voltage (that can be measured or even monitored) or perhaps dimming lights.

On 2011-07-22 by Anna

Sometimes my ac will come on and sometimes, it will not. I was told the problem is because I live in a older mobile home park that can not handle the amount of power needed for the 105 residences to run ac units on a hot day. I was told I should have a hard start installed on my ac. It is a Rheem 2.5 that is approx. 10 yrs old. Does this seem logical?

On 2011-07-19 by (mod) -

Christopher:

To get a functional transfer of heat from the condensing coil to outside air we need at least 15 degf. temperature difference.

When the weather is extremely hot outside it might be that for some systems the ambient air temperature is getting close enough to the temperature of the high pressure high temperature gas exiting the compressor (and entering the condenser coil) that the system has diminished cooling capacity. Temporarily cooling down the whole outside system increases the system efficiency but only briefly.

Make sure your compressor has good air flow, not blocked by a building, plants, etc; some folks try adding shade over the unit; If it continues to overheat I'd ask for an opinion from an experienced local service tech.

On 2011-07-19 by (mod) -

Bob: the way most capacitor kits work they are intended to be added on to the existing wiring in parallel. A second capacitor wouldn't damage the compressor so much as keep a failing compressor limping along a bit longer before it seized up for good.

On 2011-07-18 by Christopher

My air conditioner compressor runs fine till it gets really hot outside, about 3:30 I have to get out the hose and spray off the lines and then it will start and run all night. Any Ideas what is wrong the unit is only 6 years old and has always done this.

On 2011-07-18 by Bob:

there are two hard start kits on my air conditioner. I know that there should only be one but some tech installed a second one a few years back and didnt remove the first one. My question is would having two hard start kits cause a compressor to go bad.

On 2011-07-06 by (mod) -

Brent: RE: One of the connections on my compressor has literally burned up. I replaced the cable/connection and cleaned the lead on the compressor but the compressor still doesnt come on"

a burned up electrical wire connection at an air conditioning compressor can happen for several reasons but one of them is that the motor is frozen and can't start; when the stuck motor tries to start it draws high amps and can over time burn the electrical connection before the breaker trips. Sounds like you need a service call from a trained tech.

On 2011-07-06 by (mod) -

Andre: re: "my compressor won't turn on" - if you hear the motor trying to start but it's not starting you might be able to get the compressor going by having a hard starting capacitor kit installed.

In the article series

COMPRESSOR & CONDENSING COIL, A/C

see the article titled CAPACITORS for HARD STARTING MOTORS

(Found in INDEX to RELATED ARTICLES at our Continue reading suggestions at the end of this article)

On 2011-07-06 by (mod) -

Eric: re: "100 degree days have my compressor shutting down during the hottest part of the day" - your compressor may indeed be at end of its life, but there are some things to check: can you make sure it's got good air flow through the unit, that the compressor is not too close to the building, blocked by shrubs or trash?

You could also try temporarily shading the unit with a beach umbrella to see if that makes a difference and extends its life.

On 2011-07-06 by Eric Y

I live in Texas and lately the endless 100 degree days have my compressor shutting down during the hottest part of the day. If I spray cold water it comes back on and runs the rest of the day. The AC Tech says I need a whole new unit. What's your take on this.

On 2011-06-23 by andre

my fan run but my compressor won't turn on ....i hear it tryin to jump on but it wont..what do i do for this problem

On 2011-06-19 by Brent

One of the connections on my compressor has literally burned up. I replaced the cable/connection and cleaned the lead on the compressor but the compressor still doesnt come on. Any ideas?

On 2011-06-16 by (mod) -

Brenda: re: "i have changed the breaker the capacitor switch and it sparks when i turned the breaker on "

This sounds DANGEROUS - leave the equipment off until it's checked by a trained HVAC tech or a licensed electrician. I can't say if the failure is in the equipment, wiring, or breaker/panel but it sure sounds like a short circuit that could start a fire.

On 2011-06-16 by (mod) -

Craig:
Yep, it could be a bad start / run capacitor - and that's less costly than replacing a bad fan motor so I'd try that. Can you spin the fan blades easily (with power off) ? If so the motor is not seized up fully (yet)

On 2011-06-09 by Craig Barnes

I have a blower fan that will not continue to run...It will start to rev up than it's like the voltage drops and it slows that stops ?... can this be a start Capacitor problem?

On 2011-06-09 by brenda

i have changed the breaker the capacitor switch and it sparks when i turned the breaker on

On 2011-06-02 by (mod) -

Grant: that question is beyond my expertise - I'll do some research on starting capacitor options and will report back here.

On 2011-06-02 by (mod) -

Lonny, did you check the circuit breaker at the main panel?

Provided that you are trained and know how to safely make basic electrical checks, if you have power at the main panel, then shut off power there (on the circuit to your compressor unit) and check the continuity of the wiring and wiring connections.

Watch out for fatal electrocution hazards!!

On 2011-06-02 by lonny

Had a compressor not getting power,change the circuit breaker still not getting power to the unit

On 2011-06-01 by grant

i have been asvised that on a hvac run capacitor, 370volt can be replaced with a 440 volt(45+5 uf) and that compressor will only draw power that is needed and extra available voltage wont cause a malfunction..is this correct?

On 2011-05-21 by (mod) -

Yes, a starter capacitor can fail without bulging. If in doubt it's often an inexpensive diagnostic test to simply swap in a new one.

On 2011-05-20 by Frank

If a start capacitor goes bad, can it just get weak or will it most likely bulge out?

...

Continue reading at HARD STARTING COMPRESSOR MOTORS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HARD STARTING COMPRESSOR MOTOR FAQs-2 - more-recent questions & answers about HVAC or heat pump compressor motor starting trouble

Or see these

Recommended Articles

• COMPRESSOR / CONDENSER REPAIR - home
  • BURNED-OUT COMPRESSOR
  • CAPACITORS for HARD STARTING MOTORS
  • COMPRESSOR / CONDENSER DIAGNOSTICS
  • COMPRESSOR / CONDENSER INSPECTION CHECKLIST
  • COMPRESSOR MOTOR INSULATION
  • COMPRESSOR MOTOR REPLACEMENT
  • CONTACTOR RELAY DIAGNOSIS & REPAIR
  • CONTROL CIRCUIT BOARD, A/C
  • CRANKCASE HEATERS
  • FAN, COMPRESSOR / CONDENSER UNIT
  • HARD STARTING COMPRESSOR MOTORS
  • MOTOR OVERLOAD RESET SWITCH
  • NOISES, HVAC SYSTEM DIAGNOSIS - home
  • REFRIGERANT FLOODBACK, LIQUID SLUGGING
  • TIGHT or SEIZED AC COMPRESSORS
• ELECTRIC MOTOR DIAGNOSTIC GUIDE tests to diagnose electric motors

Suggested citation for this web page

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

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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