Q&A on what to dow when your air conditioner or heat pump won't start: FAQS about what to check if your air conditioner or heat pump just won't start at all.

This page is part of our series on how to diagnose an air conditioner or heat pump that is not cooling: this article explains how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity, reduced or no cool air flow, reduced or no actual lowering of the air temperature, or an air conditioner that won't start.

Q&A: What to Check First if the Air Conditioner or Heat Pump Won't Start

These questions and answers about diagnosing and fixing an A/C or heat pump unit that won't run or won't start were posted originally

at AIR CONDITIONER WON'T START - home; be sure to review that article.

AC fan motor slows, hums, won't run

Ac fan wouldn’t start could manually press contractors an it takes off a few hrs later can motor slows up an hums replaced motor an capacitor took right off when it shuts down it won’t start back unless pressing contractors then it takes off but eventually motor comes to a crawl could it be fan relay or control board it’s a trane xl 1500 xi - On 2021-08-28 1 by Fred deel -

Reply by inspectapedia.com.moderator (mod)

@Fred deel,

As you replaced the motor and capacitor, I'd look next for a bad fan bearing that's binding and loading the motor, maybe worse when it's run for a while and is heated up.

Try the solution at

CAPACITORS for HARD STARTING MOTORS

 

Rental Unit A/C keeps shutting off, won't re-start for hours

Hi! I hope someone can help. For almost 2 years the unit in my rental shuts down after running and will not start back up for hours. They keep sending someone out and it fixes nothing. They've tried everything and can't figure it out. I'm getting sick of it. It happens during heating and cooling. Please help. thank you. - On 2021-08-23 by Giamatteo -

Reply by inspectapedia.com.moderator (mod) - check first for thermal overload

@Giamatteo,

I agree that what you describe is really frustrating and annoying. But I've very little to go-on here.

When an electric motor shuts off and won't re-start for hours I suspect first that an electric motor is overheating and being shut off on thermal overload. When the motor is hot it can indeed take several hours for it to cool down, its internal overload switch to reset, and then for the motor to re-start.

Thermal overload can be caused by low voltage, bad wiring, a bad motor bearing, etc.

Our most complete list of things to check for the air conditioner not starting problem that you described are given on the page above, better than I could type it a new here.

Please take a look, if you haven't already done so. It sounds as if you need an experienced Heating and AC refrigeration service technician on site.

Have you tried a conversation with the local A/C service company service-manager to ask for a senior technician.

Would you say AC and furnace shutting off I'm a little confused.

Are you saying that in heating mode and then cooling mode your system shuts down and stays down for a long.?

And are you saying and heating mode that happens even when the outdoor compressor condenser unit isn't running?

In other words are you running on some other heat sources such as gas or oil?

So you can see that from afar, without a bit more detail we're not sure just what equipment we're discussing.

If I were to GUESS that by "furnace" you're referring to the indoor air handler that blows both cool air in cooling mode and warm air in heating mode,
AND
if I were to GUESS that you're asking about a heat pump system that provides both heating and cooling,
THEN
I would ask if your investigators included, in troubleshooting, a shut down caused by high head pressure at the compressor that in turn can be caused when a refrigerant metering device like a capillary tube or a TEV (Thermostatic Expansion Valve) freezes up or clogs with debris.

I really want to be helpful but beyond this we know so little about your installation that I worry about wasting your time sending you off in wrong direction. \

Outdoor compressor won't run in COOL mode

If I switched to the Heat mode on thermostat control, the fan blower to blow air inside the house works fine on Auto/on selections. When I switched to A/C mode, the fan blower NOT working on Auto and On selections, but the compressor Fan and everything seems working fine outside the house, The furnace control board status lights "RED" (Normal).

Please help ! - On 2020-09-09 by PETER -

Reply by (mod)

Still this sounds like a control board problem to me, but I'd start by reviewing the thermostat wiring;

it's also diagnostic to note whether this is a new problem or is one that's been present since installation\

Sometimes my AC condenser unit will not turn on.

Sometimes my AC will not turn on. I have tried a number of things to troubleshoot this problem.

To be more specific my thermostat(s) will call for cooling, the (attic located) furnace blower will start but the condenser unit fan will not be running and the system will just circulate warm (ambient temperature) air.

The issue can be temporally resolved by removing power to the (attic) furnace and then connecting it again.

Unplugging the heater and plugging it back in. I typically accomplish this by flipping the furnace breaker in my electrical panel, though I have gone into the attic and simply unplugged the furnace from the electrical outlet just as a test.

After power cycling the furnace, the system will cool normally. That fix typically lasts about 24 hours before I have to power cycle the furnace again.

A couple years ago we had a problem with the system which turned out to be the Furnace Control Board. The technician that I called to come out fixed the board by reflowing the solder at one point on the board. A problem he had seen before. This fix worked. Thinking that this board was the source of my problems

I replaced the board with a new board from ICM Controls. This, unfortunately did not fix the problem.

After installing the new board everything was working normally, the test sequence worked as indicated, heating and cooling checked out when I set my stats for heat and then cool. After a period of time though, the same issue with the AC condenser fan not kicking on returned.

I inspected the electronics for the condensing unit yesterday and didn't see anything that stood out as a problem.

The capacitor is not bulging and everything appears to be connected properly. I even disconnected all the leads, applied dielectric grease to them and reconnected them. Still last night the problem returned. I tripped the breaker for the furnace and cooling resumed again.

I also have a zone controller in my attic. Two thermostats connect to the zone controller, zone controller connects to the furnace control board and drives two dampers in the ductwork to direct cooling to upstairs, downstairs or both. I see no signs of any issue with the zone controller.

I checked the LEDs on the zone controller while the AC was not working properly and found no fault or error indications. The zone controller is powered from a transformer inside the furnace so when power cycling the furnace, the zone controller is power cycled as well. I have not yet tried bypassing the zone controller. - On 2020-08-18 by Todd B. -

Reply by (mod)

Todd:

Have you done a detailed diagnostic of just where power is present or not?

At the control switch, at the board, at relays, etc.?

What about a slow-draining condensate pan and a condensate pan switch that shuts off the unit?

And incidentally, you can have a failed start capacitor that isn't bulged. It's pretty easy and inexpensive to try swapping in a new one.

 

Air Conditioner or Heat Pump won't start: Contactors won't pull in when they should

New package system a/s 10 ton first stage of cooling works perfectly when both stages of cooling are called for contactors will noy pull completly in .Yes good ground,208 330 yes 24 volts at transformer .Trane has no clue.

A/c contractors have no clue .

Installed new honeywell t stat in side pkg unit at factory wiring .Yes changed transformer yes have changed both contactors yed there is a matching unit next to this one both wired same other unit runs perfectly .Im at a total loss 30yrs exper s.O.S. Mp#3 954 -803- 1646 - On 2012-07-26 by Anonymous

If a Contactor is Not Pulling-In when it Should, Measured the voltage at the contactor

Have you measured the voltage at the contactor?

(Not at the transformer) With the contactor not pulling all the way in, it sounds like you don't have 24 VAC at the contactor.

If this
is the case,

check the connections between the transformer and contactor for a resistance
joint. Could be a wire-nut connection or the t-stat resistance (either via a relay or a
collector feed). - On 2012-08-03 by Coastal - H

Reply by (mod) - a bad connector or on occasion a partial short or leak in the low voltage wiring could drop the voltage at the contactor.

Coastal, thanks for that excellent suggestion made to Anon. It makes sense to me too that a bad connector or on occasion a partial short or leak in the low voltage wiring could drop the voltage at the contactor.

More diagnostics are

at COMPRESSOR START RELAY DOESN'T CLOSE

Daniel

Question: Heat pump worked on A/C but not on heat

My Bryant heat pump worked great all summer,

i switch it over to heat it came on for 1 second ,now it wont do any thing on heat or air ? -Wayne Bostian

Moderator reply:

Wayne

Let's start with the basics: has a breaker tripped or fuse blown? Is there power to the unit?

What came on for a second: the air handler indoors or the compressor/condenser unit outdoors?

 

Question: My Air Conditioner won't turn off - what to do?

Carla said: My outside air unit will not turn off on its own. I have to manually turn the breaker off to turn it off. Does anyone know why or how I can fix it?

Reply:

Carla if your A/C won't turn off it could be that the thermostat is set to a temperature that the system cannot reach - due to lost cooling or due to a setting below the capability of the system.

If your A/C won't turn off even if you set the thermostat to a temperature that is above the current room temp, then the thermostat or an A/C control board or switch is bad and needs replacement - in that case you need a service call from a trained HVAC Technician.

See OPERATING TEMPERATURES HVAC and

also CONTROLS & SWITCHES, A/C - HEAT PUMP

 

Question: first check circuit breaker if AC or heat pump won't start

My goodman CLJ30-1 ac wont turn on I have power to everything but nothing wants to come on curious if I should be getting any voltage readings of 220+- anywhere and if so where because I don't and what could be the possible problems keeping it from turning on - (Aug 23, 2014) Anonymous said:

My House has central air, this morning I try to turn down thermosat for the A/C to kick on, but nonething happened, I even try to turn the air conditioning cntrol switch to fan nonething. could it be that my a/c fuses are blown? (Aug 24, 2014) Dan Haney said:

Reply:

I'd start by checking the fuse or circuit breaker, then check for power at the unit

See AIR CONDITIONER WON'T START

Question: A/C or heat pump blower fan won't start

(Dec 13, 2014) Anonymous said:
I have a oil hot air furnace,the gun starts but blower won't come on,replaced blower control panel,need some advice,

Reply:

Anon if by gun you mean the oil burner and by blower you mean the air handler blower that moves building air through the ductwork those are of course different topics.

If the blower never comes on the limit switch on the furnace should turn OFF the oil burner.

If it doesn't SHUT DOWN the system immediately.

CHeck blower motor wiring and blower motor itself, as well as controlling relays.

 

Question: indoor air conditioning unit has no power and indoor and outdoor AC units won't start

(June 2, 2015) Bobby said:
The indoor unit has power to the furnace transformer and the transformer is producing around 27 vac but there is no power at the low voltage terminal block on the furnace circuit board. and neither the outdoor or indoor unit starts when called.

Reply:

Look for an open wire in the circuit or a blown fuse.

 

Question: A/C blower fan starts only if I spin it by hand

(June 4, 2015) Anonymous said:
Fan on my A/C unit won't start by itself, but if I turn on the unit and spin the fan by hand to start it, itwill run on it's own. What could be the problem?

Reply:

Anon: look for and replace the fan motor start/run capacitor.

 

Question: A/C not cooling after basement flooding

(June 30, 2015) Evelyn said:
Our basement took on water. The a/c quit working. Husband changed the fuse. Fan runs but no cool air.

Reply:

If the blower unit runs but there's no cool air most likely the problem is with

lost refrigerant

your outside compressor/condenser unit

or with a thermostat or control not set correctly indoors.

Ask your HVAC technician to include, in her diagnostics, a check for a control that got wet and was damaged.

 

Question: A/C compressor won't run after a power outage

(July 12, 2015) A/C Concern said:
My power went out the night before and now my outside compressor/condenser will not turn on. The unit turns on in the inside but it just blows hot air because of compressor/condenser will not turn on. What can be the problem?

Reply:

Check that you actually have power to all of the equipment; look for a blown fuse, tripped breaker.

(July 12, 2015) A/C Concern said:
Please disregard my last post. Something happened to our electricity and it was not producing enough electric to run the A/C. But now electricity is fine and A/C is working.

Question: heat pump stopped blowing cool air

(July 26, 2015) Bob said:
Twice this summer, the upstairs heat pump stopped blowing cool air (the fan continued to circulate air, and the thermostat remained on but the air would not reach set temperature), but the unit started working again fine the next day.

Both times we were dealing with a hot day (90-100, although other days this summer were also that hot). Is this off then on behavior symptomatic enough to diagnose the problem? Thanks.

Reply:

Bob

We need an onsite inspection and some tests to figure out what's happening with your system. It may be something as simple as a dirty air filter that causes the cooling coil to ice over when the system is working hardest.

 

Question: Rheem RANL-037JAZ won't start

Our A/C (Rheem RANL-037JAZ) was installed on 2011, each year we have less than 20 days to use it because it's not that hot here, but some times it worked fine, and more than half of the time it won't start, it made a clicking noise when I turned it on, and the fan spined a few turns then quieted down, it will try to turn on after a while.

The inside air blower always worked. I thought maybe it was the line voltage is too low, so I bought a Supco's SPP6E booster capacitor put in parallel with the run capacitor 43-101665-48, but it still didn't work.

I found the bottom of the run capacitor (the side with 3 terminals) is rusted, the whole thing is under the metal case cover, and the whole outside unit was under protecting cover too, I have no idea how that capacitor can get rusted, do you think that run capacitor is bad and even the booster can help, or is there any other reason? Thanks.

(Aug 4, 2015) P.H. said:

Reply:

Indeed a bad start/ run capacitor will prevent the system from starting. Typically you'll hear a start relay click and the compressor motor hums but doesn't run. LEAVE THE SYSTEM OFF until it's repaired lest you damage the equipment.

 

Question: heat pump won't start or run in A/C mode

(Aug 6, 2015) Gary said:
My heat pump will not run in A/C mode, but will run in heat mode. The inside blower will run. I swapped out the themostat from downstairs (same type-mercury swithches), still no A/C. Is there a fuse that may have blown?

(Aug 15, 2015) Ella said:

Turned on unit and nothing happens. Checked fuses, connections,wires.Don't know what the problem is so don't know if i could fix it myself or need to call someone. Senior, on fixed income. Help...

Reply:

Gary:

I suspect that the compressor/condenser is not starting and that in heat mode you're running on backup heat. If the motor never starts at all and if there is power to the unit, the problem is likely to be in a thermostat setting, a start relay or control board.

See DIAGNOSTIC GUIDE A/C or HEAT PUMP or

select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

 

Question: Haier Thermocool air conditioner won't run, green lights blink

My Haier thermocoool only shows the green lights/readers and then turns off tuns off immediately. What can be the cause?

16 Aug 2015 kinsey said:

Reply: contact information for Haier Thermocool air conditioners

Kinsey you don't give your location. As the diagnostic lights on your Haier Thermocool are not helping you I'd contact the company to ask their advice. If you're in NIgeria as I think from un published part of your comment, see

• HPZ Nigeria LTD. 45-47 Town Planning Way, Ilupeju Industrial Estate, Ilupeju Lagos Nigeria Thermocool customer service: 0 700 843 766 2665

...

...

Continue reading at  at AIR CONDITIONER WON'T START - topic home, diagnostic procedures, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see AIR CONDITIONER WON'T START FAQs-2 - more recent Q&A on air conditioners or heat pumps that won't turn on or won't run

Or see these

Air Conditioner or Heat Pump Won't Start or Won't Run Articles

• DIAGNOSTIC GUIDE A/C or HEAT PUMP
• COMPRESSOR / CONDENSER DIAGNOSTICS
• CONTROLS & SWITCHES, A/C - HEAT PUMP
• ELECTRIC MOTOR DIAGNOSTIC GUIDE

Suggested citation for this web page

AIR CONDITIONER WON'T START 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

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Comments & Questions are Welcome Here

If you posted comments here and no longer see what you wrote, please check for your comment in the Reader Q&A found above on this page.

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---