Air Conditioner / Heat Pump Won't Start - Diagnostic FAQs

Diagnostic questions & answers on why the A/C or heat pump won't run
Air Handler / Blower won't start
Compressor / Condenser won't Start
Contactor Relay Repair
Heat or Cool works but not both
Heat pump won't start - intermittent
Switches for A/C or Heat Pump
Wiring damage

Switches that Can Turn off the A/C or Heat Pump Unit FAQs

Remember to check first for these common switches that will keep your air conditioner or heat pump from running:

• Condensate tray overflow switch detects condensate not draining - see CONDENSATE PAN SWITCH KEEPS AIR HANDLER OFF?
• Power switches to the indoor and outdoor equipment - see CONTROLS & SWITCHES, A/C - HEAT PUMP 
• Safety switches on blower compartment doors - see BLOWER DOOR SAFETY SWITCH
• Thermostat setting that is not calling for heating or cooling - see COOL OFF HEAT THERMOSTAT SWITCH and also FAN AUTO ON THERMOSTAT SWITCH

...

Air conditioner started up again after I unclogged its condensate drain system

Thanks for the tip about the condensate - I had quite a bit of water in the overflow pan and once I cleared it out the a/c unit worked again. On 2018-07-06 by Lloyd Hammond

Reply by (mod) -

So glad to hear it Lloyd.

For other readers: if the air conditioner or heat pump condensate drain system clogs not only is there risk of condensate water spilling into the building where it causes mold contamination or other costly damage, but also, if your system uses a condensate drain pan overflow switch that will turn OFF the system if the switch senses water where it doesn't belong.

Details are at CONDENSATE PAN SWITCH LOCKOUT

Clogged condensate drain turns off Heat Pump / Air Conditioner; do I need a new pan?

My Carrier heat pump A/C has stopped functioning. The repairman says that there is a condensate collection pan as a part of the indoor unit in the attic of the house and that a drainage line is plugged, and the rising water level in the pan actuates a switch shutting off the fan/compressor unit situated outside the house at grade level.

He says that the pan unit needs to be replaced at cost of about $400. Is this diagnosis credible? Any alternate diagnosis and remedies? On 2015-07-01 by NCK Bethesda Md

Reply by InternetLizard

+NCK Bethesda Md Can you try to find the drainage line and either clean or replace it? Sometimes there's also a pump that should be checked.

Reply by (mod)

It should not be necessary to replace an entire condensate drain pan simply to un-clog a clogged drain line. I'd want more explanation from that service tech before proceeding.

See CONDENSATE PAN SWITCH KEEPS AIR HANDLER OFF? - this or a door switch can keep the air handler "off"

High head pressure turns off our Condenser Unit

I had to replce both condenser fan motors because the bearings where to tight to spin freely.

What is happening now is that the unit is running for maybe 4 or 5 hours than both the first stage and the second stage compressers are tripping on high head pressure. What would you suggest to try. On 2012-07-18 by Terry

Reply by (mod) -

Terry the problem you describe is one I'd expect to turn over to a trained service tech - as I'm not sure myself what's happening. Often what's reported with high head pressure is a thermostatic expansion valve that is stuck shut or dirt clogged or frozen up.

Intermittent A/C or Heat Pump Won't Start FAQs

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 both 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. \

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.

Why won't the heat pump re-start and cool after it has run and then turned off?

My daughter has a mobile home that is 30 yrs old. The heat pump is used for both air conditioning and heating.

When the breaker is turned on, the air conditioning unit will run until it has reached the tempature set on the new thermostat. It will then turn off.

It will not restart when temp rises and outdoor section runs but no air is flowing through ducts.

What is causing this from not restarting and cooling properly? On 2016-09-13 by Doug Trombley

by (mod) -

Doug the problem is likely to be a control, a start capacitor, or the compressor motor itself, not the main breaker powering the unit.

See AIR CONDITIONER WON'T START - topic home

Heat Pump Cools down to Thermostat Set Temp but Compressor Won't Turn Back On

Trane Xl1600 heat pump cools down to set thermostat setting and then will not turn compressor back on and blow hot air in the home.

This seems to happen when Phoenix temperatures reach 100 degrees. Replaced both start and run capacitors a couple months ago as issue started last summer was working fine until 100 degrees. Any assistance with this would be greatly appreciated. On 2015-06-16 by Larry Trane

by (mod) -

Larry if replacing the start/run caps didn't fix the trouble I suspect either a failing control board / relay or a compressor motor that is failing beyond the ability of the starting cap to kick it off. Perhaps your tech will check the current draw of the various motors involved to see if that's going on.

by Larry - the capacitor is leaking oil

Noticed my run capacitor is leaking oil?

by (mod) -

Then it's shot and should be replaced.

Blower Fan motor cuts on and off on on hot days - in A/C mode

My inside unit is in a closet in the garage. On a hot day, fan cuts out for a minute or two and then turns back on. Is there a fan motor temp switch somewhere?

Or is it a sign of a future bad motor. During not so hot days, will not have a single problem . Thanks On 2016-07-14 by Bruce

by (mod) re: check for overheating fan motor

Bruce

Indeed some electric motors include an internal thermal overload switch.

Your HVAC tech might want to check the actual motor temperature against the data on the motor's data tag.

There you'll see the expected operating temperature range. If the motor's temp is within spec then there may be a failing bearing or a low voltage problem.

One of two furnace blowers will not start if second furnace blower is running.

I have a home zoned for 2 furnaces. The furnaces sit side by side and share a Healthy Climate Media Air Cleaner filter unit, ie the returns from both zones go through the filter unit and then into the furnace blowers which deliver the air to the appropriate zone.

The units are a Lennox G60UHV two speed and a G40UH single speed. Both units are on the same circuit and indeed plugged into a single duplex receptacle. The units were installed in about 2000 and have functioned perfectly until a few years ago.

At that time, first on a random basis and now more consistently the following symptom occurs: The larger unit and blower always works well and comes on when initiated by the thermostat for both heating and cooling.

The smaller unit works well when the larger unit is off. But, the smaller unit’s blower will not come on when the larger unit’s blower is on. Neither in AUTO or ON will the blower come on in full force, but it sometimes turns very slowly.

At this point it also turns on the air conditioning compressor. Other times the blower will not turn on at all, in this case the compressor usually does not come on. To get the smaller unit to work, I have to turn off the larger unit. Then the smaller unit’s fan will function normally.

Once it is on and up to speed, I can turn on the larger unit and it does not affect the smaller unit. But if the smaller unit should reach temperature and be turned off by the thermostat when the larger unit is on, it will not come on again until the larger unit is turned off.

From reading on line, I would guess that this is a starter capacitor problem. I suppose the easiest test would be to just replace the fan capacitor on the smaller unit and see if it then works normally. Any other suggestions would be appreciated. On 2016-06-28

by (mod)

One

You are describing a control or wiring problem that we can't debug by e-text; but an on-site experienced HVAC tech will be able to trace wiring and controls to see what's happening; There's most likely

- a control failure
- thermostat wires shorted
- a wiring error

- some odd combination of switch settings

Outside condenser unit not running but inside air handler is on after I replaced a capacitor

My inside unit responds to temperature setting and blower comes on blowing hot air.

Outdoor unit was not running yesterday when I noticed house not cooling.

I replaced the capacitor this morning and unit was working fine. It started warming up in the house again.

Inside blower unit is still working but outside unit is not working again. Fan moves freely in either direction.

Bad new capacitor? On 2012-06-30 by Jim

Reply by Mod

Jim: I suspect that you have a bad fan motor that couldn't be "fixed" by replacing the capacitor.

First confirm that your wiring was correct, then try checkning the motor itself.

Intermittent blower fan intermittent failure diagnosis

I have a packaged unit air conditioner. The circulating fan is failing to operate at random times.

In an attempt to solve the problem, I have replaced the contact switch and capacitor.

The air filter is clean. I have taken the circulating fan motor out and had it bench tested.

It tested OK. The thermostat works normally.

The air conditioner cools the house well during the times that it is not failing.

The compressor fan continues to work at the times when the circulating fan fails.

There seems to be no consistent reason for the failure, as in the outdoor temperature can be hot or cool, or the machine may work normally for only 2 hours or over 24 hours.

Can anyone tell me what the problem might be, or tell me what I should try next to solve this strange problem? Any help will be appreciated. On 2011-09-06 by Amie West

by (mod) - fan controller problem

Amie

It sounds as if you could have a fan controller problem; some A/C units include controls to vary the fan speed or even turn it off; or a wiring problem, even a loose connection;

I'd review all of the wiring connections carefully for soundness and then perhaps give the manufacturer a call - for your unit model number a service department tech may know exactly what's happenbing.

Keep us posted - it'll help other readers;

by Amie West

I appreciate any idea, thanks. I have checked all the connections for continuity, but calling the manufacturer is a good idea.

I hate to call a repair man for something that I could do myself, this is just so unusual that it is hard to diagnos. I'll let you know, but if anyone else reads this and has an idea, I'd love to hear it.

Unit Runs in Heat or Cool but Not Both Modes FAQs

System runs in HEAT but 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.

Consider that if your system is a heat pump, even though your indoor unit seems to run in HEAT mode it may be that it's running in backup heat moder and not requiring the outdoor compressor/condenser unit.

Heat pump won't start or run in A/C mode but runs in HEAT mode

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 6, 2015) Gary

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. (Aug 15, 2015) Ella

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.

Heat pump worked in Air Conditioning mode but not in HEAT mode

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?

Heat Pump Works Only in Cooling Mode, it Won't Heat

My heat pump runs when calling for cooling, but when calling for heat it won't run ,the Aux comes on On 2015-09-25 17:16:19.990602 by George

Reply by (mod) -

George,

I suspect that either the outdoor temperature is below the cut-in temperature for your heat pump or there is a bad control board, relay, or temperature sensor.

Air Handler Blower Won't Start or Won't Keep Running FAQs

After a Repair Job the AC will not turn ON

Hi. Neither the inside nor the outside unit will come on. We’ve changed out the thermostat. Any idea what else we can do?

Our repairman had it running and then it stopped. When he came out, the outside unit wouldn’t go off with us turning it off at the breaker.

He replaced a part to help with that. Now this new problem.

Oh and the thermostat will go blank without batteries. It had stopped doing that too. On 2019-04-30 by Alice

I meant to say it wouldn’t go off without us turning it off at the breaker.

by (mod) -

Since usually the thermostat is getting its power from a low voltage (24VAC) transformer that is powered by the air conditioner or heater's indoor unit main power circuit and switch, if power is off to your indoor air handler, air conditioner, heat pump or furnace, the thermostat will also go blank.

If you confirm that power is ON at the indoor equipment and the thermostat is still blank, ask your technician to check and eliminate any possibility of a problem with the thermostat wires themselves.

Less often the thermostat iteslf has failed.

A/C blower fan starts only if I spin it by hand - bad motor capacitor?

Reply:

Anon:

When the blower unit fan OR the condenser unit fan will run after you give it a starting "spin" it's time to look for and replace the fan motor start/run capacitor. - mod

See diagnostic details

at BLOWER FAN WONT START

and then

FAN MOTOR START CAPACITORS

Blower fan motor won't start: What are the symptoms of a bad start capacitor?

Thanks for all the great information! What are the symptoms of a bad capacitor? On 2012-06-18 by Jerry

by (mod)

Jerry,

An electric motor that hums and won't start might need a new start capacitor.

An electic motor that runs but never gets up to full speed may need a new run capacitor.

You might actually see a bad capacitor - if it or its wires look burned or if the unit has swollen or cracked. But more often the symptom is that the electric motor the cap is supposed to support is having trouble starting or wont' start or won't run.

A capacitor that is visibly burned, leaking, coated with white crust, or otherwise damaged is probably bad and needs replacement.

Check out

• CAPACITORS for HARD STARTING MOTORS and also
• TEST a MOTOR START or RUN CAPACITOR  where we explain how to test and replace a bad start/run capacitor.

Air Handler Blower won't start - traced to bad control board

My Trane compressor kicks on, but yesterday the blower motor did not - it seemed to have no power to it. I called a reputable A/C company in town.

The tech did something to the capacitor and said it was ok – he said he jiggled it. Checked the compressor, said it was good as well. He then said he was going to bypass the board and see if it was the blower motor relay that is part of the board.

After moving some wires, with the compressor on, the blower motor came on.

He told me the board had to be replaced, and cost before tax was around $1,300. Was this an accurate diagnosis? And the capacitor, was that accurate as well? What exactly did he do? Can I hook up the blower motor? We are used to having the fan on all the time while we are home.

Thanks for your time and consideration. On 2012-06-17 by Jerry

by (mod) -

Jerry

See BLOWER FAN OPERATION & TESTING to diagnose your A/C blower problem.

Jiggling the start/run capacitor might find a bad connection, but I'm not sure how jiggling a capacitor tests for a failed capacitor itself. Sometimes we can see a bad cap by visual inspection but usually the tech will test the device.

Having no power at the air handler - I'd expect the tech to start at the main electric panel and trace wiring forward to the unit to be sure power is being delivered, and then that the TT is properly set (sounds like it is), and that the controls or switches or circuit board at the air handler are trying to turn it on.

If so, then look for a bad motor or start cap.

So tracing a problem to a circuit board is plausible. If your unit is only A/C it might make sense to double check that capacitor and any relays or switches.

There are more switches to double-check such as a bad blower compartment door safety switch, or the door ajar, or even a wet condensate overflow pan (and a sensor switch there) can prevent the blower from starting.

If the tech performed a specific test on the circuit board and found it defective, that is of course credible.

If your unit also provides heat you may have a separate fan limit switch with a manual fan-on control, or you may be able to turn fan to constant on at your thermostat.

See if those are present - if you can run the fan then we know the problem is not fan motor nor start cap for that fan.

Furnace blower fan won't start after replacing air handler blower control board

I have a oil hot air furnace,

the gun starts but blower won't come on,

replaced blower control panel, need some advice, Anonymous

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.

I suspect the the blower motor itself or its start capacitor is bad.

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

Blower Won't Start: Is the blower motor RESET SWITCH ? Check the capacitor?

There is not a reset switch on my blower motor. Do you think it is a bad capacitor keeping the fan from running? - June 15, 2011 Jeff 

Reply:

Jeff:
Indeed many electric motors do not have a manually resettable overload reset switch ( ELECTRIC MOTOR OVERLOAD RESET ) ;

If one of these motors won't start, and presuming that there is power to the unit and all else is operating normally, I'd suspect a bad capacitor or a bad motor itself. If you can spin the motor manually (with the power off so as not to get injured) then it sounds as if it's not seized and I'd try a new capacitor.

Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE

and CAPACITORS for HARD STARTING MOTORS

(June 16, 2011) Jeff 

Thanks! I will call a AC tech for that but I will suggest that to them. Thanks for the very informative site and the feedback.

Where is the blower fan reset button on my heat pump?

No blower fan reset button on my heatpump. How so I reset it? On 2017-05-27 by percy

by (mod) - No blower fan reset button on my heatpump

IF the motor has an internal thermal overload protection it will self-reset after the motor has cooled down. Leave power off for 15 minutes or longer.

If the motor has voltage delivered at its terminals and doesn't run after that, the motor is shot and needs replacement.

Central Air Conditioning Blower Fan gets Hot and Stops

My central air unit is outside. it is 30 years old. The fan gets hot and stops.

After it cools down it will start up again.

I had new fan installed and it does the same thing. The fan just hums after about 10 minutes of cooling. Where do I start or should I just look for new unit? (July 29, 2011) Barbara

Reply:

Barbara it's odd that a new fan motor would overheat and stop running unless

- the temperature is actually within normal operating range and it's a start/run capacitor that's failing

- there is a wiring or other problem causing abnormal overheating.

Are you sure it's just the fan motor and not the compressor that's overheating?

Blower won't start but diagnostic lights say it's running

Have a blower motor that won't start.

1) Ran 120 VAC to connections on motor, motor spins up fine.

2) Pulled the controller board, thinking that this must be the problem, after looking at the Board diags, wasn't sure and put it back.

3) After installing the controller board, 2 slow blinking lights which diags say indicates it is on. (Motor still won't start)

4) Checked Drain Pan - Empty, checked the line, no blockage.

5) Cleaned Filter

Not sure where to go from here.

Any thoughts?

Thanks On 2017-06-12 by George

by (mod) -

George,

Also check for a bad door safety interlock switch on the access compartment door to the blower.

Air handler turns on but fan buzzes & won't run

SC unit turns on... fan will not blow, hear a buzzing sound On 2012-09-14 by Ray

Air blower makes a humming noise and won't start - jumped R & G Terminals on the control board

Carrier A/C when selecting thermostat to cool with fan ON or Auto, outside compressor runs OK, steady red fault light on control board,

Air blower will make humming noise but will not start, I jumped R and G at both the board and thermostat but blower still wont start, could it be a faulty capacitor or possibly faulty relay on cont. board.

Help is appreciated. On 2012-07-18 by Mario

by (mod) - check for bad fan bearing, siezed motor, then go to electric motor diagnostics

Ray

Check first for loose or burning wires and connectors - as there would be a safety concern involved.

Check for a bad start/run capacitor on the fan motor

or for a bad motor - some diagnostics are

at ELECTRIC MOTOR DIAGNOSTIC GUIDE 

Mario,

"humming or buzzing noise but will not start" usually means a bad motor or (check first) a bad start/run capacitor.

But first with power off see that the motor and fan spin freely - that there is no siezed motor or fan bearing.

Air Handler Blower Unit Won't Run

Our central AC's blower motor is not coming on. Condensor turns on and I can see it's fan is running and one line starts ice on it. Please help On 2011-07-18 by Nancy

by (mod) -

First: If your indoor air handler fan won't run and the thermostat is calling for cooling and the outside compressor is starting up normally, check for lost power or power off at the indoor unit; check for a fan motor reset button popped out; check for a blower fan driven by a pulley and belt with a lost, loose, or broken fan belt;

Then: Nancy if the outside compressor/condenser runs and the inside A/C blower won't, after checking for power at the blower unit (air handler) (and there may be more than one off switch, including a condensate drip tray overflow switch), anyway after checking that there's power and all of the switches are on I'd check that the blower fan motor has not gone off on reset (or that the motor is running but a belt is broken inside the fan unit if yours is a pulley -driven unit.

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

Reply:

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

Outside unit runs, inside unit won't turn on except in manual FAN ON

My outside ac unit will turn on, but the fan inside will not blow air through the vents.

But if I turn the ac to the off position, and the fan to "on" instead of auto, the fan will start blowing air.

It is like I can either use the fan or use the ac unit, but not both of them On 2011-08-15 by clexow

by (mod) - Turning on the blower manually keeps it running

When you turn off your A/C and switch the fan to "ON" you are manually turning on the indoor blower assembly fan itself, independent of the A/C system.

On the thermostat if you set the appropriate switch to "COOL" that turns on your A/C system and the fan will run automatically under control of the thermostat and additional control circuits in the air handler and in concert with the outdoor compressor/condenser unit. Normally if a thermostat has the necessary switches and it's wired correctly, you could set the TT for COOL and ALSO set the fan either to AUTO or to ON. in "ON" position that forces the fan to run continuously regardless of whether or not the TT is calling for cooling.

But you're not seeing that.

When you turn on the A/C at the TT but you are not getting cooling, either a service or control switch is OFF at your equipment (or in the main electric panel) or a thermal overload reset switch has turned off the equipment, or a motor such as a compressor motor has seized.

I'd start by going through the LOST COOLING CAPACITY diagnostic steps to be sure everything is turned 'on', and if that doesn't help you probably need an HVAC tech service call.

Goodman Janitrol unit fan makes buzzing sound and doesn't spin

My Goodman Janitrol 2 ton turns on but the fan just makes a "buzzing" sound instead of spinning. - On 2011-06-05 by Jeff - J

Moderator reply: If your A/C is buzzing

Your fan motor may be shot or there can be a control board problem - the service tech might first try replacing the fan motor capacitor(s).

If your A/C fan is buzzing but not spinning my first guess would be that the motor is burned up or perhaps easier, the motor needs a starting or start/run capacitor.

Check out the article titled CAPACITORS for HARD STARTING MOTORS 

Indoor blower fan motor won't run

I have a Rheem RHSLHM3017JA The indoor fan motor will not stay on.

Replaced fan motor and T Stat. On 2017-06-05 by Rick

Reply by (mod) -

There are several possible problems. Check these diagnostic articles:

• BLOWER FAN WON'T RUN in AUTO - COOL
• BLOWER FAN WON'T RUN in AUTO - HEAT
• BLOWER FAN WONT START
• BLOWER FAN WON'T START, BUZZING

The blower motor in my air conditioner air handler won't start

The blower motor in ac air handler won't turn on - On 2017-10-23 by Jan

by (mod) - The blower motor in ac air handler won't turn on

Jan

at FAN, AIR HANDLER BLOWER UNIT we give diagnostic steps to check when the air handler blower won't run. Try that and let me know what questions remain.

If your air handle is for BOTH heating and cooling, then also see FURNACE FAN WONT START at https://inspectapedia.com/heat/Blower-Fan-Wont-Start.php

Why would the air handler blower refuse to run unless we open the cabinet doors?

What cause a fresh air unit aircon to cut off when the doors are closed but switches on again when the door is wide open but after sometime it overheats.this is very confusing because there are no limit switches or sensors on the doors becauce i would suspecr maybe they might be faulty - On 2017-06-21 by Vusi

Why might air handler blower stay off ?

by (mod) - are you sure there's no door interlock switch?

Perhaps a faulty door safety Interlock switch - I'd check that the unit has power, that the door interlock switch is working properly, and that there are no loose connections.

Should I turn off the unit at the thermostat if the air handler blower has failed?

if the blower fan motor of my central air conditioner unit stop working should i turn off the unit from the thermostat and for the air handler as well. 2017-05-23 by Anonymous

Reply:

Anon

Turning off the air handler at the thermostat may make some sense as running the air handler when the compressor/condenser isn't working won't provide cooling.

You can move the thermostat A/C control to OFF, or you could accomplish the same thing by simply setting the thermostat temperature well above room temperature.

Alternatively you could turn the cooling OFF but if your thermostat (or air handler limit control) has a FAN ON or MAN switch position you could continue to circulate indoor air as well as filter it - that might provide a little comfort even when the cooling system is not working.

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

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

Can I install a larger fan motor on my air conditioner to fix a fan problem?

Can a larger fan motor (1075 1/2 hp) be used to replace this 1/3 hp 825 . I serm to be having problems with fan.

If motor is bad. I may need it replaced. The service co. Has the larger motor avail. Or I need to order one.

The 825 is less common and I may have an isdue waiting to get that esp. Now n amazon will be halting shipping. - On 2020-04-13 by karmika1586

Reply by (mod) - don't try that without proper diagnosis first

Karm

Watch out: I would not try to fix a fan no-start problem with a larger fan motor, because the underlying problem remains. I'd look for the trouble source:

• bad wiring
• bad control or control relay
• bad start/run cap (or mistake when installing new one)
• failing fan motor
• low voltage

and other diagnostics in the articles I suggested.

Blower fan won't start - we took out the air filter

My blower fan will not start. Really need to know if by any chance it may have to do with the fact that we removed the filter because it was dirty and we didn't have a new one to put in right away and that's when the unit stopped!

Can something happen to make it stop due to no filter?

Please help. Trying to fix it ourselves.

We were going to replace the motor in the fan unit of the a or handler. It won't start. Very nervous because it's July4th in South Carolina! On 2017-07-04 by Ellen M Ames

by (mod) re: will removing the air filter damage the blower fan?

Ellen:

Removing an air filter itself wouldn't damage the blower fan,

BUT if the filter was in the blower compartment and you had to open a compartment door to remove the filter, then a safety door interlock switch could be open - thinking the door is not fully shut - keeping the fan off for safety. ,

Check that out and let me know what you find.

Watch out: running an HVAC system with no air filter will cause dust and dirt clogging of the blower fan itself and may harm other components.

See our detailed diagnosis and repair procedure at

BLOWER FAN OPERATION & TESTING

Air handler won't keep running; evaporator fan keeps running, gets hot, turns off

The outside condenser is working fine but the indoor evaporator fan will not stay running.

It will run for about a minute and gets very hot and turns off. I have repalced the capacitor and not help, and ideas? - Jason

Reply:

It could be a control board or fan relay problem but most-often when the indoor blower fan will start but won't continue to run I suspect either a failing fan motor (it's overheating and jamming or stopping) or a bad fan motor run capacitor. . I'd ask for a service call. Let us know what you found - it may help other readers.

See the diagnostic article found at FAN WONT STOP - LIMIT SWITCH

Generally, when your indoor blower compartment fan is overhreating it sounds as if the motor or a bearing may be failing.

Often a failing electric motor produces an early warning when its starter capacitor fails repeatedly. If you are qualified and can do so safely, check the amperage draw against the motor's data plate specs. Watch out: electrocution hazards.

If an A/C unit won't turn off start by setting the thermostat set temperature to well above the room temp - satisfying the thermostat.

If the equipment still won't turn off either someone left the fan switch in manual "on" or there is a control or board problem that needs to be repaired - in that case I'd shut off the equipment and call my service company.

Carrier Infinity ECM Blower Fan Motor Won't Run

I am having a problem with a carrier infinity ecm blower.

Weather I have a call for heat, cool, or just the fan, the fan gets two or 3 rotations in before it stops. Then about a minute later it does the same thing. I am trying to diagnose this issue as my coil has frozen up now - 2018-08-28 by Thomas M -

by (mod) -

Thomas

Let's start with the diagnostic suggestions at FURNACE FAN WONT START https://inspectapedia.com/heat/Blower-Fan-Wont-Start.php

I suspect a bad capacitor or a loose wire or connection.

by Thomas

no lose wires checked them all. No capacitor has a wiring harness. There was a good amount of water in the blower wheel so i think it might have slung water around and got somethkng wet. The borad is dry as a bone and no burn marks present

by (mod) -

Sounds as if something may be water damaged; a bad bearing, bad relay. If (without getting shocked or losing fingers) you give the fan a spin will it start and keep running?

A tech would be checking voltage at the motor terminals and if the motor, perhaps taken out and bench-tested, doesn't run then she'd follow procedures

at ELECTRIC MOTOR DIAGNOSTIC GUIDE

or would replace the motor.

by Thomas M

i did that and it did the same thing just a few rotations and repeats. I really dont want to be wrong and throw parts at this and waste more money. And thank you for taking time out of your day to assist me

A/C Blower won't work on AUTO-HEAT but runs on MANUAL

We have a heat pump and recently the blower motor would not come on when the pump would start up.

I've been able to get the blower to come on by switching the setting on the Tstat to manual so I know that the blower itself is fine, what should I check next and where should I look for these parts to check?

A large capacitor was replaced 4 years ago along with a wildly overpriced board about the size of an old school paper flashcard you would use in school for studying.

I want to add that thanks to abnormally warm weather this weekend I was able to turn on the A/C and during this time the blower motor would kick on when set to automatic on the thermostat.

So at this point the blower will not work under auto when set to heat and has to be set to manual to run.

Wouldn't the run start capacitor be required under A/C as well? This makes me think that the thermostat could have failed or been knocked off the wall by my kid again. On 2018-02-27 by BillTheWelder -

by (mod) -

Yes you are quite right, Bill.

The fan doesn't know what sort of air it's blowing - cold, or hot like some of my explanations.

It's a fan limit switch and a control board that wants to turn the fan on at the right time in cooling and heating mode.

So in heating mode, for example (hot air), if the heat is not working, the plenum never heats up and the blower won't turn on. The fan limit switch doesn't want to blow cold air on to occupants who were hoping for heat.

Air Handler Blower fan starts, runs briefly, stops - won't keep running

Air handler fan starts then stops a few seconds later while the rest of ac system continues to run On 2017-07-09 by Darin

by (mod)

I would check for these things in this order:

1. an obstruction blocking the fan,
2. an overheating fan motor,
3. a loose or corroded wire connection,
4. a loose or faulty blower door switch,
5. a bad control board relay, or a bad start/run capacitor

and if none of those seem to be the obvious problem that I would look at the additional Diagnostics in this article

FURNACE FAN WONT START

Sorry I can't pin it down more narrowly but I just don't know enough about your situation

Blower shuts off after 30 seconds

Blower Motor shuts off after 60 seconds:
I have an older Trane gas furnace / central AC unit. Cleaned the AC coils (outside) yesterday and turn on AC today. Started fine, but after 60 second, blower (inside) shut off, but outside unit continued to run.

Trouble shooting steps I've taken:

1. Turned Fan ON at thermostat - fan/blower ran 60 seconds, then shut off
   
2. Jumpered Fan ON (thermostate wires R to G) - fan ran 60 seconds, then shut off
   
3. Turned on AC - outside unit and fan came on, but fan shut off after 60 seconds, outside unit ran
   
4. Turned on Heat - heat functions worked normally...burner heats, fan on, at temp burner off, fan off after delay.

Any suggestions on what is shutting down the fan after 60 seconds? - BErik

Reply:

Berik, if you are in heating mode watch the fan limit control switch. If the heater is shutting off at the upper safety limit then air flow is probably blocked, causing overheating.

If you are in cooling mode I wonder if your system has emergenc heaters running.

BErick

Looked at this some more. New blower motor replaced in the winter works fine in Med-High speed, but for A/C and Fan-ON motor is on HIGH and seems to be shutting down...I assume on over-temp. Air flow seems good, over temp shut down even when panels off the furnace. I will look at wiring, voltage next.

(mod)

Good progress. If you can safely measure current draw that'd be helpful.

BErick

I currently have the furnace-side High connected to the blower-motor Med-High wire, like when the heat was on. Operation in the lower speed is working. I was able to measure current draw. The motor is an Emerson M55HXHKP-9722, 115V 14 Amp. Using amp meter, got the following readings: High - 18-20 Amps, Med-High - 14 Amps, Med-Low 10 Amps.

I know the motor should not draw 18A on High, based on its rating. Do you think this means the motor is bad or has failed?
Thanks.

(mod) said: Yes BE.

Running the blower fan with A/C off - the fan stops.

We often run our HVAC fan w/o turning on the a/c.

Fan stopped operating, so I have replaced capacitor, motor, fan limit switch and control board.

The fan comes on but shuts off after a few minutes of operation. What is wrong? On 2021-08-06 by Dave G

Reply by inspectapedia.com.moderator (mod)

@Dave G,

Could be low voltage, a wiring error, a failing bearing in the motor or in the fan that the motor drives, causing overheating and thermal cut-off.

If you're confident that the wiring is correct you might look - with power off so you don't get a finger chopped off- more-closely at the blower assembly to see that the blower fan itself spins freely and without wobble.

Then

Take a look at

ELECTRIC MOTOR DIAGNOSTIC GUIDE

Blower Fan Won't Keep Running

The blower on our furnace is set to run continuously. Lately it starts and then runs a few minutes or sometimes seconds and then completely turns off.

This happens in the evening hours when the temperature in the house is higher than what is set on the thermostat. We have had two furnace guys look at and they don't know what is wrong. To be fair, it wasn't turning on and off and on when they were here. On 2019-04-12 by Carol

by (mod) - blower set to run continuously is shutting off

Carol

IF no one changed the switch to keep the fan on continuously and now it's running intermittently I'd think that there is a loose or corroded wiring connection, or a failing limit control, or a failing blower motor.

Which switch is set "ON" - at the fan limit controller? or at the thermostat? That tells your tech where to start checking wiring.

Damaged Air Conditioner or Heat Pump Wiring FAQs

Moved to DAMAGED A/C or HEAT PUMP WIRING FAQs

A/C or Heat Pump Outdoor Compressor/Condenser Unit Won't Start / Won't Run FAQs

Moved to COMPRESSOR / CONDENSER UNIT WON'T START or WON'T RUN FAQs