Air Conditioning & Heat Pump Compressor / Condenser Fan

Inspect, Diagnose & Repair

What is the A/C or Heat Pump Compressor/Condenser Unit Fan?

The condenser unit fan is a blower that moves outdoor air across the condensing coil found in the outdoor compressor/condenser unit. The movement of outdoor air across the condensing coil transfers heat to outdoor air and allows high pressure/high temperature refrigerant inside the condensing coil to condense from a gas back to a liquid refrigerant.

The condenser fan is visible inside of the outdoor compressor/condenser unit such as the unit shown in our sketch at left, and in our other photos on this page.

Our central A.C. compressor sketch shows the condenser fan blades in the top of the unit (red line).

The green lines marks a common location for the fan control (at left) and more control circuitry (at right), and the blue line marks the fan motor itself.

Other compressor units such as those used

in SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS designs may mount the fan in a vertical position blowing out of the side of the compressor unit rather than out of the compressor top shown in our sketch.

If the condenser fan is running, you will see the fan blade spinning at speed (typically at 1725 rpm) and you will feel air blowing out of the unit.

Watch out: as we explain

at BURNED-OUT COMPRESSOR, if the condensing unit fan is not working, the compressor itself may shut down or even be ruined by overpressure or over temperature.

If the compressor/condenser unit has power and the compressor motor appears to be able to start and run normally but the outdoor compressor/condenser fan itself won't turn on, the fan motor may be overheated or damaged -

see MOTOR OVERLOAD RESET SWITCH.

Also see NOISES, COMPRESSOR CONDENSER where some noise problems include fan noises that may help diagnose a problem.

How the Air Conditioning Compressor/Condenser Fan Unit Works to Move Heat from Indoors to Outside

The air conditioner or heat pump condensing coil (shown at above)

receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state. Sketch from Carson Dunlop Associates, a Toronto home inspection, education, & report writing tool company [ carsondunlop.com ].

Typically refrigerant leaves the compressor and enters the outdoor condensing coil at about 100 psi and about 95 degF.

These pressures vary of course by type of refrigerant, ambient temperatures, compressor details, etc.

The Outdoor cooling fan (the subject of this article)

moves outdoor air across the condensing coil to cool it and assist in condensing the high pressure, high temperature refrigerant gas back into a liquid.

It is this process which completes the transfer of heat through the refrigerant from indoor air to outdoor air as the compressor/condenser unit compresses and then cools the refrigerant back to a liquid.

All of the above-listed air conditioner or heat pump components are discussed in detail throughout this website.

Common Condenser Unit Fan Problems & Solutions

• CONDENSER FAN WON'T START
• CONDENSER FAN RUNS SLOWLY
• CONDENSER FAN NOISES
• CONDENSER FAN WOBBLES
• CONDENSER FAN RUNS INTERMITTENTLY or SHORT CYCLES
• CONDENSER FAN WON'T STOP
• CONDENSER FAN RUNS BACKWARDS

Condenser fan won't start

Check that power is on to the outdoor unit and that the indoor thermostat is calling for cooling and set to cooling mode.

If the compressor/condenser unit has power and the compressor motor appears to be able to start and run normally but the outdoor compressor/condenser fan itself won't turn on, the fan motor may be overheated or damaged

See MOTOR OVERLOAD RESET SWITCH.

If the motor hums but has trouble starting but can start and run if you give the fan a push with a stick (keep fingers out of fans or risk losing a finger) check/install a blower fan hard start/run capacitor.

See CAPACITORS for HARD STARTING MOTORS

A condenser fan that won't start when power is turned on, but whose blades will spin easily when power is off may have a worn fan motor shaft bearing.

You may detect this by noticing that you can wobble the fan motor shaft (when power is OFF) or you may notice that you can pull the shaft in and out of the motor (loose end-play).

Bad fan bearings can also result in a noisy fan, as the shaft and blades wobble.

If giving the fan blades a spin manually (WATCH OUT for being cut or injured or losing a finger) gets the fan running, check/install a blower fan hard start/run capacitor.

See CAPACITORS for HARD STARTING MOTORS.

Outdoor condenser unit fan jerky, then stops completely

Reader question: At first outside AC runs but blower jerking back and forth and would not run. Then all of a sudden fan stopped jerking and does nothing and outside unit does not turn on.

What could have caused outside unit to stop working?

This is an old Frigidaire unit with variable speed motor. - CJ

Reply by moderator - What could have caused outside unit to stop working?

@CJ,

Check first for loose bolts or mounts at the fan, motor, or its blower unit cage.

Then check for a bad fan motor start capacitor.

Then check for a motor with a bad or seized bearing.

Don't confuse the outdoor condenser unit blower fan, discussed here, with the indoor air handler unit's blower fan that delivers conditioned air through the building's ductwork. Diagnostics for that fan are

at BLOWER FAN NO START / NO STOP

Condenser fan runs only at unusually slow speed

Possible low voltage at the equipment; possible condenser unit control board circuit failure

See CONTROL CIRCUIT BOARD, A/C for details.

Also possibly there may be no power to the fan and fan blades are moving due to local breeze blowing through the unit. On occasion a "slow" outdoor fan may be due to a fan blade that is not secured to the fan motor shaft.

Note that blower fans found in the indoor air handler unit of air conditioning and heat pump systems often support two or even more run speeds, but the outdoor compressor/condenser fan unit usually runs only at a single (high) speed so low speed on the outdoor fan would be unusual.

A slow condenser fan (or air handler unit fan) could be caused by a bad start-run capacitor.

Unfortunately this condition could indicate a burned-out A/C or heat pump compressor motor. If the compressor won't start and if the unit trips a breaker or blows a fuse as soon as it tries to turn on, the motor is burned out and shorted.

If the compressor/condenser unit is wired with 240V (or "220 volts") as most are, an overcurrent at compressor start-up may be tripping just one leg of a two-pole breaker or one of a pair of fuses, leaving the other circuit "live". This can leave the fan motor running.

A bad fan motor can also cause the fan to turn but only abnormally slowly. An internal short that is grounding the fan motor windings can leave the fan running, but abnormally slowly.

Condenser fan noises: ticking, buzzing, humming

Check for a fan blade hitting an obstruction in the unit; possible failing blower fan motor.

See details at HVAC FAN NOISES

Or see our encyclopedic list of

FAN NOISES in BUILDINGS

Or see TICKING NOISE DIAGNOSIS

Condenser fan motor buzzes or hums

If the fan itself is balanced and undamaged and secured to the shaft and the fan motor buzzes or hums the motor may be damaged, overheated, have an internal bearing failure, or the motor may be hard starting.

HVAC fan noises are discussed further

at HVAC FAN NOISES where we also refer readers to still more detail about hard-starting motors

and at

ELECTRIC MOTOR NOISE DIAGNOSIS for figuring out what may be wrong with the fan motor

Check/install a blower fan hard start/run capacitor. See the Capacitors link just below.

Condenser fan blades loose, wobbling, bent or loose

Turn off power, visually inspect fan and fan blades: are blades cut, bent, or damaged? Is the fan blade assembly secured to the fan motor shaft?

A bent condenser fan causes stress on the blower fan motor shaft and can destroy the motor. Minor bends can be corrected manually; damaged blades need to be replaced.

Condenser fan blades broken or come loose from the fan motor shaft

Turn off power and assure that the fan blade is secured to the fan motor shaft. If the fan spins on the motor shaft and the motor shaft won't turn the motor may be seized and need replacement.

If the fan motor is OK one or more allen screws set into the center bushing of the blower fan itself may need to be tightened to secure the blower fan to the motor shaft.

Condenser fan runs but only intermittently and has trouble starting

Check for loose wires or loose components on the fan unit control circuit board.

Short Cycling Condenser Fan or Condenser fan runs but keeps tripping its thermal overload switch and thus keeps shutting off

Typically this is caused by an internal short in the motor windings. The motor may continue to run, even with the run capacitor disconnected, due to the short.

Reader Question: when set to cooling the compressor fan stops and starts

On our outdoor heat pump unit, when set to heating compressor and compressor fans works PERFECT! But when set to cooling the compressor fan stops and starts, it will not stay on when compressor is on. I can hear the coil from the tinny fan control circuit board turning the fan off and then back on during this problem.

Fan is brand new. Capacitor is brand new. Fan control circuit board is brand new. Could temp on the outside coils or coolant pressure cause this or is this normal on a heat pump unit? (May 18, 2015) by Aubrey

Reply:

Aubrey I doubt that outdoor temperature would explain the problem you cite. More likely there is an electrical or control problem.

Reader follow-up:

We just talked to someone in person that has advanced knowledge of our problem and he said this is a normal built in feature and his unit does the same thing. Just sharing this info for others.

" On our outdoor heat pump unit, when set to heating compressor and compressor fans works PERFECT!

But when set to cooling the compressor fan stops and starts, it will not stay on when compressor is on. I can hear the coil from the tinny fan control circuit board turning the fan off and then back on during this problem.

Fan is brand new. Capacitor is brand new. Fan control circuit board is brand new. Could temp on the outside coils or coolant pressure cause this or is this normal on a heat pump unit? "

Reply:

Aubrey,

Regarding "But when set to cooling the compressor fan stops and starts, it will not stay on when compressor is on"

... it depends. Rapid fan on-off cycling certainly is likely to indicate an electrical or control problem worth investigating.

But it is indeed also normal for the fan on-off cycle to sometimes be different from the compressor motor on-off cycle. But it seems to me that that condition should not be for long. The compressor is depending on the fan to move air across the condensing coil to convert high pressure, high temperature gas back to a liquid refrigerant.

Follow up:

Correct. The fan does not stay off for a "long" time. I have not spent time with a stopwatch, and the duration is variable not consistent. But when it turns off it will come back on 1-3 min later (best guess)

Reply:

Your service tech will perhaps look for a bad control board, relay, or wiring connection or sensor.

Condenser Fan Won't Stop Running

The outdoor condenser unit fan may run for a brief while after the compressor motor has stopped but if the outdoor compressor motor itself has been off for 10 minutes or longer but the outdoor condenser unit fan never stops, check for a problem with the control board wiring or circuit.

Some of the diagnostics for the indoor air handler / blower fan can also help debug problems with the outdoor condenser unit fan.

So also see AIR HANDLER / BLOWER or FURNACE FAN WONT STOP - topic home

Also see AIR CONDITIONER / HEAT PUMP WON'T STOP

Condenser fan motor runs backwards

Could be a bad start-run capacitor or a bad control board.

See CAPACITORS for HARD STARTING MOTORS

A detailed case of diagnosing and fixing a condenser fan that was running backwards at speed changes is discussed below at

the FAQ's on COMPRESSOR / CONDENSER FANS

A Summary Checklist of Diagnostics for a Condenser Fan Unit that Stops Working

We list this sequence of condenser fan troubleshooting checkpoints roughly in the order that an experienced service technician will try them, putting easy, cheap, or more likely causes higher in the list. Contact us if you have suggestions.

• Power & Amps:
  
  Check that the system has electric power and normal voltages.
  
  Check the voltages: typically the fan expects to see 120V - is it seeing low voltage?
  
  Tripping circuit breakers can be an immediate indicator of overamping or drawing excessive current.
  
  Watch out: not always. Some problem circuit breakers may fail to trip when they should. Watch out - that's a fire hazard.
• Mechanical stoppage or resistance:
  
  Check for a mechanical obstruction (see photo at page top of a stick in the condensing fan) or for a fan bearing that is worn, sticking, freezing.
  
  Check also for a wobbly fan blade (worn or loose fan motor shaft or bearing) or for a fan blade that wobbles and hits the protective screening or for a fan that is jammed by an external occurrence such as a stick falling into the equipment.
• Capacitor:
  
  Check for a bad start/run capacitor if the fan circuit uses one.
  
  If the motor hums and does not start techs often try swapping in a new start capacitor.
  
  If spinning the fan manually will get it running, the problem is usually a bad starter capacitor.
• Fan Contactor Relay:
  
  Check for a fan contactor switch (also called the condenser fan motor relay) that is dirty, burned, or has loose connections
• Wiring damage:
  
  Check for nicked, cut, or corroded wires or wire connections between the fan motor and the fan contactor switch
• Seizing condenser fan motor or fan parts:
  
  Check for bad or loose fan drive shaft or worn, seized fan shaft bearings or for a binding fan motor drive shaft elsewhere in the assembly.
  
  Does the fan blade spin freely when the motor is off?
  
  A fan or motor drive shaft that is binding can kill or freeze the fan motor.
  
  A fan (or any electric) motor drive shaft that wobbles side to side (don't try this with power on) is worn out or has worn-out bearings.
  
  Also a fan whose blades are bent or damaged and out of balance can put a wobble on the motor shaft that leads to overheating and binding.
• Motor windings:
  
  Check for condenser fan motor windings or other wiring connections that open when the motor is spinning but close (and thus test "OK" when the motor is "off".
• Overheating fan motor:
  
  Check for a failing or overheating condenser fan motor - if the motor is running hot it may be failing internally (though low voltage, mechanical binding, or excessive current draw in the system can cause overheating too - is the motor stopping due to thermal overload?
  
  Airflow obstructions at the condenser unit can also cause the fan motor to overheat.
• Defrost cycle on heat pumps:
  
  Check that compressor motor itself is running.
  
  If the compressor keeps running and the fan re-starts after a 5-15 minute period, and if it's a heat pump running in cold weather, you may be simply seeing a defrost cycle.
  
  It is normal for the compressor to run with the fan "off" during a defrost cycle that might be 5-15 minutes depending on conditions.
  
  If the compressor and fan stop together (but the thermostat continues to call for cooling and the evaporator/cooling unit/blower assembly continues to run) there may be a refrigerant metering device problem, excessive head pressure in the system, or other related defects outlined beginning
  
  at COMPRESSOR / CONDENSER REPAIR.
• Check for a failed compressor defrost cycle timer 
  
  or control on heat pumps. If the defrost cycle sticks "on" or "off" in cold weather the heat pump will often stop working altogether.

This article series discusses the outdoor components of air conditioners and heat pumps: how the air conditioning compressor-condenser unit works; the detection of defects in air conditioning compressor and condensing units, including evaluation of air conditioner compressor noises, hard starting, lost cooling capacity, and detection of a burned out compressor or A/C compressors at or near end of their life.

If your air conditioning or heat pump system has lost its cooling capacity or won't start

see REPAIR GUIDE for AIR CONDITIONERS.

Which air conditioner, heat pump, or furnace fan is located where?

In our simple air conditioning (or heat pump) system sketch shown at left, the light blue fan shown at left in the sketch (above the red compressor box) is the outdoor compressor/condenser fan discussed

at FAN, COMPRESSOR / CONDENSER UNIT.

The dark blue fan shown at right in the sketch is the indoor air handler or blower compartment or cooling coil fan found inside the building. This fan blows building air across the evaporator coil (or cooling coil) to cool and dehumidify indoor building air.

We discuss this fan

at FAN, AIR HANDLER BLOWER UNIT.

Reader comments: important to use the right condenser fan motor start / run capacitor

Thanks for the great step by step instructions to troubleshooting. My AC unit is 18 years old, and I was afraid it was hopeless, but I decided to run through your checklist, and I was able to get it cleaned up and running again. (Aug 17, 2011) by Jim

I had a problem with my Condenser unit. The fan would run for a while then stop. I had a HVAC Repair company come out over 5 times trying to fix it. First the capacitor was replaced. The problem still came back in the mid day heat. Then they replaced the fan motor. The problem came back.

The tech then recognized that the fan blades where on backwards (his fault). The problem came back. Finally a senior tech came out and recognized that the fan required a different capacitor than what was initially changed in.

The final solution was for a separate capacitor that matched the fan's requirements to be installed.

Moral of the story: do it yourself and use the right capacitor. (Sept 19, 2012) by Robert

Reply:

Jim, thanks so much for the very nice feedback - that's just super. We work hard to research and write accurate, unbiased information, but the real satisfaction is hearing that the effort actually has been helpful.

Robert,

Thank you for the helpful comment. Indeed you point out that when replacing a start/run capacitor it is important to use the proper one.

HVAC Compressor-Condenser Fan Motor Replacement & Wiring

Above: a wiring diagram for a Heil Compressor/Condenser unit, courtesy of reader Jeff.

[Click to enlarge any image]

Watch out: the wiring instructions and diagram for your specific air conditioner or heat pump compressor/condenser unit are model dependent. The wiring diagram just above may not apply.

Question: my Heil Condenser unit with GE fan used 4 wires, new fan has only 3 wiers

I have a heat pump unit where the condenser fan motor has burned up. Ordered a new one off Amazon with the same CAP rating. My old fan was a 4 wire system and has a red,yellow, brown, and black wire.

The new motor is a 3 wire with yellow, brown, and black. I notice the red on the unit is coming off of a small circuit board that says low.

Am I able to wire a 3 wire fan into a heating pump that had a 4 wire fan?

Also, noticed the old fan wire actually has a quick connect coupler for all four wires to connect into a circuit board.

The brand of the Unit is Heil with a GE motor. (May 30, 2020) by Jeff

This Q&A were posted originally

at FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs

Moderator reply: start with the wiring diagram

Jeff

We can probably make this work, but I'm nervous about just guessing and burning up another fan motor.

See if you can find the wiring diagram for your condenser unit - often on a sticker in the unit, or always in the IO manual for the unit. We ought to be able to follow the old 4-wire fan wiring

Also some basic condenser unit wiring connections and wire color codes are summarized

at COMPRESSOR / CONDENSER DIAGNOSTICS

Reader follow up:

Sorry taken so log to reply, I work a lot of hours. I've included pictures of the schematic as you suggested.Really hoping this new fan is able to be used.

Mod reply:

Jeff

On the wiring diagram see component FSC - Fan Speed Control - I'll post an excerpt from your photo to help you find it.

That identifies what each of the wires are. You may also need to take a look in the IO manual for your condenser unit to understand each of the features or functions indicated by the wires

Follow up:

I see Red wire goes to LO for the fan.

The new 3 wire fan doesn't have this wire.

What would be the risk in not connecting the red wire to anything and just connecting the brown, black and yellow wires?

Reply:

My guess is no low speed, but we need to know all circumstances in which that speed is used to assure dropping it is ok.