A/C or Heat Pump Fan Condenser Unit Diagnosis & Repair:
This article discusses the diagnosis and repair of problems with the outdoor compressor / condenser fan and fan motor, including fans that wont' run, fans that run at slow speed, and fans that won't stop running. Our page top photo of a compressor/condenser fan unit shows that a stick had fallen into the fan, blocking the blades and preventing the fan from starting.
A simple problem like this can also burn out a fan motor. Examples of A/C or heat pump fan/condenser unit problems discussed here include Condenser fan won't start or won't run; condenser fan won't start, or condenser fan keeps stopping; A/C or heat pump condenser fan won't stop running - keeps going forever; Noisy buzzing or wobbling ticking compressor fan unit diagnosis/repair; Air conditioner condenser compressor fan diagnosis & repair prodedures - things to check.
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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, an in our other photos on this page. Our central A.C. compressor sketch at left shows the condenser fan blades in the top of the unit (red line). The green line marks a common location for the fan control circuitry, and the blue line marks the fan motor.
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.
The air conditioner or heat pump condensing coil (shown at left) receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state. Sketch from Carson Dunlop Associates.
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 using the links at the left of these pages.
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.
Also see Blower Fan No Start / No Stop
See COMPRESSOR / CONDENSER INSPECTION CHECKLIST for a simple checklist for the outdoor compressor/condenser unit. Initial, simple diagnostic checks of the air conditioning compressor are also described
at Compressor failure diagnosis.
If the condenser unit fan won't start at all, check for power to the unit and to the fan motor and that all of the controls are calling for cooling (or heat pump operation); check for loose, disconnected wires; Check for a frozen fan motor (motor won't turn manually when power is off). 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.
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.
Check for a fan blade hitting an obstruction in the unit; possible failing blower fan motor.
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. Check/install a blower fan hard start/run capacitor. See the Capacitors link just below
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.
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.
Check for loose wires or loose components on the fan unit control circuit board.
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: (May 18, 2015) Aubrey said: 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?
Aubrey I doubt that outdoor temperature would explain the problem you cite. More likely there is an electrical or control problem.
(May 19, 2015) Anonymous said:
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? "
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.
(May 20, 2015) Aubrey said:
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)
Your service tech will perhaps look for a bad control board, relay, or wiring connection or sensor.
A blower fan may run for a brief while after the compressor motor has stopped but if the outdoor fan never stops check for a problem with the control board wiring or circuit. Also
see Blower Fan No Start / No Stop
Could be a bad start-run capacitoror 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 section on Questions & Answers about compressor/condenser unit fans.
At REFRIGERANT PRESSURE READINGS we discuss other backwards-running electric motors including some types of air conditioner or heat pump compressors and even well pumps.
Also see BLOWER FAN OPERATION & TESTING.
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.
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.
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.
In a warm air heating system that does not include air conditioning as well, the indoor fan is still located in the indoor air handler and is discussed
at FAN, AIR HANDLER BLOWER UNIT.
Continue reading at CAPACITORS for HARD STARTING MOTORS or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Or see FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs for diagnostic questions that can help get the condenser fan working.
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OR use the Search Box found below at Ask a Question or Search InspectApedia
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Please see the separate collection of diagnostic questions found at FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs
(Aug 17, 2011) Jim said:
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.
(Sept 19, 2012) Robert said:
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.
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.
Thank you for the helpful comment. Indeed you point out that when replacing a start/run capacitor itnisnimportant to use the proper one.
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