Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked. Air Conditioning & Heat Pump Compressor / Condenser Fan Inspection, Diagnosis & Repair
     


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

Air conditioning compressors overgrown with shrubs (C) Daniel Friedman

Article Contents

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.

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

Air conditioning condensing coil schematic (C) Carson Dunlop Associates

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.

List of Common Condenser Unit Fan Problems & Solutions

Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked.

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.

Also see Blower Fan No Start / No Stop

See INSPECTION CHECKLIST - OUTDOOR UNIT 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.

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. [Problems with the indoor A/C or furnace air handler fan are discussed separately at
BLOWER FAN CONTINUOUS OPERATION
and
at BLOWER FAN OPERATION & TESTING]

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.

Condenser fan blades loose, wobbling, bent

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 won't start

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. See CAPACITORS for HARD STARTING MOTORS.

Condenser fan runs but only intermittently and ha
s trouble starting

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

Condenser fan won't stop running

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

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

Condenser fan motor runs backwards

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 PRESSURE READINGS, COMPRESSOR 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.

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.

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?

Air conditioner or heat pump basic schematic (C) D FriedmanIn 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 shown below.

Suggested citation for this web page

FAN, COMPRESSOR/CONDENSER UNIT at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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