Fan on outdoor a/c unit not running

Check your o.d. unit to see if its running. If not check your breakers. Try turning tstat off and a few mins later turn it on and check to see if its running. If it is running, check for ice on the copper tubes that connect the indoor to the outdoor units. The large, insulated tube will freeze. You can look inside the o.d. to see any ice. If there is ice turn the cooling off and the fans' auto/on switch to the on position for a few hours. Check air filter and try to cool again. You may need to call for service if these don't work.

Your question does not include what type of system you are asking about, but the assumption is that it is a heat pump. The loud humming is the compressor running by itself while the fan is off.

This is the typical way a reasonably new heat pump operates:
There is a coil temperature sensor that initiates a defrost period to eliminate the frost/ice build up on the outdoor coil. In the defrost mode, the outdoor fan shuts off and the reversing valve in the heat pump reverses the direction of refrigerant flow to warm the outdoor coil. The same coil temperature sensor senses the temperature of the external surface of the coil and tells the defrost control when the frost is gone initiating another 'reverse cycle' to put it back into heating mode. In the heating mode, the outdoor fan runs again.

If you have the heat pump installed where snow drifts accumulate, you will have a problem extracting heat from the outdoor air, and coil frosting and freezing will be exaggerated. If you have excessive ice build up due to a defosting issue, the ice can actually stop the fan from rotating, but you would hear loud bangind and rattling for hours first as the fan blades come in contact with the ice.

If you do not have drifts, but continually have an excessive amount of ice build up, either the sensor is possibly faulty or the defrost control board is faulty. The sensor's clip could easily have been knocked loose from the coil by ice and is no longer sensing coil temperature and if so the result would be the lack of defrost initiation.

With the limited information i would suggest the following:
Check to see if the outdoor unit is running.
If the outdoor unit is running, grab the large copper line coming out of it and see if it is cool.
If the fan outside is running and the line is not cool then the compressor is not running or the system has lost its refrigerant charge.
Check these things and repost for a more complete answer.
Hope this helps.

Hi,
It is just coincidental that the fan motor died now...
Replace the condenser fan motor and you will be good again...

Here is a tip about troubleshooting your airconditioner...
There are many things that can cause your air conditioner not to cool...

AirConditioner Trouble - Review the Possibilities

heatman101

It sounds like you have a heat pump. When you first turn on the system the heat strips will come on and produce warm heat (referred to as supplemental heat strips), as temperatures rise the heat strips will turn off and the "A" coil will just exchange heat to maintain temperature thus conserving energy. . Initially the temps will be around 125 degrees at the register, and drop down to about 105 after the strips turn off.

On some TXV controlled outdoor condensing units the Thermostatic Expansion Valve will stick in the cool position and require replacement this will cause this symptom. It takes several hours to do and requires a licensed technician to do as it involves recovery of refrigerants. I hope this helps

Have them turn the outdoor unit off and wait a few minutes. When they turn it back on they should here
the fan and the compressor come on. They are to different sounds.

If they think that they have both come on, tell them to check the black insulated suction line. it should at least cold to the touch. If not it could be a freon issue.

If the line does get cold, have them checkthe filter in the house. If that is ok tell them to turn the power off
to the outside unit. Take a garden hose and wash
the outside coils on the outdoor unit,be carefull not to
smash the fins. Wash them at an angle from top to bottom.

Make sure the outside unit is running, compressor and fan. Sometimes it is hard to hear the compressor over the fan. If the outside unit is not working check circuit breakers first. Set thermostat to call for a/c and make sure the contactor in the outside unit pulls in. If it does check capacitor for whatever is not running. If everything seems to be running fine hold your hand above the fan outside. The air coming from it should be hotter than the outdoor air. If it isn't get the refrigerant charge checked.

Take the front cover off..
Inside you will see a barell fan..
Turn the unit on and give the fan a good spin by hand.. If it comes back on - the fan was stuck.. And is a sign of the fan motor on is way out - or maybe a bad capasitor.. If the fan does not come back on - the fan motor could be bad or maybe the capasitor..

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Is the outside unit running? if so can you feel warmer than outside air blowing from outside fan? If not your system may have a leak and pressures low. You can also check the piping to and from the unit larger one should be cold small one should be warm

You are going to have to increase the amount of heat absorbed by the evaporator coil on the indoor section of your system. First change the filter. Second turn the power off to the outdoor section and leave the indoor fan running until all the ice on the evaporator coil has thawed this could take a few hours. Third you need to verify that you are getting adequate airflow across the indoor evaporator coil and the outdoor condenser coil both fans should be spinning at full speed and airflow should be unobstructed by dirty coil fins or debris Hopefully after you've done this you will have cold air blowing inside and the larger of the two lines entering the unit outside will be cool to the touch but not frozen or even frosted regardless of run time and the small one should be the slightly warm but not hot. If the larger line continues to freeze then it could indicate a number of problems but essentially your condensers cooling capacity is outrunning your evaporator coils ability to absorb heat from air stream circulating in your home.Hope it works out for you GL!