A/C Not working... Outside Fan Running, inside Fan not

Old 08-08-11, 11:16 AM
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A/C Not working... Outside Fan Running, inside Fan not


My A?C is not working at the moment. It has intermittently stopped pushing cold air throughout the house for the last month or so, but always came back on so I didnt worry too much. Today it will not blow air at all. I turned the tstat to the on position and went and checked the outside fan. It is running. I go downstairs and the inside unit is making a noise like the fan is barely running and almost hissing( quietly). Any ideas on what might be the problem? I have a new filter in and there is no leaks, or standing water anywhere.

any help is greatly appreciated.
Old 08-08-11, 11:27 AM
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Sounds like you may have a bad motor on the inside fan. If you turn the unit to either heat or fan only, the inside fan should come on and move air. If it is still "hissing" or "humming" then either motor is bad or if there is a start capicator, it may have went out. Look at fan and make sure nothing got sucked into the blades and is blocking it. Make sure you have power off when messing with the motor to ensure you don't get hurt!!
Old 08-08-11, 11:59 AM
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First, troubleshoot with a mutimeter - 24V to the contactor and 240V to the fan motor. If you don't have the experience, equipment, and skill to do this safely, best to call a serviceperson. Don't start throwing parts at it.

With the compressor running and the air handler not running, the hissing you hear may be the refrigerant vaporizing in the evaporator.
Old 08-12-11, 08:52 PM
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Look to where the copper A/C lines come out of the indoor unit, is the larger one frosted up? If so, the coil is likely a frozen block of frost/ice. You may need to set the thermostat to Fan- ON to de-ice,Do Not run the heat to do so. May be plugged condensate drain, water can't drain and instead gets blown onto an icy coil to freeze, particularly when humid after a rain.

Is the larger A/C copper pipe as warm as the smaller one? If so the compressor may not be starting due to bad capacitor, relay or other issue. Outdoor fan may run even if the compressor doesn't start. If copper pipes coming in/out of inside unit do not have a temperature difference (one warm or room temp and the other colder) see if you can hear the compressor running under the fan- would be a deeper hum if you can hear it. Carefully touch the pipes coming out of the outer unit, the small one could be Very Hot. If it is hot, then you require an HVAC tech. smaller pipe should be warm to the touch and larger pipe should be sweating water drops if it has been running for some time. Unless you are in the dry desert

If not sure if the compressor is running, turn off the breaker to the furnace for a few seconds and re-start, there is a time delay up to 5 minutes on some to prevent the compressor from coming back on to soon after stopping. Try to listen, you may be able to make out the compressor starting when the fan starts back up. If you hear it hum and then stop, the compressor may not be starting and then tripping off on overload. If after a few minutes it clicks and hums then stop again, it is tripping the internal overload.

If compressor seems to be running and larger pipe is cold, are you able to remove the front covers on the indoor blower section? Turn the power off first. If so there is likely a safety switch that has to be held in. This is to prevent the blower from coming on without the cover in place. DO NOT reach inside the area if you have power on whether holding the switch in or not.

If you are not sure which is the safety switch, Do Not touch anything else- If you get beyond your comfort zone, A/C no matter how hot it is is worth risking injury or worse.

If you turn the power back on and hold the safety switch button in, the control timer will eventually start the fan motor again. See if you can tell if it is running very slow, or just humming. If it seems like it is running strong but not sucking air past you, there may be a plugged condensate drain and water is freezing on the coil and blocking airflow. If the motor is running funny, and there look to be 10-14 wires going to the motor it may be a variable speed ECM motor with issues. If there are only 3- 5 wires running to it, it is likely a multiple speed or single speed motor, in this case it may simply be a capacitor issue or it may be a motor/control issue.

Not sure your level of experience here, but please DO NOT touch any electrical if you are not very experienced with such.

Re-post anything you find and someone will help...

Remember, Free advice is worth what you pay for it

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