AC not cooling but everything seems to be in order

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Old 07-27-16, 11:51 AM
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AC not cooling but everything seems to be in order

So I have this problem that I haven't been able to figure out. Any help would really be appreciated.

I noticed that our downstairs AC (Lennox) had stopped cooling all of a sudden. The temperature wasn't going any lower so I read through the forum and checked the condensate pipe. The pipe was indeed blocked and the overflow drain had water in it. I used a vacuum cleaner to clean it out and started the AC again. No water this time in either of the pipes. The outside fan comes on and the motor inside the cover comes on for a few seconds and then shuts off. I can hear a low humming from the AC in the attic and the ouside fan is still running but there is no air in the vents and no cooling. Is the inside motor shutting off within seconds of starting causing it? Why would the motor shut off? What can I do to fix it. Please help.
 
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Old 07-27-16, 12:58 PM
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Can you switch the inside fan to ON at the thermostat?the motor inside the cover I assume is inside the condenser outside, correct?
 
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Old 07-27-16, 01:14 PM
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I changed the fan setting from auto to On in the thermostat. The motor inside the cover is like right there as soon as I take the cover off. There is 1 long cover on the unit and the small motor is right behind it.
 
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Old 07-27-16, 01:43 PM
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Is this outside or in the attic?
 
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Old 07-27-16, 02:03 PM
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The outside fan is working fine. I checked the capacitor and it seems good too on the outside unit. It''s the inside unit where it comes on for a few seconds and then shuts off.
 
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Old 07-27-16, 02:11 PM
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Do you know what type of blower motor your air handler (inside unit) uses: PSC motor or ECM motor? If it's a PSC motor, there will be a capacitor located somewhere near the motor. If it's an ECM motor there is no capacitor used, however ECM motors are notorious for failing after 5 years or so of use. Usually, it's the control module on the back of the motor that goes bad.

If the blower motor isn't running, the system will freeze up, so don't run the A/C until you get the blower running again.
 
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Old 07-27-16, 02:24 PM
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How do I check the motor type? The motor on the front comes on for a few seconds, then shuts off. There is a control panel in the back with 2 LEDs that blink green to signify normal operation.
 
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Old 07-27-16, 02:34 PM
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If you post the complete make & model number of your air handler, we may be able to look it up for you. Otherwise, you would need to pull the blower assembly out and look for a capacitor. If you find one, it's a PSC motor. If you can't find a capacitor, it's likely an ECM motor.
 
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Old 07-27-16, 03:15 PM
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I went up and took some pictures. I couldnt find the capacitor but the motor you see up front does come on when I switch the AC off then on for a few seconds then I hear a few clicks in the back panel(pic also attached) then everything shuts off.
 
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Old 07-27-16, 04:14 PM
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The motor you show in your picture is NOT the blower motor. It is the combustion air motor and is used as part of the gas furnace. It should only be used for heating, not for cooling. I did find the installation manual for your gas furnace. Your furnace uses a PSC motor. The capacitor is mounted on the outside of the squirrel cage assembly. Below is a link to the manual for your furnace showing where the blower motor is located.

http://www.google.com/url?sa=t&rct=j...TEzRjEOgC8k01g
 
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Old 07-27-16, 04:23 PM
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Thanks Bob, do I have to remove the blower from the unit in order to get to the capacitor? Is the diagram on page 13, Figure 11 the one you are referring to? Given the symptoms do you think it is that capacitor and if so, what is the easiest way to get to it to replace it?
 
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Old 07-27-16, 04:32 PM
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Yes, figure 11 shows where the blower motor capacitor is located. Often when a motor won't start, the capacitor is the culprit. The capacitor is relatively inexpensive (should be <$20), so it's usually the first thing to be changed. The capacitor can be checked, however you need a multimeter that has a capacitance mode (not too common). It's usually cheaper to just replace it rather than buy a special meter to test it.

You probably won't have to completely remove the blower assembly (Fig. 11), however you likely will have to slide it towards the back of the furnace to get to the capacitor and wiring. If you have a voltmeter, you could check to see that you have AC voltage going to the blower motor before replacing the capacitor. If you don't have any voltage, the motor won't run. It depends upon how much diagnostic work you want to do rather than just replacing parts.
 
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Old 07-27-16, 06:16 PM
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I would snap a few pictures before removing the blower access door.
Wires can pop off of the control board sometimes and it is easier if you have some pictures. Be sure to turn off power first.

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Lennox had another model that made access to the blower difficult.
It was the 80MGF...

 
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Old 07-27-16, 07:49 PM
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Thanks both you guys, I was able to read through the manual and open the access door. I didnt take any wires out, I just switched it off from the switch by the AC unit. I also only moved the door only enough to allow me to get to the capacitor. I'll take it into the local Lennox store in the morning to test the capacitor and replace if needed. I'm thinking of also taking the outside dual capacitor as well, in case it's that one that is bad. What do you guys think?
 
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Old 07-27-16, 08:23 PM
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No, not the outside one. the outside capacitor has nothing to do with your inside blower.
 
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Old 07-28-16, 05:06 PM
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Ok so I changed the capacitor on the blower but nothing changed. Everything still keeps humming when I turn the power on. Anything else I can check or is it time to call in the pros?
 
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Old 07-29-16, 03:52 AM
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You've done all you can without doing some diagnostic work, which requires a multimeter at the minimum. Is the humming coming from the blower motor or somewhere else? Did you try spinning the squirrel cage/motor to see if it turns easily (power off)? If the motor is humming and spins easily with the power off, the motor itself may be bad. If the motor isn't humming, then it's possible that it's not getting power. To measure voltage at the motor, you'd need a multimeter.
 
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