A/C unit fan won't shut off

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Old 07-28-13, 04:49 PM
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A/C unit fan won't shut off

We noticed last week that the fan on our a/c wasn't turning off when the inside air had shut off. We have been unplugging the fuse and plugging it back in when we need to cool the house down, but this isn't a good long term solution.

We just bought a new contactor and installed that, however now the fan only turns on when we hit the button in the middle.

I've attached pictures of the old and new contactors. Where did we go wrong?
 
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Old 07-28-13, 05:43 PM
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You got to move one of the yellow wires to the top as in picture to one of the two prongs there.What you got is the yellows on the same place.
 
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Old 07-28-13, 06:02 PM
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A/C unit fan won't shut off

We tried that, but maybe we didn't have the right yellow in the top and bottom?
 
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Old 07-28-13, 06:10 PM
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Doesn't matter what yellow to top,maybe the transformer got shorted.Should check for 24 volts between the two yellows now.Or check at t'stat see if fan on turns fan on.
 
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Old 07-28-13, 06:12 PM
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no, because you wired it the way you did and tried to use the A/C you either blew the transformer or the fuse for the low voltage.... these components should be locate in your indoor unit.

On yellow to top and one to the bottom... it does not matter which one goes to which terminal.
 
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Old 07-28-13, 06:19 PM
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Hmm, ok so if we blew the fuse or the transformer on the inside unit, is it hard to fix? Sorry, I know this is basic but we have no idea where to go from here. Is the fuse easy to locate?

Thank you both for your help!
 
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Old 07-28-13, 06:24 PM
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I don't know anything about your exact unit inside (furnace or air handler) but it is typically a very easy fix once you find the fuse if there is one and or the transformer.
 
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Old 07-28-13, 06:27 PM
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Great! We'll look into that tomorrow and see what we can find out.
 
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Old 08-03-13, 09:49 AM
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So we re-wired the contactor so there is one yellow on top and one on the bottom. We also reset the main breaker and flipped the switches on the transformer, but the fan still won't turn on and the a/c isn't kicking in. I'm not sure where to go from here.
 
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Old 08-03-13, 10:06 AM
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You still need to check the fuse for the low voltage control in the air handler. It is probably either a 3 amp or 5 amp automotive type fuse and very easy to replace. Please reply with the make and model of your air handler and maybe someone here can help get you back in service.
 
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Old 08-03-13, 10:20 AM
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It's a comfortmaker but I can't locate a model #. I've attached a photo of what I think is the control panel for the air handler, is this helpful?
 
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Old 08-03-13, 10:42 AM
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The photo is pretty much out of focus. The model number should probably be on the access panel you removed to take the photo. Also, look for some documentation that shows the name and other pertinent info. To troubleshoot you will need a digital multi-meter. Do you have one? If so, and you are comfortable working around high voltages there are some basic tests you can perform to eliminate different items. To test the transformer you will need to set your digital multi-meter to VAC and place the leads on the transformer as shown in the photo. If the transformer is working properly you should have 240V (could be 115V on some systems) on the primary side and 24V on the low voltage side of the transformer. I would follow the blue and yellow leads from where they leave the transformer and test at the point where they are connected. I would follow the black and white leads from where they leave the transformer and test at the point where they are connected. If that test good then you need to look to see if you can see a 3 or 5 amp automotive type fuse on the control board. It may have blown when you connected the wires incorrectly on the contactor. Be careful working around live voltage!!! These procedures are just showing you how a test can be done. Since I don't have your specific make and model number I can't say for sure what your voltages should be. Some systems operate on 115 volts. If that is the case you would check for 115 volts on the black and white lead on the primary side of the transformer. Once we get the model number it will help narrow down what steps to take. I believe that the black plastic covering on the control board will snap off to give you access to the terminals and I believe you will find a fuse of some sort in there. It may be a glass fuse instead of an automotive blade type. If so, check the thin wire in the fuse to see if it is broken. I would shut the power off before removing the snap on cover.
 

Last edited by firedawgsatx; 08-03-13 at 11:48 AM.
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Old 08-03-13, 03:56 PM
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After doing some more research it looks like your unit operates on 115/120V. Here is an updated photo. The second photo is a control board that I believe is similar to yours. The fuse is the red rectangle with the number 5 on it in the upper right hand corner. Still can't say definitely until you provide model number and/or sharper photos. Some control boards have fuses and some don't even with the same part number.
 
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Old 08-06-13, 05:20 PM
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We purchased a multimeter today and tested the transformer and got no reading on either the high or low voltage side. I'm guessing we need a new transformer? We didn't look at the fuse since that was step two and we couldn't get past step one.

Does that sound like a correct diagnosis, or is there something else that we should try?
 
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Old 08-06-13, 06:10 PM
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If there is no input (120v)... then there can be no output (24v)... why is there no input? Door switch? Breaker tripped? High voltage fuse blown?
 
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Old 08-07-13, 07:47 AM
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Did you have the door interlock switch pushed in when you were testing the input/output voltage readings at the transformer? That switch must be pushed in or you will not have power at the transformer.
 
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Old 08-07-13, 07:54 AM
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Yes, we depressed the switch and also made sure the breaker wasn't tripped. Still nothing.
 
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Old 08-07-13, 08:41 AM
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Ok, then the next thing to do is to re-check the breaker again to make sure it has not tripped. Check your multimeter to see if it is working properly by testing one of your wall outlets to see if you are getting 120V. Then set your multimeter to VAC and see if you have 120V going into that furnace door switch. Do you have another breaker or disconnect box between the main breaker and your furnace? The photo shows a typical disconnect box. It might be a dedicated breaker. In newer construction you will usually find a disconnect located within 4' of the unit.
 
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Old 08-07-13, 08:52 AM
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The breaker was fine, but we will re-check the switch to make sure it is getting power when depressed. We don't have a breaker style disconnection box, ours is older and contains fuses. It was working just fine before and the fan will still come on if we push the button (although we don't want to cause damage so we haven't pressed it recently).
 
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Old 08-07-13, 09:04 AM
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So are the fuses good in the disconnection box? There has to be a reason why you are not getting power. Check the wire (probably black going into the door switch) to see if it has 120V. If you are getting power through the door switch then you will need to follow it through the control board. Were you able to get the model number of your unit? Right now a person trying to help you troubleshoot your problem has to guess how to proceed.
 
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Old 08-07-13, 09:12 AM
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The fuses on the disconnection box are fine. Maybe there is something with the wire from the switch. I'll check. I can't find any model # information anywhere. There's nothing on the panels that you remove to get to the transformer and anywhere it looks like there might have been information it is either gone or covered by Heating and Cooling company labels.
 
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Old 08-07-13, 09:19 AM
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Did you verify your multimeter was working properly? There is a small fuse in the multimeter. It's always a good practice to verify your meter is working properly before beginning troubleshooting. Without a model number it is difficult because to diagnose an issue properly a wiring schematic is needed. Can you get the part number off of the control board? It should be on the right lower quadrant of the board and start with ST9. Do you have a cutoff switch (looks like a regular light switch) that cuts off power to the unit for maintenance? Sometimes people forget to flip it back on.

If it was me, I would shut power off to the unit and remove the snap-on plastic cover on the control board to ascertain if there is a fuse on the board. If there is a fuse, I would then check the fuse to see if it is still good.
 

Last edited by firedawgsatx; 08-07-13 at 09:58 AM.
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