A/C is working sporadically

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Old 09-09-19, 07:19 AM
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A/C is working sporadically

Hey everyone, My A/C unit has been acting really weird lately and it started about 3 months ago. It works and then stops working. I have done different things which will cause it to strat working again so bear with me on the long post :-).
When I have the thermostat set to cool, the outside fan and compressor will not come on, but the blower on the furnace will so it will be blowing hot air. We had a technician come out to look at it, but of course the unit was working when he came out. He checked both the furnace and the outside unit and said there was no shorts and everything looked okay with proper voltage going everywhere and nothing clogging the drains.
Of course it went out and assuming that maybe it is just over heated, I would shut the system down from the switch at the furnace and start it up at around 8pm and it would work throughout the night. The next day, it would shut down again. I decided to change the thermostat, capacitor and the contactor outside, even though the voltage was showing correctly when tested. This did not help. I called the technician out again and now it was not working. He saw the yellow wire that was connected to the a/c circuit board on the furnace was not completely under the screw. He adjusted it and the outside unit started back up and worked fine for a month. The outside unit recently started acting up again so I would go upstairs and unscrew the yellow wire and re screw it in and the A/C unit works fine. I am tire of having to do this every time the outside unit will not come on and I always check to make sure the wires are completely under the screw each time. Does this sound like the A/C circuit board might be bad?
 
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Old 09-09-19, 07:51 AM
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What outdoor unit do you have? Is there a circuit board in the condenser?
 
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Old 09-09-19, 09:20 AM
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Hi, when it happens again, try removing the yellow wire from Y1 at the Tstat and see if you get the same results, post a pic of the control board.
Geo
 
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Old 09-09-19, 12:01 PM
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I do not know exactly what brand it is but I will find out when I get home. No, there is not a circuit board at the condenser. I will try removing that Y1 at the Tstat tonight to see if I get the same result. Here is the pic of the control board in the attic.
This is my first time trying to upload something on here so I think it is there. :-)
 
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Old 09-09-19, 12:13 PM
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Removing the Y1 wire will cause the air conditioner not to run at all.
Is there a condensate overflow somewhere?
 
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Old 09-09-19, 12:27 PM
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There is, it is below this to the right but the cut off switch to that is in the normal position and there is no condensation/water in the overflow pan. The condensation is dripping outside.
 
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Old 09-09-19, 02:53 PM
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Hi,roughneck77 I was not thinking of leaving it off , just removing it the same way he was removing it from the board, to see if it produced the same thing as removing it from the board, could be another issue.
Geo
 
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Old 09-09-19, 04:15 PM
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The outside unit is a Lennox Elite. It has not gone off yet so I have not had to try it from the Tstat.
 
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Old 09-10-19, 05:02 PM
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Okay, so the AC stopped working again this afternoon so my wife went up and shut off the power to the blower. When I came home, I disconnected the Y on the Tstat and put it back in. I then flipped the power back on to the blower and the AC fan and condensor came on so I think it worked this way as the same wad unhooking the y on the furnace circuit breaker.
 
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Old 09-10-19, 06:34 PM
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If you are being tortured and it sounds like it, and you spend time on the board, I think it is a wise choice to change it. You do not know what it looks like on the other side. It could be there is something going on that is causing intermittent function. I have seen this before. I swapped out boards and that was that.
 
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Old 09-11-19, 11:28 AM
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You may want to use a meter to check to see if you have 24V at the yellow wire on the board when this problem occurs, if not, check the yellow wire at the T-stat, If you do have 24V at the T-stat, then board or wire issue, if not , T-stat issue. If you do have 24V at the yellow wire on the board, then check the contactor terminal and find out why the contactor is not working. Hope this will get to the bottom of the problem.
 
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Old 09-11-19, 12:09 PM
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Hi, when this happens you do have 24 VAC at the contactor coil? I believe thatís what you said in a earlier post.
Geo
 
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Old 09-11-19, 03:00 PM
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When it started up, I tested the original contactor, it was showing 240v coming in, 24v at the coil. I replaced it anyways just to make sure there wasn't something "phantomly" wrong with it. After the replacement, it was showing them same readings with the meter, 24v across the coil.
I am going to check the board once it goes out again.
 
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Old 09-11-19, 03:58 PM
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Right after hitting reply, my ac went out. I checked the voltage at the Tstat with the red and yellow and it read 26 but when I went to the circuit board at the furnance, the red and yellow did not read anything. The red and c read 26v as well as the red and fan wire.
 
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Old 09-11-19, 04:10 PM
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0V between R and Y means your unit was calling for cooling.
24V between R and Y means your unit was NOT calling for cooling.
0V between C and Y means your unit was calling for cooling.
R and Y are the same circuit when cooling is running.
 
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Old 09-11-19, 04:28 PM
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Thanks, but the weird thing is, the yellow wire is screwed tight on the circuit board when it stops running but starts back up when I loosen the screw and retighten it.
 
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Old 09-11-19, 04:32 PM
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There should be 2 separate conductors on the Y terminal. One coming from the thermostat. The other running to the condenser.
The board in the furnace as a whole has no bearing on turning the condenser on and off, besides providing 24V to the R terminal. The thermostat handles on and off functions of the condenser.
 
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Old 09-11-19, 06:21 PM
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Yes, there is a wire also going from the y terminal to the condensor. I am going to try to crimp the 2 wires since they might be vibrating and loosen the connection to the y terminal, maybe this will fix it.
 
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Old 09-11-19, 06:26 PM
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One wire on each side of the screw head. Tighten down till neither wire can be pulled out by hand.
If there’s that much vibration going on you have other problems.
 
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Old 09-12-19, 03:40 AM
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@roughneck77 that sounds better so I am trying that. I was over thinking this. I do not think there is a lot if vibration because I watched it turn off, turn on and run. Maybe since the 2 wires were twisted together to connect to the y terminal, the screw could not evenly clamp down?
 
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Old 09-12-19, 06:22 AM
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Hi, that terminal on the control board is probably just a junction point, I would try taking the 2 conductors off and just wire nutting them together
Geo
 
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Old 09-13-19, 03:16 AM
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Well these did not work either. I did just realize something this working while looking at it. This morning when it was not working, I took the voltage meter to check the R and Y terminal, when I connected meter to both terminals, I heard a click and everything started outside. I assume this means their is a short on the circuit board?
 
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Old 09-13-19, 04:47 AM
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Like I said before, the board isn’t responsible for turning on the condenser. That said, it could be a broken solder connection on the R terminal behind the board. Next time it happens check for 24V at the thermostat.
 
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Old 09-15-19, 05:26 PM
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Thanks again for everyones help. The ac was working this weekend up until right now. While the blower was running but the outside unit stopped, I checked the voltage at the Tstat. Their was voltage. I went to the circuit board and checked r to c with 0v and then c to y with 0v. I went to double check r to c and when I used the voltage meter, the fan seemed to "restart" and then the voltage showed 26v from c to r. When I checked c to y again, I heard a click and then it was showing 26v and outside unit started.
 
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Old 09-25-19, 02:23 PM
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It has been cooler here so the ac does not been running as much but the last 2 days, it has been hot again and starting cutting out again. When it is out, I am not getting any voltage between c and y or c and r but noticed that if I tap the power relay, it will close and start everything up and I get voltage. Does this mean the board needs to be replaced or is the power relaying opening for another reason? I was planning on replacing the board but wanted to make sure there was something else that would cause this.
 
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