The year of the AC issues...

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  #1  
Old 11-02-20, 05:55 PM
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The year of the AC issues...

So here are my last 2 issues (both also on downstairs unit).

https://www.doityourself.com/forum/a...d-working.html
https://www.doityourself.com/forum/a...run-cap-2.html

This time I'm getting nothing from the thermostat controls. No fan blowing, no calling for AC or heat. I removed and checked it and seems OK. Wires look OK. Batteries seem OK. I cycled power on the furnace/blower in the attic...

Any other low hanging fruit to try first? This thing is 15 years old. Feels like I'm on borrowed time...

Thanks.

 
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Old 11-02-20, 06:22 PM
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Did you re-read the second thread ? This is basically the same problem you had then.

Check for 24vAC from C to R.
Make sure to hold the blower switch in.

 
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Old 11-02-20, 06:29 PM
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Last 2 times the blower was working. I just checked it with fan switch on and and it wasn't turning. I spun it by hand and it started turning very slowly.
 
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Old 11-02-20, 08:08 PM
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It sounds like the blower motor has gone bad. It could just be a capacitor but typically the motor bearings go bad and cause that slow starting..... almost like a growling.
 
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Old 11-03-20, 05:14 AM
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There is no humming or any noise at all if I hold the door switch and hand spin the blower wheel with the fan on at the thermostat. Could it still be the capacitor? If so, I'll remove it and check it.
 
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Old 11-03-20, 06:47 PM
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I would definitely check it first.
 
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Old 11-03-20, 07:40 PM
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Thanks, haven't tested it yet but went ahead and bought an $8 replacement.
 
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Old 11-05-20, 10:02 AM
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After discharging, I set the multi-meter to 200M ohms and the reading slowly climbed to ~196 and went back to 1. However, if I do this test set on 200K nothing moves.

So it seems the cap is good? Please confirm.
 
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Old 11-05-20, 10:34 AM
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To correctly test a capacitor you need a meter with a capacitor section.
Your test shows the cap has some capabilities but there is no way to tell how much or if it's in parameters.
 
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Old 11-05-20, 11:01 AM
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OK, I'll replace with the new one when it arrives and go from there.
 
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Old 11-07-20, 12:00 PM
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So its not the cap. Any tests I can do to troubleshoot the motor without replacement parts?
 
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Old 11-09-20, 07:19 AM
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Perhaps another way to approach this is to figure out if its the motor or a larger power issue. There are no breakers tripped but I toggled the one to the furnace anyway. But when I toggle the power switches at the furnaces, the problem one makes no sound but the working one makes a click sound in the unit. Any suggestions how to verify there's not a bigger electrical issue?
 
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Old 11-09-20, 10:39 AM
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You had said you gave the blower a push and it started turning slowly.
That usually means it has power. You could check and verify for AC power to the motor.
You've eliminated the capacitor. That doesn't leave much else.
 
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Old 11-09-20, 04:35 PM
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I checked my working furnace and the red light on the control board lights when the door switch is closed so now I'm leaning toward a faulty board.

I then checked for 120v b/w the door switch line terminal on the board to common on the transformer (OK), then 120v between black and white terminals on transformer (OK), then checked the right side between red and blue for 24v (FAILED), then checked for 24v between where those wires go in to the white plug (FAILED), then checked voltage between R and C (FAILED).

So can I now assume that the board is toast?
 
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Old 11-11-20, 01:48 PM
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Could it be the transformer since it seems no power coming out of it? I also assume no red light on board when door switch is pressed is a big red flag?
 
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Old 11-17-20, 02:19 PM
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It was the transformer...but maybe not the only issue. I now have power everywhere but if I call for cool, the outside condenser does not turn on but the fan does. If I push the plunger/contactor at the condenser the unit does run. If I call for heat I hear the furnace turn on but the fan doesn't come on. If I bypass the thermostat I get the same results so I don't think its that. So I guess there could still be a board issue but I don't know how to confirm that.
 
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Old 11-17-20, 02:46 PM
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Spoke too soon. Now back to previous state so new transformer "blew". Could bad board be doing that? No other power issues I'm aware of.
 
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Old 11-17-20, 08:07 PM
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It maybe time to bring someone in. You're going from one problem to another.

I checked my working furnace and the red light on the control board lights when the door switch is closed so now I'm leaning toward a faulty board.
Your red light was working. Then it wasn't working. Are you shorting things out ?
Transformer went bad. Now another one went bad. If that is true something is shorting it out.
It's rarely the board. It could be a thermostat wiring short.

This whole problem started with just a motor issue. Things seem to have gotten worse.


 
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Old 11-18-20, 01:18 AM
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At 15 years that cap might be bad. Worst case scenario you replace it and it doesn't fix it. With the fan wiggling after you spin it that makes me think that's the problem though. I'd start there. Remember that caps can keep juice even when you cut the power so be careful if you swap it.

Or pay a guy 65 bucks to come out and check it for you. They can diagnose it and tell you what it'll cost to fix, then you can fix it yourself or if it's not too expensive just let the guy do his job.
 
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Old 11-18-20, 04:36 AM
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It wasn't a motor issue. There was just no power to anything. The blower fan worked fine while the power was temporarily restored.

@BaldBull I did replace the cap first thing. Not a bad idea to pay a diag fee and go from there but I'll give a go a bit longer since weather is cooperating (mild in NC).
 
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Old 11-18-20, 07:32 AM
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Don't wait too long. It may take up to 2 weeks to get parts in. Ask me how I know that one, haha.
 
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Old 11-27-20, 07:59 AM
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So, turns out I had connected the common wire from the control board to "b" on the thermostat after I replaced the Nest earlier in the year. Guess I never called for heat until now.
 
 

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