Blower unit hums faintly when off

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  #1  
Old 12-20-16, 05:23 PM
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Blower unit hums faintly when off

My blower unit is in the attic.

During the Summer, the central A/C unit worked perfectly. Now, I switch to Heat in Auto mode, it will not turn on. But if switch to ON, the blower unit kicks in but no heat, temperature intake=outtake.

At the thermostat (Hunter), if I turn it OFF, the blower unit faintly hums. When I go back in the attic, what should I look for?

Thanks.

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Old 12-21-16, 05:52 AM
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That's an electric furnace so when the stat is set to auto the heat and blower are started by the sequencer. If you have a meter test between W and common to see if the stat is sending 24vac.

BTW, the installer should be slapped for running the cables and high voltage wires right in front of the access door.
 

Last edited by skaggsje; 12-21-16 at 05:56 AM. Reason: added
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Old 12-23-16, 02:57 PM
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I've measured RC to W/B and RC to Y/O (photo), and both shows 29.5VAC. When measured G to RC, it shows 29VAC. Everything else shows .5VAC or less (G-W/O, G-W/B <.5VAC).

Also, I tried the COOL and it still works (condenser and blower kicks on). But when switched to Heat, and increase the temperature setting, I can hear the click sound on the thermostat, but no blower.

So the thermostat seems to be working ok. And since A/C (Cool) kicks on, it can't be relay or fuse on the blower unit, right? I'm bit confused.

According to the thermostat manual, G is the fan and W/B is the heat. If I short G-RC and RC-W/B, is the heat supposed to kick in if the unit in the attic is ok?

I agree, the cabling is horrible. The workmanship isn't what it used to be. Even my current A/C guy, I have to call him every time season changes on my two houses.

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Old 12-23-16, 03:14 PM
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if I turn it OFF, the blower unit faintly hums
The hum you are hearing is likely nothing but the control transformer and is nothing to worry about. It converts 120 volts to 24 volts for the stat.
 
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Old 12-23-16, 03:29 PM
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I din't think about that transformer constantly converting... Good to know. What else should I check next for no heat/blower? Thanks.
 
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Old 12-23-16, 05:10 PM
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Have you tried new batteries in the stat?

If this is an electric furnace, are the breakers on for the heat strips?
 
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Old 12-24-16, 07:49 AM
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When I removed the thermostat, the LCD stayed on while I was testing, so I'm guessing the batteries are good. But I'll test the battery when I get there this morning.

Are you talking about that 2 breaker switches on the front of the blower unit? Yes, they were both on when I was testing, although the photo shows off.

I'll check the limit switch today.

Also, according to the manual, RH is also 24V, but it's not connected. Does it need to be jumper to RC? According to the manual RC and RH should be jumpered if there is no RH wire. And the brown wire wasn't hooked up, I'm guessing it's a spare.


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Last edited by itchibahn; 12-24-16 at 08:39 AM.
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Old 12-24-16, 10:33 AM
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Resolved....

I put a jumper between the RC and RH, and all working like it should.

I don't understand why the jumper was missing to start with. I had my AC guy check it out when I bought this house earlier this year. I'm wondering, because I had to call him twice a year when season changes on all both of my houses....

Thanks for all your help. I just saved $125 trip charge.
 
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Old 12-24-16, 10:43 AM
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Talk about psychic..... I saw your wiring on the stat and was just typing my reply.

Good find.
 
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Old 12-25-16, 06:13 AM
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According to your picture of the breakers, they are in the off position. They should be on for electric heat strips. Perhaps there is a heat pump?

I'm wondering, because I had to call him twice a year when season changes on all both of my house
He would just move the red wire from RH to RC, or vice versa, depending on the season. That sounds like a scam to get you to call for service.
 
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