AC Not starting.. has power, no noise


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Old 06-01-13, 10:15 AM
S
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AC Not starting.. has power, no noise

Hey all,

So of course, on the hottest day of the season, the AC unit is not kicking in.

First I noticed that there was NO power at all to the AC unit. Check the plunger switch outside, it was on. Check the breakers inside and they were also on. After about 30 mins, I noticed the black hot was actually disconnected from the breaker on the panel. So connected that and rechecked the power at the AC unit.

240 v to the plunger switch thing
240 v to the one side of the relay
240 v to the other side of the relay

but still nothing... no noise, no hum, no fan, etc.

so... back inside, checked the thermostat. Set to cool and way below room temperature. Fan set to auto.

I can hear the circ fan kick in, the furnace kick, back outside and still nothing.

So... check voltage on the thermostat feed... and here's where I get a little confused and not sure what's suppose to be what...

I have a black and white wire... on the black, 24v, on the white nothing. At the relay, two yellow wires... one on the right side and one on the left... the right side which is fed by the black has 24v but the other fed by the white has nothing.

Soooo... I really don't know where the issue is and don't know how to troubleshoot much further at this point. Does anyone have any ideas. As far as I remember, this all worked fine last year.

Thanks!
S
 
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Old 06-01-13, 10:37 AM
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A lot of condensing units have a five minute (or so) delay before starting the compressor. This is to keep it from coming on under load. Sometimes when you check to see if it is running, it's just that the delay timer just hasn't timed out yet.

Doesn't answer the question about the black hot that was disconnected at the panel. Curious!
 
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Old 06-01-13, 10:46 AM
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Welcome to the forums.

If you are servicing like this and asking for help you should try to learn the names of what you are working on. Plunger thingy isn't very helpful.

240 v to the plunger switch thing
240 v to the one side of the relay
240 v to the other side of the relay
Is the plunger thing and the relay the same device ?

Name:  contactor.jpg
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This is a contactor. Do you have 240 VAC on both sides of it ?

The two red circled points are the 24 VAC to the coil.
 
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Old 06-01-13, 10:48 AM
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Explain where you are putting your leads to check voltage. The coil of the contactor should have 24VAC to pull in. The load and line side of the contactor should have 240VAC if it is pulled in.
 
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Old 06-01-13, 11:39 AM
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"Doesn't answer the question about the black hot that was disconnected at the panel. Curious!"

I really don't know... however, I noticed that the end of the wire was pinched. So i'm guessing that it was never properly inserted. It probably came loose when the electricians were in a few months back doing other work. We had a bunch of lights installed on the first floor.

"If you are servicing like this and asking for help you should try to learn the names of what you are working on. Plunger thingy isn't very helpful."

Lol... ok.. so the "Disconnect" has power and set to on and the "contactor" has power on both sides.

"Explain where you are putting your leads to check voltage. The coil of the contactor should have 24VAC to pull in. The load and line side of the contactor should have 240VAC if it is pulled in. "

The contactor has 240 on both sides in and out. Red on red, black on black? How do I properly test the 24VAC on the coil? And I'm a little confused as to how to test the 24 volt line that comes in. From what I've read, when its on, there should be no voltage?

I've also noticed a spring loaded mechanism on the contactor... its in right now.

I appreciate the help!
 
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Old 06-01-13, 12:11 PM
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Ahhhhhh...... so we now know the plunger thingy was a disconnect

Just foolin with ya.


In my previously posted pic I circled the two areas in red where the 24 VAC connects to the contactor. They are push on connectors. You should measure 24vac on them if unit is calling for AC.

From what you are telling us......you are measuring 240 VAC on both sides of the contactor and you say it looks like the contactor is pulled in right now. That would suggest that your unit should be running normally right now. Try removing one of the 24V wires. The contactor should open and you would lose the 240vac out.
 
 

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