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Old 08-20-2009, 09:54 PM   #1
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Noisy solenoid chatter and compressor won't kick in now


Day and night AC/heat system about 15 yrs old. There is a bare copper tube coming out of the evaporator area that has a coil type 24V solenoid valve threaded into it. It appears to block gas flow out of the evaporator back to the condenser outside (educated guess). This solenoid usually makes one sharp click when the AC unit comes on. When I got home yesterday the solenoid was buzzing and chattering and the compressor won't engage, although the blower fan does come on. Could the coil be too weak to hold the valve open or is it more likely the valve itself is bad? There is some holding ability in the solenoid, it's not burnt out. Will the valve not opening make the compressor refuse to go? The AC was working fine.
Thanks for any tips!

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Old 08-20-2009, 10:06 PM   #2
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Noisy solenoid chatter and compressor won't kick in now


One of two things.

Either a weak transformer or solenoid is going bad.

If you can measure the solenoid in ohms and post measurement.

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Old 08-20-2009, 10:20 PM   #3
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Noisy solenoid chatter and compressor won't kick in now


OK I will
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Old 08-20-2009, 10:42 PM   #4
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Noisy solenoid chatter and compressor won't kick in now


If my cheapie multimeter is accurate the coil has 6.6 ohms resistance. There are three very small wires coming down to this area. The red wire has 11 volts dc whereas the white and green have no volts. One wire from the coil is attached to the white wire and the other to the red. When I connect the red wire the coil starts to chatter. If the solenoid is disconnected completely the compressor kicks in for a second or two before stopping. The thermostat seems to be detecting an abnormal condition and is cutting off the blower after a minute or two.
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Old 08-21-2009, 08:05 AM   #5
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Noisy solenoid chatter and compressor won't kick in now


Should be able to just change the magnetic coil. Before you do that make sure you don't have a voltage drop at the solenoid,

Should read 24v when activated, If the voltage drops significantly at the solenoid dis connect wire from solenoid and check voltage without the solenoid in circuit. If the voltage i lower than 24v, check wirig for pince and nicks.
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Old 08-21-2009, 05:21 PM   #6
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Noisy solenoid chatter and compressor won't kick in now


Doubtfull that you have a DC system. Most likely A/C. So your voltage readings are most likely incorrect.
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Old 08-21-2009, 06:05 PM   #7
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Noisy solenoid chatter and compressor won't kick in now


Quote:
Originally Posted by David H10 View Post
the solenoid was buzzing and chattering and the compressor won't engage, although the blower fan does come on.
There's a high resistance upstream which could be a bad neutral connection.
Measure the incoming 120 volt AC voltage on both sides of the neutral while the solenoid is buzzing.

Last edited by Yoyizit; 08-21-2009 at 06:23 PM. Reason: lack of clarity causing OP confusion in areas critical to understanding! Or not. . .
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Old 08-21-2009, 06:10 PM   #8
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Noisy solenoid chatter and compressor won't kick in now


Low voltage wiring has no nuetral.

If you read his post where he was checking voltage, he never checked for proper A/C voltage.

Could be just a bad solenoid.
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Old 08-21-2009, 07:35 PM   #9
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Noisy solenoid chatter and compressor won't kick in now


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Low voltage wiring has no nuetral.

If you read his post where he was checking voltage, he never checked for proper A/C voltage.

Could be just a bad solenoid.
Better watch out Been. He's liable to write an equation to prove you wrong!!!
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Old 08-21-2009, 07:41 PM   #10
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Noisy solenoid chatter and compressor won't kick in now


LOL.

1.4144 better be in the formula then.
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Old 08-21-2009, 07:46 PM   #11
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Noisy solenoid chatter and compressor won't kick in now


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LOL.

1.4144 better be in the formula then.
why is that number important?
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Old 08-21-2009, 07:53 PM   #12
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Noisy solenoid chatter and compressor won't kick in now


RMS.

Sine wave of 120 volts, peak is 169.728

120 X 1.4144 = 169.72

When reading with scope. 170 X .707 = 120.19
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Old 08-21-2009, 08:01 PM   #13
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Noisy solenoid chatter and compressor won't kick in now


I looked in my school notes from motor theory of 33 years ago.

It had all the equations you mentioned and more. My Final in motor theory was95%

Now i don't remember jack about the math. I guess it's true what they say, "Use it or lose it".
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Old 08-21-2009, 08:06 PM   #14
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Noisy solenoid chatter and compressor won't kick in now


Doesn't that 6.6 ohms sound a might off for a coil?
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Old 08-21-2009, 08:08 PM   #15
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Noisy solenoid chatter and compressor won't kick in now


"A high resistance upstream". Sounds like a job for Ex-lax

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