AC control issue. Need help!

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Old 07-04-13, 07:01 AM
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AC control issue. Need help!

Wouldn't ya know it. Suddenly decides to go tropical and now the AC won't kick on.

I took the covers off the outside unit and with the system on and the blower running I have 120v between the small blue and yellow wires on either side of the solenoid.

If I manually push the contacts together on the solenoid, the compressor runs.

What I'm not sure about is whether I have a bad solenoid or something bad further up the line that is not sending the proper signal to the outside unit.

I changed the t-stat as it was acting funky, randomly clicking even when off.
the AC didn't work before the change either. The new t-stat instructions said not to connect the black wire labeled C. Seems strange but I left it disconnected.

Any thoughts or ideas what to check next?

*** EDIT Voltage on blue and yellow wires is 26.8, not 120v. Also Ohm reading between these 2 terminals with the system off is around 20 ohms + / - 1.5 ohms ( meter fluctuates )

Thanks
 

Last edited by CrispyB; 07-04-13 at 07:36 AM. Reason: Stated wrong voltage
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Old 07-04-13, 08:27 AM
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From the testing you've done, it would appear that the contactor (solenoid) is bad. One side should have 120VAC across the terminals, and the other side (blue/yellow wires) is connected to a 24VAC transformer via the thermostat. Since there is ~24VAC at the blue/yellow wires, that indicates that the contactor should be closed, thus sending power to the compressor & condenser fan. I would suggest buying a new contactor and try that. Be sure to turn off the power to the outside unit before doing any work on it.
 
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Old 07-04-13, 08:35 AM
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If you installed a thermostat that uses batteries then the C connection is usually not needed.

You checked and found 24 vac on the contactor and it is not closing.....is that correct ?
To check for continuity on a contactor coil you must turn the power off first. Remove the small wires from the contactor and then check it.
 
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Old 07-04-13, 08:37 AM
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From the testing you've done, it would appear that the contactor (solenoid) is bad.

Read more: http://www.doityourself.com/forum/ai...#ixzz2Y5j7IuT6
That's what I thought but wanted an expert opinion since I know little to nothing about how this all works.

I pushed the contact in manually and wedged a sliver of wood to hold it. So far everything is working good. I'll just have to operate it manually until I get a replacement.

Thanks Bob
 
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Old 07-04-13, 08:43 AM
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If you installed a thermostat that uses batteries then the C connection is usually not needed.

You checked and found 24 vac on the contactor and it is not closing.....is that correct ?
To check for continuity on a contactor coil you must turn the power off first. Remove the small wires from the contactor and then check it.

Read more: http://www.doityourself.com/forum/ai...#ixzz2Y5kNZxXc
Yes, 2 AAA batts in the new t-stat so thanks, that clears that mystery up.

Yep actually a tad over 24v at the contactor terminals with the t-stat on and calling for cooling.

I checked the ohms between the terminals for the small blue and yellow wires with the power off but the wires still connected and got ~20 ohms.

Unit is running now with the contact wedged closed so I may check with wires disconnected when the house cools down and I give it a break. Any idea what the ohm reading should be?

Part number of contactor is C147094P02

Thanks PJ
 
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Old 07-04-13, 09:16 AM
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There are safety switches in the outdoor unit that will interrupt the 24 volts to the contactor. So you need to be careful with how you are running your unit because if it develops a problem the compressor can be damaged.

The contactor coil could measure anywhere from 10-50 ohms as a guess.
 
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Old 07-04-13, 10:01 AM
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There are safety switches in the outdoor unit that will interrupt the 24 volts to the contactor.
Yeah I read about that in some other threads.I guess that would have to be the smaller diameter black wire at top left? The unit is 13 years old.

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Old 07-04-13, 10:05 AM
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The safety switches in your unit are low pressure and possibly high pressure. Those sensors are in series with one of the wires going to the coil..... not the power terminals.
 
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Old 07-05-13, 08:19 AM
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Checked a contactor coil for you,read 11 ohms.This was 2 pole 40 amp.Yours might be a few less,to lazy to dig out single 30.Please read without power and low volt.wires.
 
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Old 07-06-13, 05:15 AM
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Thanks for the info guyold. I will have to order the relay online as none of the local hvac contractors will sell parts over the counter, but they all would be happy to send a tech out

Before I swap it out I'll need someone to explain the proper way to safely discharge the capacitor though. It has 3 terminals in a triangle configuration on top iirc.

Thanks to everyone for their input.
 
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Old 07-06-13, 05:52 AM
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With a insulated screwdriver hit herm. and com. then fan and com. with the blade. That's at the same time 2 terminals.
 
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Old 07-06-13, 06:24 AM
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Don't forget to turn off the power to the compressor unit before discharging the capacitors.
 
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Old 07-06-13, 07:03 AM
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guyold

With a insulated screwdriver hit herm. and com. then fan and com. with the blade. That's at the same time 2 terminals
Bob14525

Don't forget to turn off the power to the compressor unit before discharging the capacitors.
Haha, yeah or this may be the result

Thanks guys
 
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