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Air conditioning panel and security panel are both showing blank

Both went blank.  The A/C unit for our home has its own circuit breaker panel.  I flipped that one off and on, plus all the other breakers on the regular circuit breaker panel.  They're both still blank.  My brother-in-law has an A/C friend who suggested using compressed CO2 to push out any blockages in the drain pipe.  

1) How do you do that?
2) Why does that even affect the display panel?

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Posted 2013-12-07T21:24:23+0000  by jugghayd jugghayd

We had an A/C man out and he mainly tightened some wires and got everything running again.  He also poured some bleach to clean up out the drain line, although that was not the source of the problem.


He said that the power supply to the security display was dead, but that it was completely unrelated to the problem with the A/C system and was just a coincidence.

He also let me know that I could have killed myself by touching the attic breaker.

Best Answer

Posted 2013-12-26T17:47:09+0000  by jugghayd

When you say the air conditioning "panel" what do you mean?  The thermostat?


By "drain pipe" I presume that he means the drain line for the evaporator condensate pan.  The "evaporator" is the part of the air conditioning system that cold refrigerant passes through to pull heat out of the air.  Much like a glass of ice water will have condensation on it, the evaporator pulls moisture out of the air.  That water collects in a pan under the evaporator and runs down a pipe out of the air handler.  Because there isn't a lot of water and it's relatively slow flowing the pipe can get "gunked up" (I know, that's a highly technical term).  Some HAVC tech will use carbon dioxide or nitrogen to blow the gunk out the line.  


I'm not really sure that a clogged condensate line would cause a blank display panel.

Posted 2013-12-08T02:07:23+0000  by Adam444

Yes, you're correct on both.  The thermostat is blank and the friend suggested it was a clogged drain line.

Here is the A/C unit in the attic:


And the PVC drain line:



There is another circuit breaker in the attic.  I tried flipping it off and on:


The outside unit.  The drain line is by the lower right corner if the unitIMG_4746.JPG


Close-up of the drain pipe:



And the exterior circuit breaker panel:

Posted 2013-12-09T19:50:07+0000  by jugghayd

A blank thermostat (did you check the batteries?) would indicate there's something amiss with the low voltage control circuit.  Assuming there is power to the unit, I would check for 24 VAC output at the transformer.

Posted 2013-12-10T17:45:52+0000  by Adam444

I didn't know thermostats had batteries.  I'll check.


"there's something amiss with the low voltage control circuit"
The what, now?


"I would check for 24 VAC output at the transformer"

Come again?



You'll have to talk to me like I have no idea what I'm doing (because I don't).

Posted 2013-12-10T17:48:16+0000  by jugghayd

Many of the programmable thermostats have batteries.  While they usually just are there to save the setting in case the power goes out, sometimes dead ones cause the thermostat to do weird things.


Most furnaces have a low voltage (24 VAC) control circuit that's powered by a transformer somewhere in or around the furnace.  The thermostat is powered by 24 volts and if that's out, it might explain the blank display.  The two most common causes are no line voltage getting to the unit or a failed transformer.


Posted 2013-12-10T17:59:25+0000  by Adam444
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