No more a/c on Auto thermostat setting


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Old 07-07-19, 09:56 AM
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No more a/c on Auto thermostat setting

I have an older a/c system (lightly used through the years) with air handler in attic and compressor unit outside. I have a RobertShaw thermostat that controls the a/c. I usually set it to AUTO and just dial the temp down to kick it on for a few hours during the day (an attic fan is used at night when hot).

The other day the unit (air handler fan and outside compressor unit) would not come on in the AUTO setting. When I dial the temp down below the indoor temp, I hear the thermostat click but the air handler fan does not come on (usually the outside compressor unit comes on minutes later). If I put the thermostat in the ON position, the air handler fan does work but the outside compressor unit does not come on (which i assume is correct for the latter). I have reset the thermo.

I checked voltage to the leads in the thermo and they are 24+.

I thought it may be a bad thermo...or something (relay?) in the air handler?

(I do have another Honeywell thermo that governs the baseboard hot water oil heat but never added the a/c wires to it).

Thoughts?
 
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Old 07-07-19, 05:09 PM
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Although unlikely, it is possible that the thermostat is bad. If you take a jumper wire and temporarily connect terminals R to Y on the thermostat, the outside unit should come on. If it does while jumpered, but not when the thermostat calls for cooling, then the thermostat is bad. If you jumper R to G, the blower should turn on. If you jumper R to G to Y, you should have A/C (both outside unit and blower running).
 
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Old 07-07-19, 05:41 PM
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With the air handler in the attic you MAY have a condensate overflow switch in the drain pan or the drain piping from the air handler. IF you have this switch AND the drain line has become plugged it may have allowed the condensate level to rise enough to stop the compressor or entire system.

You need to inspect the drain line for it being open and free to drain the condensate.
 
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Old 07-16-19, 06:48 AM
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I jumped the R and Y and the air handler fan goes on (attic). When I jump the R and G the same thing happens.
The outside compressor does not come on at all.

Just odd that it stopped working in AUTO (no air handler), In ON mode the air handler comes on but not a/c unit (but assume that is correct).
 
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Old 07-16-19, 07:00 AM
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I see a small pipe from the air handler box that would drain into the pan below the entire thing. It seems fine. The pan is bone dry too.
 
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Old 07-16-19, 02:53 PM
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Got a guy in.... seems the thermostat was bad.. And now the relay in the compressor was bad. Maybe due to mice pee after i removed all the nest (though it had worked a few days). Hoping new relay tomorrow fixes it.
 
 

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