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Old 05-28-2009, 12:29 PM  
capntaco
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Default Wierd problem related to outdoor temperature

Hello,

I have a condensing unit that is about 15 years old connected to a 35 year old air handling unit. The unit is for A/C only, since I have electric heat. The air handling unit is a Singer brand and I don't remember what brand the condensing unit is. The air handling unit is in the attic. The system is controlled by an old-fashioned dial thermostat, not an electronic one. I typically keep the house at 60 F at night and don't run the A/C during the day.

The problem is that when the outside air temperature is below about 60 F, the air handling unit stops but the condensing unit keeps running. It will do this all night if I let it, regardless of the interior temperature. It doesn't matter what I set the dial to on the thermostat, the air handler never starts back up again unless it rests for several hours or the air warms up outside. This never happens if the air temperature is greater than 60 F. (The 60 F figure is empirical; two nights ago it was about 63 F for a low and it ran fine, then last night it was 55 F for a low and it quit.) I have a few questions:

1. Is this bad for the condensing unit?

2. Is this a problem in the condensing unit or the air handler?

3. Does the air handler control the condensing unit?

4. Would either of the devices have an automatic shutoff that stops the device from working at a certain outdoor temperature?

Thanks,

Will



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Old 05-28-2009, 03:31 PM  
kok328
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1. Is this bad for the condensing unit?
Yes, you stand the chance of freezing up the evaporator coils like a block of ice.

2. Is this a problem in the condensing unit or the air handler?
Don't know, will have to troubleshoot to find the problem. Possibly a stuck contactor on the compressor.

3. Does the air handler control the condensing unit?
No

4. Would either of the devices have an automatic shutoff that stops the device from working at a certain outdoor temperature?
It is possible (but not likely) that there is a low ambient tempature sensor that will cut out the compressor, not the air handler.

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