question about outdoor temp. sensor


Old 04-04-03, 02:27 AM
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Join Date: Mar 2003
Posts: 150
question about outdoor temp. sensor

I've had a carrier h/p, electric furnace system with a Thermidistat. It has been great for the 1.5 years that I've had it.
The problem now is that the outdoor temp sensor will not go below 75 degrees F. It seems stuck on that temp. If I put my hand on it and run inside and check the temp, it will rise, but it will not drop below the 75 degree mark.
Could the sensor be defective.
I have the sensor located under a porch, well protected from sun, rain, and I have the wires from the sensor spliced to the wires coming from the house.
Any help, advice would be greatly appreciated. Thanks
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Old 04-04-03, 11:14 AM
hvac4u's Avatar
Join Date: Aug 2001
Location: NW atlanta
Posts: 3,147
that sensor

runs off of resistance, could be a wire, wire connection or the sensor itself. can you ohm it out? will have to be very sensitive meter.
Old 04-05-03, 04:40 AM
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hvac4u hit the nail on the head.
What you have is commonly referred to as a thermistor.

To properly check it you should have a chart that shows the resistance in ohms at a particular temperature.
Barring that, if you remove it and connect an ohmmeter, the resistance should change with the temp, as was suggested.
Old 04-05-03, 06:17 AM
Join Date: Nov 2002
Location: Massachusetts
Posts: 1,816

We know that it changes with temp, but does it properly reflect the outdoor temp? You'll need a thermometer to measure the outdoor temp, a thermistor chart, and an ohm meter.
Old 04-05-03, 06:23 AM
Join Date: Nov 2002
Location: Massachusetts
Posts: 1,816
Wink OH!....

Some of these remote sensors are polarity sensitive so reconnect in reverse order. Check this reading from the thermostat with the wires disconnected. Don't condem the thermistor if it fails there, till you check it by its nearest connectors to the thermistor itself ( Probly just inside the wall or in a 2X4 handy box).

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