Here is a link to a Carrier outdoor temperature sensor. It may not be exactly your model, but the information could be helpful.

The sensor is a thermistor which a device which changes resistance as a function of temperature. There is a chart in the document showing temperature and resistance values. A 10K ohm reading would correspond to 77 degrees F.

Here is a link that might be useful: TSTATXXSEN01-B Outdoor Temperature Sensor

Mike:
I fount that page, thats why I thought it might be 10k, but I thiught it was for defrost function so maybe it should be for 32 degree.

The resistance of the sensor changes as the temperature goes up and down. The thermostat will translate the resistance value into a temperature reading. If the sensor has the correct resistance value at the current temperature, then it is likely to have the correct value at 32 degrees.

There may be another problem if the heat pump is not going into defrost mode at the correct temperature. Be aware the sensor will give a false reading if it is hit by direct sunlight.

MIke:
I just checked the one on the system and its around 5k, so I put a 10k resistor on it and the error went away. So I just ordered a new 10k thermistor from digikey.
Thank you
Larry

Thermistors can fail such that the resistance curve does not change correctly with temp variations. It may read correct at a particular temperature and incorrect at higher and/or lower temps.

Well I replaced the old one with a 10k. At first the E3 went away, but as the outside temp started down I got the E3 back again. Its not cold enough for defrost only 56 outside now.
So now I do not know what the problem is. If I push the Up/Dn at the same time I get - - and od. Which means its not working. If I open the thermostat and check S1 and S2 going outside i read the thermistor value, about 10k when I put it in,now its 2.2k So no open wires. I cant check the voltage on the thermistor without soldering wires on S1 and S2 to bring them out to test. Or removing it from the wall and stripping the S1 and S2 wire because when the thermostat is closed its behind the front and open there is no connection. So either 10k is the wrong value or there is something else wrong.

I am not sure I follow how you are testing the temperature sensor. Does this thermostat display the outside temperature and if it does is it correct?

Have you tried measuring the resistance of the sensor at various temperatures and see if it flows the temperature chart. Put the sensor in the refrigerator or freezer and see if it tracks. Do this with the old sensor also.

You can't measure the resistance of the sensor when it is connected to the thermostat. If the thermostat is powered any current in the circuit may produce incorrect resistance readings. If it is not powered then anything in connected in parallel with the sensor will change the resistance value.

You may have a resistive short between the the S1 and S2 wire connections. This resistance would lower the resistance readings of the sensor and cause errors in some temperature ranges. If you really want to test the wires and sensor you going to have to isolate them from the thermostat.

Check to see if the thermostat is getting 24 volts between the R and common connection. Check the voltages across the S1 and S2 and see if you get the DC values listed in the document.

This is sounds like a thermostat problem but do as much checking as you can before investing in a new one.

You have to open the thermostat cover which disconnects the pins that the thermistor is connected to, so those pins just go to the wires that the thermistor is connected to nothing else S1 and S2. Like I said It read 10k at 75 and 2.2k at 59. I forgot to look at the chart to see if it was tracking correct. Its brand new.
Again I can't check the voltage because I can't get to S1 and S2 with the thermostat open unless I go outside and strip the wires, which I was going to do today, but I just read the resistance again and its down to around 850 ohms. So something is weird. I still have to check the voltage. But the resistive readings now is way off and the wrong way off. I will check it outside in an hour or so.

I removed the thermistor and it now reads 200 ohms, its bad. I checked the voltage and its about 5v. I guess I bought a bad thermistor. When I put it in it was 10k.