Need to replace heat sensor, where is it located on the unit?

The "OP sensor not connected" error message on a Honeywell HZ432 zoned 3-way AC unit indicates that there is a problem with the outdoor temperature sensor. The outdoor temperature sensor, also known as the outdoor sensor or the thermistor, is responsible for measuring the outdoor temperature and sending the data to the thermostat. If the sensor is not properly connected or is malfunctioning, the AC unit may not cool properly or may not function at all.
Here are a few steps you can take to troubleshoot and fix the problem:

1. Check the sensor connection: Make sure that the outdoor temperature sensor is securely connected to the thermostat. If the connection is loose, the sensor may not be able to send the correct data to the thermostat.
2. Check the sensor location: Make sure that the outdoor temperature sensor is located in a suitable place where it can accurately measure the outdoor temperature. It should be in a shaded area, away from direct sunlight and heat sources.
3. Check the sensor wiring: Make sure that the sensor wiring is not damaged or frayed. If the wiring is damaged, it will need to be replaced.
4. Replace the sensor: If the sensor is malfunctioning, it will need to be replaced.
5. Check the thermostat: Make sure that the thermostat is set to the correct mode and temperature.

Wouldn’t mount directly above heat pump due to graft from unit, outside anywhere is fine, directly behind unit likely best location.

Place your remote temperature sensor and the inside unit together for about an hour to see if they both read the same or if there is a large difference in the temperatures.

Dashes on the outside temperature reading may indicate that the inside unit is not receiving a signal from the remote. Change the batteries on the remote or change the location of the inside and/or outside units so that they can receive a strong signal between each other.

Your smartphone temperature may be coming from a location that is not near your home. They are often from a weather service. Where is your local temperature sensor located? Is it in the sun? Is it on the south side of the house, or another location where the sun or an air conditioner or other heat source may affect the accuracy of the reading? Try to locate your outside sensor in a shaded location with plenty of ventilation, and away from heat sources.

code p 0139 refers to heated oxygen sensor (HO2S) 2 bank 1--slow response===causes --heating inoperative--wiring--HO2S
or
oxygen sensor(O2) 2 bank 1---slow response===causes--wiring ---O2 sensor
as you have replaced the O2 sensor twice with no results then it will be the heated sensor that is faulty
heated sensors are the units in the exhaust manifold of exhaust pipe before the cat converter and O2 sensors are the units after the cat converter
It is normally the HO2 sensor that fails and the wiring problem is from not using the correct special socket for installation or removal that causes damage to the fragile wires to the unit

o2 sensor replacement will not necessarily clear code . It may be necessary to use a scanner for that . O2 sensors are located after the cat converter and is not a heated unit as is the HO2S unit

there are 4 o2 sensors on the nissan xterra . there is 2 o2 sensors in the exhaust pipe just after the exhaust manifold and there are 2 down under the truck

the o2 sensors are located in the exhaust system, theres one before the cat converter and one after,

your thermal fuse near the dryer vent opening or blower housing inside the unit,this is a one-shot fuse when it burns out you can't reset it,you need to replace it,then the radiant sensor(senses the flame),high-limit and cycling thermostats located on the burner tube on the dryer,then the boost and secondary gas valve coils located on the units gas valve body near the gas inlet to the burner tube

We would need more info as the model & make ..

however you could try replacing the heat sensor at the flip side of the machine..

Fame !

yes they could be defective check with multi meter and replace the one with no continuity sound from meter,no bleeping, make sure power is off